52v, 32ah single battery, skateboard config (box under cargo floor)
KT and Bafang displays
160 Nm rear, 45Nm front
SIDEBAR:
This is bike had a fairly involved build with lots of neat details. However thats not what this article is about. Build details will be discussed in a near-future article dedicated to the subject.
My previous AWD builds all used effectively the same front wheel setup: A 35a controller mated to a Bafang geared fat motor packing an 80 Nm punch. It was so powerful, on my early commuter bikes I needed to turn down acceleration via a slow-start setting. When I graduated to a combination mid drive+hub, I found best results on rough trails came from the same slow start, but also using the front power sparingly: little if any throttle and gentle PAS.
There things stayed for a few years – roughly from the middle of 2017 to early 2021. During this period I concentrated on riding and refining the use and configuration of these AWD bikes. I built other bikes during this time- all more traditional single-motor mid drives. As part of that work I came up with tuning settings that worked very well with pedaling and a cycling mindset. These changes worked great with the 2Fat AWD bike as well.
With regard to tuning, I concentrated on backing off the BBSHD’s power when delivered in ‘pedelec’ mode: limited use of throttle and pedal assist only. The point of this was to have a bike that did not run away from me, still delivered measurable, useful levels of assist, lacked the common complaints against cadence-type assist and did not suffer from any of the weaknesses of torque-sensing.
When 2021 arrived and I wanted to build a bucket-list bike – the Larry vs. Harry Bullitt cargo bike – I decided to go all out and make it AWD. Further, I wanted to prove a concept I had been mulling over for the last few years. For lack of a better term, lets call it Drama-Free AWD: what a normal person who just wanted a reliable automobile replacement would want to ride.
Ingredients
Its a pretty short list:
Low power High power in a front wheel can be fun, but its not necessary to gain the traction benefits that come with AWD. Use a smaller, lighter, relatively low-powered motor (45 Nm vs. the prior 80 Nm) as part of its design. Also use a smaller controller that peaks at 25 amps rather than the previous 35. Continue to use the slow-start setting to ensure … Drama Free AWD. 25 amps on a smaller diameter wheel will still be a strong assist, but those amps will be rolled on slowly so no surprises.
Fast Wind Front Motor The Bullitt has a 20″ front wheel. A ‘fast wind’ motor favors torque off the starting line at the expense of higher top speed. This is normal for a small wheel build and further solidifies the emphasis on slow, strong startup power that melts away on its own as speed increases.
Toned-Down Rear Motor My revised motor settings keep the BBSHD from engaging until speed goes past 5 mph if I rely on pedal assist. I learned how important that is to drivetrain longevity when I built 2Fat. We’ll re-use those identical settings.
What I Expected
On a bike destined to carry heavy loads, the front motor is intended to get the bike off to a painless start. It does this job very nicely. Despite the relatively low power, it still gets the bike rolling from a stop, and effectively takes out the BBSHD’s shock to the drivetrain when that second motor kicks in at 6 mph.
That reduced sting will translate into reduced wear and tear, and reduced parts replacement over time. Its too early to pull hubs apart and look inside to verify this assumption, but since I have seen and verified the effect before on similar hardware, there’s no reason to assume different results.
It was a short list of things to expect and… it all panned out. But there were also some pleasant surprises. This turned out better than I thought it would.
What Surprised Me
I noted above the motor is ‘fast wind’; built for low-speed torque, not high speed rpms, and how this plays into the smaller front wheel size. Intellectually, thats easy to understand. Less obvious was the fact that, in practice, there will be a lot less motor usage than there was before.
With The Great Pumpkin, I usually run both motors at equal levels (usually full blast) all the time. The bike and flat, straight streets just lend themselves to a high speed cruise. Two identical motors and identical controllers gulping juice from one battery mean a big power drain. No surprise.
With 2Fat, while I reduce power to the front motor, I was often giving the bike hard use on trails. More often than not the bike is fighting its way up a hill, thru a bunch of sand etc.
So even though The Lizzard King is not dramatically different than 2Fat in terms of its configuration, the world it lives in is quite different: level and smooth city streets. Easy acceleration and long periods of the motors spinning fast while running at an efficient cruising speed.
More different still: Off the line, the front motor kicks in slowly and then power melts away as wheel revolutions increase. It pulls strong from zero to about 15 mph. But from 16+, it starts dialing back as the motor approaches its rpm limit. By the time 20 mph rolls around, on typical level 2 assist you are down to about 200 watts of output. By the time you hit 24 mph on flat ground, wattage to the front wheel has minimized to a steady… 37 watts. Just enough of a dribble to ease the wheel’s free spin.
If you hit an incline, you’ll slow down a tad and see wattage output creep right back again. But rolling down the street on the flats, the front motor takes itself out of the picture and its time for…
… The rear motor to kick in. As noted, pedal assist does not engage the rear motor until it touches 6 mph+. So when the front motor is eating the most juice, the rear motor hasn’t even started up yet. As the mid kicks in and spools itself up, the hub begins making its graceful exit.
The two motors never really run hard together at the same time unless you are climbing a hill. Then you can see the watts climb up on the front rather than fading away. Once you level off to a cruise at a fairly high cadence and speed of 24+ mph , you are on the single rear motor being given a small boost from the front motor (remember those 37 watts?).
All this translates to an overall reduction in expected battery drain, consisting of both reduced peak and continuous draws. It gets better though.
Much Better!
The rear BBSHD is also using a lot less power than its siblings in The Pacific Fleet.
At 20 mph, on PAS 2 in the front and maybe PAS 4 or 5 in the back, looking at both displays, I can see 250-300w being output from the rear motor, and another 150-200w being output from the front. 500w or less are being drawn between the two motors, on a great big cargo bike. All the way up and down the speed curve, watt and amp output for the BBSHD is much less than it is on any of my other bikes.
Not So Fast!
All of this wonderfulness is only true when running under pedal assist. If I decide to, I can mash the rear throttle and the BBSHD will, as usual, peg the gauge until I release. And that means it will burn thru my battery range lickety split. Not a surprise. there is no free lunch in this world, but if we stay off the throttle we can still get a hefty discount.
And I still configured my big single battery (custom-built for this bike) to the usual theoretical limits: A 25a peak front controller and a 30a peak rear controller mean I must have a battery management system with a bare minimum of a 55a continuous rating, and preferably 60 (mine is 70). I would rather not take any chances, but clearly I have a bigger safety margin than I figured on originally.
Commercial Manufacturing
Should a commercial bike be made with this Drama Free AWD kind of approach in mind, a thoughtfully designed system could manage power in such a way as to map out the curves on the individual motors and develop something that never bumps into the limits of a much more conventional BMS. That makes for a battery system less expensive and easier to source in volume. And a street machine is going to have lower power needs than is generally understood to be the case with an AWD bike.
Lower power means safety for the casual rider, lower cost and smaller battery sizes.
Lower power on a street bike could look like – in the USA at least – dual motors fitted to bikes that still remain legal within both federal manufacturing standards and individual state vehicle codes. A 249w front motor and a 500w rear for example. Or even a 250/350.
Whats the Takeaway?
The fact that I can operate a great big bike like The Lizzard King at power levels well below allowed USA ebike power limits is testimony to the fact that viable, useful AWD can operate well within the legal framework of ebikes in this country.
Just because you have two motors does not mean they both have to be running simultaneously at full blast. Turns out… not doing that can be kind of a big deal.
Built to conquer the weakness of twin hubs in hills – and eliminate the damage a mid drive does to an ebike’s drivetrain. The bike I call 2Fat did all that.
So, my Gen 1, 1.5 and 3 bike layouts are all twin geared hub designs. What was Gen 2?
2Fat
750w, 35a geared Bafang G060 front hub motor
30a BBSHD mid drive
52v, 12.5ah rear motor battery in triangle
52v, 12.5ah front motor battery on rack top
Batteries connected in parallel to form a single ‘virtual’ 25ah power source to both motors
KT and Bafang displays
160Nm rear… 80 Nm front (do the math on that one!)
I live part-time in two towns: The first, an extended work visa, is in Fresno California, smack in the middle of California’s San Joaquin Valley and flat as a table. I built The Colonel, The Purple Thing and The Great Pumpkin for commuting in Fresno.
While I most often take pics of it in a wooded area, 2Fat is just as happy on paved, hilly roads. Shown here with front panniers, its 4-bag carry capacity makes it a quasi-cargo bike.
After a fashion, I finally was able to get a big enough bike rack on the back of my SUV to bring the Colonel to my actual home in Pacific Grove, California. My house is at the top of the hill there. Unlike in Fresno, nothing in or around the area is flat. You are either going up a steep hill, or down one, or both.
My intention was to be able to use the Colonel like I did in Fresno, as local errand transport and a light duty cargo-shopper. Unfortunately, I found out the first day about the limitations of hub drives: They suck in hills.
Hubs are Single Speed
Hub drives power an ebike via the axle. They don’t – and they can’t – use the gears of the bike. Forcing a single speed hub motor up a hill makes it just as miserable as a human stuck with no gears. So even though I have very powerful hubs, and they were geared hubs that put down the most torque of any on the market… they still struggled. Even with two of them. I could hear the gears groaning inside the motor casings and I could tell that, while I could get up the hills, my motors were not happy about it. I did not want to lug them into an early grave. I had already gone to a lot of trouble to make the bike bulletproof and had no desire to ignore the problem and inevitably kill it.
These twin 80Nm hub motor wheels were on The Colonel at the time of my first hill country ride (above). Now they are on the Great Pumpkin.
The solution?
I Need To Build a New Bike
Everybody knows mid drives are the solution to the hill problem for an ebike. A hub motor is single speed and at least relatively weak on torque, but a mid drive uses the gears in the drivetrain, plus it has double or more the torque output of a hub, and thats before you factor in the multiplier of the gears. Wonderful right? Except mid drive motors – especially DIY builds – are notorious for putting drivetrains into an early grave. Why? Well because they pour a LOT more power through the chainring, chain, rear cluster and cassette body (i.e. “the drivetrain”) than a bicycle was ever meant to withstand.
A normal cyclist can pump out maybe 300 watts for a minute or so, but typically normal sustained – strong – output is about 100 watts.
EU-market electric motors must peak at 250w of output to stay legal (pssst… they don’t).
A 25-amp BBS02 on a 48v system puts out in excess of 1250 watts peak
Your garden variety 30-amp BBSHD running under a 52v battery is peaking – and can sustain – about 1750 watts of output.
My rear rack trunk battery. The capped red wire is for charging. The black wire on the rack stay is power output to the front motor. This is the original dual-separate-battery config
That gives some perspective on how much abuse is heaped upon a drivetrain with a mid drive. Coming off the successful builds of The Colonel (v1.0) and the Purple Thing (v1.5), I knew AWD reduced load on the individual motors dramatically when they work together as a team.
Given that, I thought about how I could use a front hub to reduce or eliminate the shock that a mid-drive puts onto the ebike’s drivetrain. Not only would I gain the traction benefits of AWD, and the benefit of reduced load from the team effort – things I already knew were a big positive – the front hub would also, if used in a slightly different way, provide an important added benefit: eliminating all the extra wear and tear that goes with having a mid drive.
If it worked, it would give me a bike with all the original AWD performance benefits, plus the ability to effortlessly climb walls, without tearing the bike up.
SPOILER ALERT: It worked unbelievably well.
New steel on the right, used alloy (1000 miles of use) on the left. And this was WITH AWD to reduce the wear and tear. Ordinary single-motor systems with this mileage would be dramatically worse. Substituting the steel body eliminates all wear.
In fact this bike is a showcase on how AWD can almost eliminate mid-drive wear and tear. Making a bike that climbs hills and bombs trails really well is almost an afterthought.
So that is what I am going to focus on here in this article. What was built and how was it used?
The Build
Briefly, this bike is the Great Pumpkin on the front wheel, and a typical mid-drive installation on the back. In between is the usual extra wiring scattered all over the place to deal with powering two motors, set up dual PAS etc..
The Front Motor
2Fat has another Bafang G060 80Nm front fat motor installed – this time its inside of a custom-built 100mm double-wall Weinmann (branded as an Origin8) rim. Go fat or go home. Attached are the same two torque arms as seen on the Pumpkin’s installation, and once again the controller is sitting in a grommeted handlebar bag that doubles as a wallet/keys/phone holder. It also serves to disguise the uncut steering tube I used to give me a more upright – but not too upright – riding position.
Another big, fat, 80Nm front hub motor. This time laced into a 100mm rim. Because fat bike.
Different from the Pumpkin is the battery setup. This bike was built before the v3.0 Pumpkin came onto this Earth (The Purple Thing had just been born). So, lacking the wherewithal to commission a big custom battery for the triangle, I used two packs, one for each motor. The front motor’s 12ah 52v battery was located in the rack trunk at the back of the bike. I had already learned I did not want to put a battery on the front rack as it made the steering too heavy. The rear motor’s 17.5ah pack was in the triangle.
It could be worse: Tucked in between the panniers in the rack trunk is one of two batteries. The second pack is in the triangle. Whats on the front rack? A weatherproof, adjustable 5a charger.
Additionally, due to the very low standover of 2Fat’s Large sized frame thanks to its top tube (it is a titanium, USA-made Chumba Ursa Major) there is not enough room to plug in a properly big battery in the triangle to handle both motors. So I had to do two batteries and live with the awful choice of putting one on the back rack.
After running the two dissimilar, separate batteries from its initial build in 2017 to March 2021, I switched to two identical, now-parallel’d-together packs in the same locations. Each is 12.5ah (14S6P) with Samsung 25R cells. Each has a 50a continuous BMS. As such, the system has a single 25ah power supply with a BMS capable of handling 100 continuous amps. Considering I can never peak past 65, I’m in great shape. I purchased the packs from Bicycle Motorworks, who builds their packs in the USA and constructs them at time of order.
Sidebar:
Running battery packs in parallel should only be done by those who have done the research and know exactly what they are getting into. In this case, both packs are identical, being manufactured to-order together, and have the same charge cycle count. Their voltages were matched before they were joined and there is some additional babysitting that will be necessary for charging and balancing. If you can avoid running packs in parallel and use just one battery: Do that instead.
Using two entirely separate batteries is a kludge and your last resort. Not only will you have to charge them separately, you will also draw down the two batteries separately at different rates which will result in uneven remaining power, lesser range and more frequent recharges.
The Rear Motor
This is pretty much your garden-variety 52v BBSHD installation. It has a couple of nice spiffs in the form of a 42T Lekkie Bling Ring, and Lekkie Buzz Bars, but neither of those things are a requirement of the AWD approach we’re discussing here.
The rear wheel is another matching Weinmann 100mm rim, again with DT Champion 2.0 spokes and 16mm brass nipples. The rear hub is a DT 350 Big Ride, which has sealed cartridge bearings and has been upgraded to a steel cassette body. Additionally a 9-speed Shimano HG400 cluster gives me steel cogs literally welded together into a single cluster, that spreads the enormous torque of the BBSHD across the entire steel cassette body. The DT350’s ratchet engagement mechanism is one of the few known bombproof rear hub mechanisms when faced with the power of the Dark Side 30a BBSHD motor.
A solid rear wheel build with extra strength parts throughout is crucial to a successful mid drive ebike.
205mm front and rear rotors with Magura MT5e brakes
The Special Bits
There is a bit more that went into making these motors work together. The complete integration possible on the Pumpkin thanks to the use of identical motors and controllers wouldn’t work here.
Brake Cutoffs
Trying to share cutoff signals between the motors again – using adapters for the red-to-yellow connections found on the BBSHD – resulted in bricking both motors. I tried everything to share the signals. It can’t be done unless you are willing to install a second, independent set of hydraulic magnet style cutoffs, zip tied to the integrated MT5e cutoffs and connected via a ‘y’ further down the line. That would work but it would look like crap, for very little benefit over what I ended up doing: I set up the front brake to engage the front motor cutoff, and the rear – with a red-to-yellow HIGO adapter – to cut off the rear motor. Since I always use both levers to do my braking I get an effective result.
Pedal Assist
PAS for the BBSHD is built into its motor casing, so it just works. PAS for the front motor was another matter entirely. Ordinarily the assist disc and sensor runs on the right-hand, drive side of the bike and hides behind the front chainring. This is not possible with the BBSHD’s secondary gear housing being there instead. So PAS had to be made to work on the left hand side. The KT controller has left-hand PAS sensor installation settings.
What was needed then was a left-hand install. This was quite a bit trickier, since the 120mm motor running in front of 5″ tire-compatible chainstays had zero extra spindle length to mount the disk. Lacking a bottom bracket cup to mount the PAS sensor ring, I set it behind a second inner lockring – I used two inner lock rings stacked like jam nuts rather than the usual inner+outer ring. These doubled inner rings had the secondary benefit of being a more aggressive, solid mounting for the motor.
With the sensor mounted, next I had the sensor ring to deal with. As noted above… there was no length available period for the sensor disk as the crankarms mounted pretty much flush to the bottom bracket.
The eventual solution involved hogging out the center of the PAS sensor disc so it could sit on the inner flange of the Lekkie crankarm instead of the spindle. I prepped the crankarm with… thin strips of thick duct tape so the disk would sit tightly on the flange. It was a bodge but it worked, and with just one improvement since installation in 2017 it has held perfectly. That improvement is a zip tie to help hold the disk steady in position (of course I used a zip tie. We have duct tape in the mix; all thats missing is a zip tie).
Worth noting: I used this identical PAS ring mounting when I built the Lizzard King AWD cargo bike in 2021. Not only did I have enough extra spindle so I did not have to do this surgery on the ring, I also realized I could unscrew and reverse the sensor in its mounting ring. This eliminated the need to use the reverse settings in the display/controller. Since the inset ring was reversed, it was outset now… and that held the sensor closer to the magnets (they work fine inset as seen here, but closer is better).
The Cockpit
Here’s where the eagle-eyed may spot a preview of how I ride this bike to soften up the mid drive.
Those are Jones SG bars with ESI XL Extra Chunky grips, wrapped in silicone tape
On the right, we have the grip, then the brake lever, followed by the 9-speed shifter. Here again we see a v2.0 feature that v3.0 fixed: A SRAM drivetrain gives us a SRAM, not Shimano shifter. The Shimano shifter needs so much real estate on the grip it is impossible to put a throttle on that side of the handlebars. Look at the cockpit of The Great Pumpkin and the Lizzard King to see how a SRAM shifter solves this and lets me do one throttle per thumb.
Being unable to do that at the time – and believe me I tried EVERY possible combination of throttles. I still have most of them in a box in my garage. I settled on two styles of thumb throttle, side by side on the left, with the innermost throttle being for the hub/front and the outermost for the BBSHD/rear. As for the eagle-eyed part: The front throttle is cocked higher so between that and its longer throw, it is engaged first and when at 100% it follows the natural curve of my thumb. Both throttles can then be at 100% and my hand stays comfortable at WFO.
How To Ride It
At last we get to the point!
I already let the cat out of the bag earlier: The biggest deal associated with this bike is not that it can climb really well (REALLY well). Nor is its ability to handle trails and rotten conditions its star quality.
2Fat was made to get dirty
No, the real point of having a mid drive teamed with a front hub motor is to use that hub motor to take the shock off the drivetrain that mid drives deliver. Do that and you also take away the excess wear and tear on the parts (if we are being fair, a lot of this comes from doofus riders who don’t know what they are doing).
When starting, start with the hub
This is most of the deal right here. Don’t make the mid drive haul the bike up from a dead stop. Its got the torque to do it. But everything takes a beating in the process. The nylon gears inside of the mid drive. The chainring. The poor chain. The suffering cogs. The cassette body being dug into by the cogs. The pawls inside of the cassette body that are straining against the hub. Your ebike hates you for doing this to it.
By using a mid-drive-strong chain, a steel cluster and a steel cassette body with a ratchet engagement mechanism, we harden the drivetrain to be very tolerant of this abuse. Between that and learning how to use a mid drive, wear and tear really isn’t bad at all. Maybe no worse than a quality analog bike used hard. But still… even with the hardened drivetrain it sure would be nice to take things easier.
By using a hub motor to get the bike rolling – even by just a few mph – we accomplish this mission. Using my pedaling-friendly BBSHD programming or something like it, the BBSHD will not kick in on pedaling until the bike crosses about 5 mph. So from a stop, you hit the front throttle for about one full second. That throttle is cocked up a bit higher on 2Fat to make that a natural move. The bike starts up from its dead stop without any strain on the drivetrain since the BBSHD is not even running. Simultaneously, you also start pedaling. This engages the cassette mechanism.
When speed crosses 5 mph, the BBSHD’s pedal assist now kicks in on a drivetrain that is already engaged. There is no longer a risk of having the motor jerk the chain and smash the cluster into engagement. And with this gentle engagement, the motor starts working on a bike that is already moving. So you get the doubled benefit of a lighter effort against all components to get your fat bike off its fat ass. Instead, you get smooth – and strong – acceleration. The lack of lugging the motor has the further benefit of not generating anywhere near as much heat since the motor is no longer running at low rpms for anywhere near as long. And those nylon gears inside the motor are writing you a nice thank-you card.
Or…
Rather than using the throttle, you could also just start pedaling. I have set the KT controller to engage PAS as quickly as possible. Combine that with the BBSHD’s controller being told to hang back for the initial startup, and you have a completely thumbs-off solution that implements at a nice gentle pace.
So… It just works.
Or you can force it! Remember with this setup you have two throttles. There’s no law that says if you need it, you can’t jump the gun and either hit the rear throttle early, or hit it so the motor engages harder than it would have in your designated PAS mode. So if you need a little extra push thanks to an XL load of groceries, or a steep hill, you have options at your disposal.
Downshift? Schmownshift!
One of the mantras associated with smart mid drive riding is that you always Always ALWAYS freaking downshift the bike when you come to a stop. The LAST thing you want is to lug the motor up from a dead stop because of all the brutality it visits on your chain, your cogs blah blah blah. So that means you remember to downshift one or two… maybe even three times before you come to a stop. When the light turns green you upshift in sequence one gear at a time as you get back up to speed again. Thus as we all understand: you row thru the gears.
Another rule mid drive mavens repeat ad nauseum is – if you have an 11T small rear cog… stay the hell off of it. Its too small to use on a mid drive. It bogs the bejesus out of the motor from a stop, its too small to be able to get up to speed before the sun sets and if thats not bad enough, the teeny cog on even the steel Shimano clusters is alloy and it is not attached like all the others are. Its an individual. So not only do they dig into the cassette body harder, they die fast. Like Really Fast. As in a few hundred miles tops.
Well, on AWD mid drives like 2Fat, you can forget about all that. Because of the powered front hub doing its part (either thru a quick dab of throttle or just letting PAS start the bike), there is no longer a need to shift at a light. You can forget about the whole process. Just leave it and it’ll be fine as if it was a hub motor! In fact the front motor allows the bike to increase its speed so it gets up and goes fast just like a hub motor does.
I found this out within a day of building the bike, and since then learned from experience the 11T cog will last about 1500 miles before it typically cracks (two so far). Thats not so bad for a readily available US$7 part. And if I wanted it to live longer, well it wouldn’t kill me to go up a gear at a light once in a while.
At the office, outside my e-garage. There is a trail network along my commute route that 2Fat lets me take
Wrapping It All Up
2Fat itself is not the ideal example of how to execute this concept. It is a product of when it was built and my knowledge level at that time. In the present day, I for sure would not want to build a bike with two batteries, and if I did I would NEVER put one on the back rack. But thats partly the limits of the frame I used. I came within a hair of using a Salsa Blackborow frame kit for this bike until, at the last minute, this titanium beauty fell into my lap for a song… but thats another story.
Next, I wouldn’t use Shimano components thanks to the real estate problems introduced by the shifter. Instead I’d use SRAM components so I could do one throttle per thumb.
Really the Great Pumpkin with its XL size and XL triangle, plus its SRAM shifters – would be ideal here. But them’s the breaks. This is what I’ve got. Boo hoo.
With that said… I did learn as I went along, and in 2021 I returned to dual motor bikes with the Lizzard King, a bike meant to prove a different kind of AWD could be awesome: You don’t need the 80Nm, 35a punch of the Pumpkin’s or 2Fat’s front hub to gain the benefits of AWD. A low power implementation, done a little differently, should be very effective and appeal to a much broader range of everyday, low-speed, low-drama ebike use. And…
This is a common question on BBSHD and BBS02 motors, so I thought I would write up a quick post and describe what can be done, and what I do.
Here’s The Problem
If you shift under power with a BBS02 or BBSHD, you will do so using a LOT more power than your ebike’s drivetrain (chainring, cogs and chain) was ever designed to handle. Shifting while under even a moderate amount of power is a great way to snap your chain and take the Walk Of Shame home. Worse: you can crack or even taco a cog.
Here’s The Solution
Use a gear sensor. Thats not so tough, right? First of all, what is a gear sensor? Its a little box, with a little wheel inside. You run your shift cable thru the little box, in one side and out the other (which means you need to cut and re-section your shift cable housing), with the cable running across the little wheel. When the wheel senses any motion, it sends a signal to your motor that cuts the power for a split second and takes the pain away from your drivetrain when a shift occurs.
Whats Wrong With That?
Nothing, so long as it works. The little wheel inside is mechanical and crud-sensitive. Lots of folks have issues with them not working after rain storms or mud baths. You can solve that by wrapping it somehow to keep the grit out.
I wrapped this sensor in silicone tape to make it crudproof
Its also not the ONLY way to do the job. Like I said, I had my first BBSHD without one. I learned to shift without needing a gear sensor. By the time I built my second bike, I had that method down pat. So yeah sure the sensor is nice but I have already learned another way, and I have found – even though I have bought sensors and have had them right in front of me during a new build – I don’t feel a need for them.
But I sure as hell have a need for the job they do. Everyone does. So don’t let anyone tell you the problem is not real. Its probably the #1 way to snap a chain on a mid drive bike.
Gear Sensor Alternatives
So there are a number of different ways to do this job. I’ll list the one I use last
Use the brake cutoff as a clutch
Its simple: Squeeze the brake handle just a little bit to engage the brake cutoff. That cuts power to the motor and gets you the same thing a gear sensor does. The trick is to not engage the brakes to any noticeable degree and lose any of that hard-won momentum. Interestingly, Magura MT5e ebike brake levers have a special little hinge in the middle of the lever. It lets you do this more easily without engaging the actual brakes.
See that little metal pin in the middle of the lever? That hinge makes this lever a shift cutoff. Touch it with a fingertip, the brake cutoff engages, the motor cuts out and the pads aren’t touched.
Thats nice, assuming everything works. If you are a little jumpy, or the bike is bouncing along a trail or something, then that delicate caress on the brake lever might be a little more than you figured and … well, you get it. We live in an imperfect world. But this method still works pretty good.
Use a cutoff button on the handlebars
This is definitely not a common solution, but it does work, and is what I used on BBSHD Bike #1 until I gave up on it and perfected the method I describe next.
See the green button at the center of the pic? Thats the cutoff switch
What is it? Its just a dead-man switch on the bars. Press it and for as long as you hold it, the motor is cut off. Release it and the motor re-engages. Its a brake cutoff that has no brake pads. The other end of the switch has a yellow Higo/Julet that connects directly to the BBSHD’s motor cutoff plug.
In practice, I found it took too much thinking to reach for the button just prior to a shift. It felt forced and I didn’t take to it. Maybe you will and if so its a dirt cheap and simple method to try that doesn’t involve screwing around with your shift cables.
Adapt your pedal cadence
This is the method I settled on, and even after buying and successfully using a gear sensor, I have never felt a need to install another one. This method is just a natural part of my riding style now and is trained into muscle memory… so I do it naturally and automatically on any bike no matter what. Here’s what I do, in order. These steps occur in very rapid succession so making a shift happen occurs in about one to 1 1/2 seconds.
Step 1: Stop pedaling.
Step 2: Click the shift (just one gear).
Step 3: Start pedaling. Muscle power completes the shift before the motor kicks in
Thats it. Do it fast and its just a quick stutter in your cadence. Changing your BBSxx settings so they are friendly to pedaling helps. The linked settings will cut the motor off fast and start it back up soft. Perfect for completing a shift.
When you get good at this, you will be able to click your shift a hair before the motor stops the rotation of the chainring. My more recent builds use SRAM 11 speed drivetrains that need only about 1/4 of a cog revolution to complete a shift. So if I do it right, I click while there is still a ghost of rotation left that makes the shift, so when I start pedaling again I’m already working with a shifted gearset.
But…
Don’t try and get fancy right out of the gate. Just keep it simple and get the shift done. The high speed fancy stuff will come naturally as you gain experience.
Remember, there is nothing wrong with a gear sensor. They do their job. I just learned how to do without one. Having done that, I don’t feel a need to make the effort to install the sensors anymore.
In an ideal world, you do both. Truth be told I screw up every now and then. With the cadence technique and the sensor backing it up, you are pretty much guaranteed to never snap a chain thanks to shifting like a fathead.
A big bruiser geared specifically to be pedaled hard at 32-34 mph, this is my commuter workout-workhorse. Don’t want to sweat? Just relax and pedal easy… at 28 mph.
1 x 52v, 30ah battery with Samsung 30Q cells, 90a continuous BMS
2 x 35a KT brand controllers
2 x KT brand displays
160 Nm total power
The Great Pumpkin remains my fast commuter workhorse. This bike is meant for transportation to and from a destination, not sightseeing. As such it is designed to travel as close to the safe, legal speed limit as possible. Here in California the assist limit is 28 mph, I stay on the street (no shared-use bike paths allowed) and this bike’s gears are made to let me power it up past that 28 mph limit to about 34 mph – if I am strong enough to pull it off.
A note on speeds and our local roads here, and how they influence the design and capabilities of this ebike: in California the law limits ebikes to 28 mph (45 km/h) of assist. Thats an assist limit, not a speed limit. The maximum lawful speed is the posted motor vehicle speed limit, adjusted downward if necessary to maintain safety. So if you can pedal the bike faster than 28, thats fine so long as doing that is "safe for conditions". These speeds seem like a lot to readers in some parts of the world. But remember here in the USA we've got open roads that are nothing like you see in many urban centers in, for example, the EU. The two pictures above come from two different places along my 15-mile commute route. The speed limit signs are in mph not km/h. Bear in mind drivers regularly exceed these limits by a significant margin so in rush hour traffic a 30 mph bike is by far the slowest thing on the tarmac, with no pedestrian issues to speak of.So, on streets like this, if I can pedal to 34 mph - and oftentimes I can - thats perfectly legal. In fact I have been paced and radar'd by police cruisers and motorcycle traffic enforcement many times without incident.
So the secondary purpose of this bike is to enable me to work hard while still transporting me to Point B at a practical speed. You’ve heard how ebikes let you arrive at your destination without getting all sweaty? Well, this one lets you arrive all sweaty on purpose if you like.
The geared hub motors let it accelerate fast in traffic, and despite its necessary lack of suspension, the fat tires (and the suspension seatpost) let it ride well on lousy pavement. It has over 7000 miles on it at present (March 2021), and benefits from all of the learning I got the hard way building its predecessors. In fact, I am using the same set of wheels I had built for my very first AWD ebike: The Colonel. This is a testament to finding a good wheelbuilder at the Local Bike Shop of your choice and have them build you a quality wheel with quality components.
Fresh from the wheel builder in March of 2017. DT Champion 2.0 spokes, 16mm brass nipples, double-wall Weinmann 80mm rims. Still going strong today, three bike builds later.
Motor Choice
The Pumpkin is a flat-country bike. Dual geared hubs are powerful, but hub motors – since they power thru the axle and cannot use gears – are just single-speed. Despite their power and ability to handle lots of current, they can get the bike up steep hillside streets, but they struggle doing it. Riding this bike in the Carmel/Pacific Grove portion of the Monterey Bay Area, where nothing is flat, I found it could climb anything but it lugged its motors mightily doing so, to the point I feared for their long life. But if you live on flat land (and this bike’s permanent home is in the table-flat San Joaquin Valley), this is the design that will gobble up pavement for lunch. It will get you where you need to be safely and quickly as an ebike can legally travel.
Why didn’t I choose maintenance-free direct drive hubs? Because they lack torque, and that means slow acceleration unless I load the bike down with bigger, higher voltage batteries and motors with much more unsprung mass.
Battery
Having done it the wrong way before out of necessity (translation: too expensive) I put in a single big battery on this bike. It has the biggest battery I could fit into the triangle of this XL-sized frame (A Chumba Ursa Major made with chromoly tubing). A 14S9p (52v) pack that uses Samsung 30Q cells to give me about 30ah. That means it takes awhile to charge. But it also takes awhile to drain, and this single battery is placed down in the triangle where it does not reduce the carry capacity of the bike, or screw up its performance with schlocky placement of a battery on the rear rack.
But doing an AWD bike with a single battery means you have to address more than just size. The Battery Management System (BMS) has to be able to handle the amp draw of two motors simultaneously. Looking for batteries out in the wild that can do this… you’ll find almost none that are capable of it.
Initial battery fitment prior to connecting the power and charging cables. The bag hides a multitude of cable-routing sins.
How do you calculate the sort of battery you need? You take the peak output of both of your motors and add them together. Your BMS’ “continuous” power rating has to be more than that peak to ensure your motors never trip the BMS’ limits. If they do, to reset the battery you have to hook it up to a charger, which is unlikely to be handy on the side of any road you’re traveling on.
So, with a 35a rear controller and a 35a front controller, I need a battery with a 70a continuous (or more) BMS, and thats a special order item. In my case, the BMS can handle 80a continuous current.
Controllers and Wiring
The 35 amp KT brand rear motor controller is sitting under the saddle, zip-tied neatly with small clear, low-visibility ties to the seatpost mounting arms of the rear rack. This puts the controller in open air to keep its heat down. It will reach temperatures of 135 degrees fahrenheit if stored enclosed. A home-made fender comprising of an extended commercial mudguard and cut-to-size flexible cutting board provides complete coverage from water coming up off the rear tire.
The front motor controller is an identical 35 amp KT, housed in the handlebar bag. This bag has had reinforced brass grommet holes placed strategically inside and out so cables can pass thru its inside compartments to the outside of the bag, without creating issues of splashing water (here again extended fenders help). The top of the bag is left zipped open and this keeps heat from becoming a problem. The front motor cable travels directly up and into this bag, while cables for pedal assist, brake cutoffs, display and throttle exit out either a grommeted side entry or out the open top of the bag. The bag itself essentially hides all of the front motor cabling rats’ nest, both by housing excess wire inside itself and via natural camouflage, providing a black backdrop to black cables running along and woven into its MOLLE exterior. Cables exiting and entering are carefully bundled together for neatness.
Is that a controller mounted to the front rack? Nope its a 5 amp weatherproof charger, with the cables housed in the dump pouch, just behind it.
The center triangle bag is stuffed mostly full with the custom-sized triangle battery. Like any triangle bag on an ebike, it also serves to hide excess wiring, and given the dual custom splitters for brake cutoff signals and pedal assist (one sensor signal is split off to both motors for simultaneous PAS power) there is plenty of wiring that thankfully remains invisible thanks to this bag, which seldom needs to be opened. The bag has forward and rear-facing cable holes that don’t suffer from water ingestion, again thanks to the fender setup. A capped XT60 charger plug is coming out the front of the bag just behind (and shielded by) the head tube, and this cap is removed and a charger is plugged in here to recharge the battery.
Display/Controls
Ergonomically, the cockpit is very well designed and reflects this being my third or fourth try at doing the job. There is one throttle for each thumb in easy reach, and both throttles are clocked so when fully engaged, the paddle is pointing straight down. If you hit a pothole your thumb doesn’t push thru and break the throttle. It slips off instead. The PAS panel is also one-per-side, and also within thumb reach without losing your grip on the bars. SRAM 9-speed shifters are in use, because a SRAM shifter gives you enough real estate on a handgrip (vs. Shimano) to stack multiple hand controls and still be able to easily reach everything.
Cockpit view. Notice the max speed reading on the top display. I used the gears and got a workout on the ride into the office that day.
Despite the duplicated motors and controllers, the displays are mismatched simply because I am re-using parts from older bikes no longer on the front line (in this case parts came off The Purple Thing). For this build I needed a new display and the KT model LCD8H was available, so I grabbed one. It is the same display as the KT model LCD3 above it, used for the front motor. The LCD8H is just in color and easier to configure.
And in case you noticed… yes this is a bike with Class 3/Speed Pedelec performance that has throttles. Reality is, though, the bike is designed specifically as a pedelec. Pedaling acceleration via PAS is plenty fast and is in fact (thanks to controller settings) a little faster than using the throttles. They are only put into use typically for a split second on take-off from a standing start while I regain my balance on the bike and settle in to pedaling. If I am crossing a 4-lane street, I am off the throttles before I get past the first lane while crossing and won’t touch them again until the next stop at the next intersection.
Power (too hot)
These two 80Nm motors have controllers feeding 35a to each axle provide giggle-inducing acceleration. So much so I found performance needs to be turned down for multiple reasons:
#1– (Safety). Come to a stop at an intersection. Acceleration is so strong from a stop, you leap forward so fast you are always the first vehicle that gets to the other side, and you’d better be hanging on. Thats fine if you meant to do that. If on the other hand you accidentally engaged pedal assist, you could be throwing yourself – literally – into the path of a car.
#2 – (Safety). Come to a stop at an intersection. Put your feet down, release the bars and take a drink or something. If you engage again (pedal assist or throttle) and forget to put your handlebars straight, your front wheel will shoot off in the direction its pointed in. Typically a bad thing.
#3 – (Fork survival). With this much torque pulling on the front fork, things start to happen that a bicycle was never stressed or designed for. A front fork was never designed to be pulled on hard, for extended periods or in sudden jerks. Especially not day after day for days and weeks stretching into years.
#4 – (Frame survival). This one was unexpected: Even though I am using a highly durable hand-made-in-USA frame, I still found it was straining under the repeated daily stress of stoplight-to-stoplight acceleration from the rear motor. Specifically I started to hear creaks from the rear triangle and dropouts. eek.
#5 – (Safety again for crying out loud!). I use fat street-smoothie tires in summer. Doing that with the motors unrestrained makes for about a half rotation of front wheel spin on full throttle, and maybe a 1/4 spin on pedal assist… and a goodly chirp out of the back, at the least (lots more if the ground is not clean, dry pavement). Thats fun for an afternoon showing off but more than that and its just plain dangerous.
Power (just right)
To slow down the bike so it accelerates at a safe rate on city streets, and doesn’t wear itself out from all the extra stress of doing this day in and day out, I utilize a setting in each of the two KT brand controllers that sets the power curve to ‘slow start’: C5=00 is undocumented on all but the newest KT display manuals. Where it is documented, it is listed as the most restricted of the three ‘slow start’ modes.
What this does is create an acceleration curve slope that is shallow at tip-in but increasingly steep as it continues forward. Here’s the crazy-cool part: Even dialed way down on both motors this bike is still typically faster than anything else crossing the intersection from a standing start. So you aren’t missing out on much in the way of fun if you want to pour on the amps. Its just safe, sane and controllable when its put on a leash.
Torque Arms (!)
I’m not going to get too deep into the specifics of this topic, but I will say if you use hub motors you have to use torque arms. Gotta do it. Thats for any motor that has ‘flats’ on its axle to allow their use (which is almost all of them). It is true many motors do not need torque arms because they are of such low power. I will say having suffered the consequences of not using one, its WAY better to be safe than sorry and just go ahead and install them regardless of motor power.
What could happen? If you don’t use a torque arm, the force of the motor will overwhelm your bicycle’s dropouts and the motor will “spin out”. That means your steel dropouts will not be able to contain the motor’s axle, which will spin (instead of the motor casing spinning) and when that happens the dropouts spread. Your frame or fork is effectively destroyed and unsalvageable at that point. These 750w, 80Nm motors are right on the edge of demanding two torque arms. For sure they need one. I have used two on the front motor and one on the rear, where the stronger rear dropouts are much less likely to have an issue.
Gearing
Last but not least… take a look at the pictures on this page and you will see the biggest front chainring ever on a fat bike. Look to the back axle and you may be looking at the smallest cluster. And the derailleur is a mid-length cage, to boot. Fact is, this bike was geared to be pedaled fast on the street, not overland on trails as is the norm for fat bikes.
The front chainring is a 50T ring, while the rear cluster has an 11T small cog. Frankly I forget the size of the biggest cog because I never use it. Its 28T… Maybe 30. And since the hubs on this bike are the motors, powering the bike thru the axle, not the drivetrain, gearing is largely useless unless I want to pedal faster while going slow. This almost never happens because this bike should not be taken on pedestrian paths or similar where such slow travel is necessary.
Redundancy
For a daily driver bike that is transportation, not recreation, you need to address many areas to ensure reliable, day-in, day-out operation. There are many issues addressed on that topic with this bike, but I’ll only touch on the AWD-specific ones here. In a word: Redundancy. If you do a general overview of this bike’s propulsion systems, you will see almost everything but the battery is a separate, independent system. None of this is accidental or done because I was forced to do so (you can buy controller solutions that reach out to two motors at once, for instance). Its done this way because its better. Dual throttles are better. Setting PAS independently per wheel is better than combining the two. Even two different displays let you focus on different bits of each (although that one I could do without if push came to shove).
Redundancy on a dual motor bike can be a big benefit. I’ve had one unfortunate lesson in this: I went over the handlebars and slammed straight down on the pavement, cracking some ribs. I also bent my front fork (just a little) and smashed my rear throttle, among other things. That broken throttle disabled the rear motor despite all other components being in working order. I was able to limp the bike home without pedaling, which I really needed given the cracked ribs and various and sundry other minor injuries.
This is one more reason by the way, why I want throttles on the bike. If I am physically unable to pedal I want to be able to get me and the bike home, or to the emergency room as the case may be.
I like to build top-quality-component ebikes from the frame up. Quite a few of them are dual motor or AWD or 2WD or whatever you want to call them. Why would you build an AWD ebike?
Well, I could spell ‘ebike’ and that was about it. I had a solid background as a lifelong cyclist, but I went over to the Dark Side and started riding ebikes. I had been working on my own bikes for most of my life and I was pretty good at that part.
So, as an experienced cyclist but a newbie ebike owner I came across a bike built by my (now) friend Houshmand Moarefi, who is the head honcho over at Ebikes USA in Denver. He took the same model of rear-hub-motor ebike I had, upgraded the rear motor, then added a front motor, controller and surrounding bits to make a badass AWD e-fatbike. He posted his creation on the Interwebs.
Figure 1: Houshmand Moarefi’s 2wd Sondors Original. Want to know what dual-motor is good for on an ebike? Just look here. He still rides this bike and you can see it on display at Ebikes USA in Denver.
After seeing the bike online – and peppering Houshmand with questions – I did what everyone on the internet does: shamelessly copied his idea. It is pictured in Figure 2 below. This was taken the night I completed it, moments before I opened that garage door and took my first ride.
Figure 2: AWD by Matt… Version 1.0000. a.k.a. The Colonel (“Colonel Sondors”). How much did I have to learn about doing AWD right? I’ll have to make a list.
Its a good thing I took the picture, as 15 minutes later I broke it. I got it fixed and it gave me years of service, but thats another story entirely. Suffice it to say in that pictured moment, we see triumph and despair occurring almost simultaneously.
What are we in for, building one of these things?
First… “Whhyyy?”
Why put two motors on an ebike? Well… “because we can” works. But lets do better than that.
Is it even possible?
Not so long ago, internet experts in the DIY ebike crafting community would tell you all about how a powered awd ebike could not even function in the first place.
The powered wheels would fight for supremacy between each other.
It is essential to match the power to both wheels but impossible to do so.
Even slight differences in wheel circumference between the two would make terrible things happen.
blah blah blah
So, I was being told it could not be done after having put thousands of successful miles on a bike that could not exist. A lesson on the value of internet experts. Only value the advice of those who have done the work and actually know things.
I don’t want to get too deep into a litany of refutation on common mistakes, but I do want to clear up a couple that come up the most often. All three, really, are more or less re-statements of the same misconception:
Matching Power (current) to the Wheels
This is a common worry, but not a real one as you will discover moments into your first ride. The concern is dissimilar power levels cause problems. They don’t. Tailoring power front to back as conditions change is a major benefit to AWD. In simple clean/dry conditions, all that will happen is the wheel that gets less power doesn’t work as hard.
The easiest way to understand how this is: Geared hubs freewheel forward. So the same thing happens if you have no motor on the back and you are, say, going down a hill with a front motor. The watt output of the front motor decreases as gravity ‘powers’ the speed increase (or you pedal your little heart out on flat ground). Likewise, differences in circumference are a non issue. This is true in bikes with slightly different tire sizes, but is most visibly proven with the in-service bike pictured below.
Figure 3: Different types of motors with perpetually different outputs… and totally different wheel sizes. It still works great.
Contention
Here again, one ride will lay this concern to rest. Two motors will not fight for supremacy with each other despite differing power levels. Partly because of the geared hub’s ability to freewheel. You should take it for granted you will have different power levels on each axle. I commonly keep low power on my front wheel (I will expand on why further on) but for my hub+hub commuter I often just go full blast on each motor and pedal up over top of it. In that instance, with two big motors giving it their all I only very rarely feel a bit of a shift in pull vs. push and it is very minor. Another technique on that bike: 5 levels of PAS on the rear wheel plus 5 on the front means that – in good conditions where I do not vary the power for safety – I have PAS with 5+5=10 levels. As I want more I ratchet up the rear a notch, then the front, then the rear and so on never giving all PAS power to just one wheel.
One Throttle/Two Motors
You don’t want this. You can have it but you are selling yourself and the platform short if you go to the extra amount of trouble to make it happen. I will get into some real world specifics of why this is later on. The short version is if you unify the throttles or even work harder to unify PAS power levels to the two wheels you will be introducing problems with traction and control. You want to keep your control granular. It won’t be confusing or difficult!
What About Two Direct Drive Hubs With Regen?
What I said above doesn’t apply. If you expect to use regen on a twin-DD-hub AWD bike then you are talking about a whole different animal in terms of two hub motors coexisting. I know its been done, but I have never done it personally. I will let some other pioneer on the trail take the arrows in the back on that one (I suspect: regen can be used on the rear but not on the front… or just don’t do regen at all with DD hubs).
A final point: Years into having AWD bikes in service, there are now numerous commercially-produced examples in plain sight. The arguments that it cannot be done have melted away now that so many have obviously done it.
Figure 4: The Purple Thing. Built after the death of The Colonel (cracked frame not related to AWD)
So YES you can do AWD. The question is are you doing it right? Well, thats a whole ‘nother thing.
Whats the Up Side?
Take a look at Figure 1 for the most obvious example: All Wheel Drive on a bicycle is every bit as good of an idea on a bike for the reasons it is a good idea on a car, truck or ATV. On other vehicles, just putting more power to your back wheels is not anywhere near as good of a solution as putting power down to all wheels. It is the same on a bicycle, but so few have done it, the result is not considered to be the obvious no-brainer it is on other platforms.
If conditions are sub-optimal, as in rain, snow, mud, riverbed rocks, hillsides and whatnot… AWD on a bike gets you through it easier, across the board. If conditions are ridiculously bad, AWD can get you thru things you thought were impossible to ride. Oftentimes so easily you stop, look back and wonder how the hell you just did that.
The range of things that you can ride through just got a lot wider.
If on the other hand conditions are just dandy – say, a smooth, flat, dry paved street – having both wheels deliver power to the ground is again an improvement for all the same reasons it is better on a performance exotic car. Powered traction is distributed across twice as much rubber to the ground. Everything just works better.
And since the improvement makes for a qualitative, but drama-free result, its really hard to describe other than to say ‘everything just works better” or “this is how it was meant to be” … which do not help much when explaining AWD to skeptics. Nonetheless… the nebulous, big-brush-stroke description is accurate.
In terms of acceleration, doing it with AWD vs. RWD is a very different rider experience. You aren’t being pinned to your seat, nor is your body wanting to slide off the back while you hold onto the handlebars for dear life. Instead you get an amazing rate of acceleration, but it is smooth and – again – without drama. The feeling is of it being effortless for the bike to do what its doing.
Mechanically there are benefits as well. If you are keeping tabs on the amount of heat your motor generates, you’ll find gunning one motor around will get so hot you may not be able to touch it for awhile. Not so good for longevity, especially if it has nylon gears inside. But: Run two geared hub motors as a team to achieve the same performance and by some miracle the two don’t even get a fraction as hot as did the one. All of a sudden a motor that was working itself to death isn’t even breaking a sweat, and you’re going at least as fast and as hard.
How is this possible? In May of 2020 Grin Technologies did a detailed technical analysis of multi-motor ebikes. They explain how this is possible, complete with the technical details on why it happens. Its well worth a watch if you are interested in taking a deep technical dive on your AWD ebike options. I have queue’d up the video in the link below to the exact spot where he explains the heat reduction.
Another issue not generally considered is redundancy. With two motors, if something bad happens on your ride and you lose a motor, you still have another and can limp home on it. I learned this the hard way once when I went over the handlebars on my twin-hub Great Pumpkin. I smashed one of the throttles and disabled the rear motor completely. I managed to roll home on the front motor without needing to pedal. With freshly cracked ribs that was exactly what I needed.
Whats the Down Side?
AWD is not all sunshine and roses. There are down sides. Most of them only affect the bike builder. But a few do affect the rider, so we’ll look at the negatives from both perspectives.
For The Builder…
Put simply, AWD on an ebike is one hell of a lot more work. There is so much more you have to keep track of. So many more wires that have to be hidden.
Fig. 5: Custom brake cutoff splitters and extensions for sending signals to 2 controllers
You have to address the issue of brake cutoffs going to two separate motors simultaneously. Pedal-assist to two motors at once is a beautiful thing. But only for the person riding the bike. For the builder it typically means customized controller settings and maybe even a little fabrication to get a sensor signal to two motors at once.
Fig. 6: PAS splitter cable (one sensor –> 2 controllers)
Battery power? You’re going to need a big battery, and it needs to deliver more power than pretty much any regular ebike battery available on the open market. So you either have a single custom pack made or kludge together off-the-shelf packs and suffer through the weight and space issues that go with them.
Fig. 7: Cutout sized, marked and photo sent to the battery builder. All thats left is to drain my bank account.
What does a front motor need in terms of structural support? You’d better think that one through. NEVER use a suspension fork in an AWD build. Your motor can literally pull the thing apart. Whoever designed a bicycle fork never expected a powerful motor would be pulling on it for extended periods, or in sudden jerks. Thats tough on a chromoly fork but they can handle it. Its typically too much for an alloy fork (aluminum is nice and light but doesn’t bend: it breaks) and it is definitely too much for a suspension fork that has 2-piece blades that can be literally pulled apart.
Not to mention fork dropouts. A hub motor must have torque arms attached that prevent the motor from ‘spinning out’ (That is how I broke the Colonel on its maiden voyage; destroying its fork dropouts). You generally cannot use quality torque arms on a suspension fork due to its physical construction. If so, the dropouts have to endure 100% of the punishment and… newsflash … they may survive today but they won’t have the kind of long life they would have had without a motor axle trying to tear thru them.. Internet discussion groups are chock full of pictures of DIY builds where someone used a front hub motor and their suspension fork’s dropouts snapped clean apart. Even with a torque arm.
We’re not done with the front fork yet. Regardless of construction, that pulling on it can loosen your headset at an alarmingly fast rate depending on your power and acceleration levels. If its a problem you have, you will want to think of ways to keep that headset in place (psssst… use two star nuts) and while you are at it, make sure you use a superduty headset with steel races. And a serious mtb stem that clamps the crap out of your steering tube.
You can google “broken ebike fork” or just follow this link (one of many) on Endless Sphere to see more electric motor + fork carnage.
So… How do you get away with using a front suspension fork, then? You see people do it with front-motor bikes. Assuming they thought the job through and are not just future emergency-room visitors, its simple: use a very low power motor. Or neuter a powerful motor and trust the buyer won’t know any better because hey… nobody has any actual experience with these things so you can give them just a little power and they will still be thrilled.
So… to build or sell an AWD bike its a whole lot of work for the same result (a single finished bike). Its no wonder AWD bikes are not common, and when they are up for sale, the seller wants a high price. Assuming they did their job right (never assume), a lot of work went into that bike.
Fig. 8: Wires everywhere. I have to figure out a way to hide all this…
For The Rider…
Fortunately, the downsides of AWD are minimal if all you have to do is ride the bike. But they do exist. All of the negatives can be eliminated if you just realize this bike is a new kind of animal and take it easy when starting out. So… learn how to handle the increased traction, power, and the subtly different behavior.
Dual Throttle
If your bike builder did the job right (I’ve said that two times so far and not by accident), you have two throttles – one for each thumb – to let you apply power granularly to each motor as the needs of the moment come up. Thats a new feature you will need a bit of time to learn how to take best advantage of. The basics of this will be learned by the time you have traveled about one city block. The finer points will take some experience – not a lot – to figure out.
Holding down the front throttle in a turn has the end result of elongating your turn radius (this is about how you naturally ride, not how the bike handles… but it still happens). You cannot take a turn as sharply if applying front throttle, and could wind up smashing into the center median in a right turn in traffic, or the curb in a left turn thru an intersection. There is an easy solution: stop pedaling, release front throttle, turn in, re-engage front throttle just at turn-in so the slight delay will engage the motor right about at the moment of corner exit. Leave rear throttle engaged throughout the turn if you can safely get away with it). That turn procedure all takes place in the space of about two seconds. It will become second nature in short order. But it has to be learned. Now… thats how you hot rod your way thru a turn. You won’t want to do that all the time, and mostly you will go thru a turn no differently than you do on any ebike.
On singletrack/trails, less power to the front wheel is more. Rip down a trail, hit a root and the front wheel bounces up. If it comes down pointed in a different direction than you are headed, your now-powered front wheel will shoot off in that new direction if its going full blast. Keep front motor pedal assist power low – much lower than what you have set for the rear. Then when the inevitable happens its easy to deal with. I’ve found pedal assist dialed down in the 200-250w range is best. If you decide you want more front wheel power at any point, a dab of throttle will do ya. You know you are overdoing it if you get any level of wheel spin in the front.
You are no longer the slowest thing accelerating from a stop at an intersection. So if you are not the first vehicle in the left turn lane, Your instinctive use of full throttles to both motors will rocket you right into the rear bumper of the car in front of you. This is an easy fix. In a left-turn-lane situation, initially use only rear throttle, then add the front when the car in front of you starts to pick up speed. Dial it back again as that car completes their turn and lifts on their own throttle before straightening out. Or you can just hit the front throttle for a split second to get yourself rolling from a stop, then drop it and let PAS manage the rest.
Clearly from these examples, manual AWD acceleration (separate from pedal assist) is a learning process. A dual throttle is a big part of getting this down pat without needing to dumb down the bike’s performance.
You can run an AWD bike with a single shared throttle, but doing so means you will be lifting more frequently and when you do its all-on or all-off. You will lose the ability to decide for yourself what happens and the result is more jerky and less refined.
Battery
If your bike builder did the job right (there it is again), its got a single big battery with a high capacity Battery Management System (BMS) capable of handling the peak and continuous loads of both motors running together. For the rider who has such a setup, the only thing necessary is to set aside enough quality time on a charger to get this bike up to snuff to carry the day’s ride.
Fig. 9: The Purple Thing was … Gen 1.5. Rear motor battery in triangle, front motor battery in the rear rack pack. Front controller in the handlebar bag. Rear controller is in open air under the seat on the rack stays (best for cooling).
For the rider not lucky enough to get a proper battery, that means – at the least – putting up with dual batteries in positions that reduce carry capacity. The rear rack typically gets the duty for one battery in a dual-pack system, so whatever your rack’s capacity was, take off 10 lbs and only use the sides. You may also have to deal with charging the two batteries separately, which is a big drag on convenience and turnaround. You *will* have days where you forget to go and switch the charger to the other battery. Speaking personally: Been there, done that.
Fig. 10: One of my Gen 1.0 iterations with the front motor battery in the bag under the handlebars. Don’t ever do this (but the dual kickstand worked *great*).
Maintenance
Two motors = two sets of service intervals. In practice this should not be a big deal, but fair is fair – we have to count this as double the effort on motor maintenance. This is the part where the direct drive hub people all jump up and remind you for the 100th time that they need no maintenance. You will also get slightly faster wear on the front tire, now that its powered.
Commercial Feasibility
I’ve made it pretty clear what I think a proper feature set is for these sorts of bikes, based on the fact I started doing it a while ago, and I’ve had the opportunity to work thru a variety of designs and iterations to find out what works best.
Dual throttle
Single hi-current battery low and centered
Redundant, dual controllers and displays
NO front suspension
Shared signals from sensors
All you have to do is look at what is out there commercially to see none of the bikes out there adhere to this. When I look, I see the sort of feature sets – and mistakes – from when I first started kludging AWD bikes together. The reality is, though, from a commercial perspective we are unlikely to make much headway forward in the near term. Why?
Money… thats why. What I describe is maximum-cost given its redundancy. Its also darned expensive to build an XL battery with a high capacity BMS, and in addition to that, there is the issue of minimum order quantities from component/battery manufacturers. I don’t see it happening unless a manufacturer goes on a mission to sell a bike that is thoughtfully designed to be a cut above the rest.
More likely to happen: Development of a suspension fork strong enough to withstand the pull of a front motor over the long haul. It remains to be seen if ANY of those in use now on commercial AWD bikes is going to last. We’ll have to see if product liability issues (and injuries) ensue from whats in use now, or whether the sellers have de-tuned the front motors sufficiently to let those forks survive. But down the road, this is definitely something that could successfully evolve.
Something that came on stage right about the time I published this article is the Eunorau Defender-S on Indiegogo. That is a full-suspension bike, so there’s the front-suspension concern. Given its late-2021 delivery date (plenty of time to figure stuff out), the fact that the vendor is going nowhere near any obviously phony claims, and reliable people who know the company are giving it a serious look, this AWD bike may be something of a landmark for the species both in price and thoughtful use of components.
I would be remiss if I did not mention the AWD motorcycles, bikes and ebikes developed by Christini, where they have created a unique, robust, mature – and patented – system to share the power from one motor (rider or electric) to two wheels via mechanical linkage. Lets say that a different way so its clear what they have accomplished: They tap into the power of a single motor (either the rider or a BBSHD) and use that to successfully, reliably power two wheels. Its pretty neat stuff.
What does all this mean for the DIY ebiker? Well, the tools and components are out there for you to build your own, and do it considerably better or less expensively (or both) than anything available in the commercial marketplace.
Fat chance you’ll see a tree-climber like this in stores near you anytime soon.
Wrapping It All Up
The best way to see what good can come from an AWD bike is to look at some representative examples. I have chosen three that work very well for me, and do so in very different ways. Because we’ve gotten to a good place to pause with this post, I’ll do so and point you to the individual case studies that should be linked together in the menu at the top of this post
Some Bafang BBSHD and BBS02 programming tutorials say Speed Meter Signals must be set to 1 or bad things happen. They are right. They are also totally wrong.
This is going to be a quickee post to show off a little spiff you can do on a Bafang mid drive, and point out something wrong I see in some tutorials or forum posts about Bafang BBSHD / BBS02 settings. Specifically:
The Speed Meter Signal
Put simply: It does not have to be set to ‘1’. But I am getting ahead of myself. Lets start from the beginning:
At the root of the matter is the BBSxx Speed Sensor. If you buy one as part of a kit, or on its own, this is what you get for roughly US$20:
Figure 1: L to R: Sensor magnet, sensor base, sensor and underneath, the two screws used in the install
The speed sensor magnet attaches to one of your spokes. You attach the sensor to your chainstay (usually) and position it so the magnet passes close to it as the wheel rotates. The sensor detects the magnet’s passing and calculates your speed, via a rotation count and knowing your wheel diameter via a separate setting.
Figure 2: The speed meter installed on the chainstay.
So if you buy the typical sensor, you get one magnet, one sensor, and you need to set the Speed Meter Signal to ‘1’. Is that setting because you have one speed sensor?
No. Speed Meter Signals counts the number of magnets. Not the number of sensors. Each magnet is a signal. Got one magnet? Set it to 1. Got two? Three (for a 36-hole wheel)? Four? Change the setting accordingly and it works great.
Figure 3: The Speed Sensor settings from my Luna Black Box, with the setting in question circled.
Why do we need more than one?
The one magnet works pretty good as it is, so nobody really gets too deep into this. Plus nobody sells Bafang speed sensor magnets by themselves. So to do this you are talking about roughly $20 per magnet because you have to buy a whole speed sensor assembly.
I have found these can just be tightened onto a spoke by hand, and they do not need any thread locker to stay tight (adding some Vibra Tite would not be such a bad idea). Reportedly these magnets work over a much greater distance than their Bafang cousins, which is another benefit.
Get To The Point!
Fine here it is. Look for the speed sensor magnet in the picture.
Figure 4: How many lights do you see, Picard?
There are four lights magnets on this wheel. One every 8 spokes. I have the Speed Meter Signals reading set to 4. The improvement is not earthshaking but I do get the following:
My speed reading on my display updates faster and more smoothly. Quadrupling the signal input is a good thing which is not a surprise.
The Cateye magnets are smaller and lighter by a fair bit than the Bafang magnet assembly. This results in the wheel getting thrown less off-balance than when using that big heavy Bafang doodad (even if you place it opposite the valve stem to even out the weight distribution).
Four magnets placed equidistantly around a wheel make for a more balanced wheel spin. Its minor. But when spinning the wheel with the motor when the bike is up on the stand the lesser amount of shaking is noticeable.
Using just two sensors (the 2-pak of Cateye sensors is only $9.95) gives a noticeable improvement as well. Enough that 4 sensors is not noticeably better or worth even the minimal the cost/effort. I can’t help but think that two magnets means two points of potential failure rather than four. This weekend I’m going to go back to two magnets.
So…
You can take this tidbit as useful in a couple of ways: A cheap, lightweight, stronger magnet replacement or a way to get a better speed signal to your display.
Its not a big improvement, but it is a nice little one.
One of the most notable features of this Big Fat Dummy are its handlebars with the integrated basket made of thick, hollow alloy tubing. At first glance, these are nothing more than EVO Brooklyn integrated-basket handlebars. Here’s a factory-stock picture of them.
Now lets take a look at the ones on my Surly Big Fat Dummy. Notice a difference?
Figure 1. Hint: Look at the grips
The grips give it away: I extended the handlebars so now they have a width of about 810mm. I am using ESI Extra Chunky 8.25″ grips to cover the extensions and give me an extra-long gripping area, suitable for multiple hand/seating positions (choke up and hammer it, sit up and cruise). Just like on a pair of Jones bars, the brakes can be reached from any position on the handgrip.
The grips give something else away: the bar extensions have a smaller diameter than the stock handlebars. At first I planned to use the extension you see in the pics below as an internal sleeve coupler between another bit of tubing, the same outside diameter as the handlebars. After seeing it in place and thinking this ‘coupler’ had potential on its own, I covered one side in a grip to see what it felt like. The two diameters worked for me and I decided to stop there.
I like the lesser diameter as a sort of change to the handhold. Good for longer rides where I want to vary my grip to reduce fatigue. The wide outer hold is better suited to comfy cruising anyway, so between that and the added thickness provided by the fat ESI grips: The lesser diameter section feels normal. The point of transition between the two diameters is also another form of handhold variation. It is just one more way to grip the bars differently on a long ride to change up what part of my hand is getting pressure.
What about the bar extensions themselves?
They are a bit of aluminum bar stock whose outside diameter is very near that of the inside diameter of the handlebars. Some fairly pricey stuff can be found at specialty hardware sites. I stumbled upon pre-cut bar stock with the right OD; already cut in the perfect length, so I didn’t even need to put a saw to it. (I did chamfer and bevel the inner and outer edges with the same tool I list in the Big Fat Wideloaders post). I bought two of these and that part of the job was done.
Specifically, the material is 6061-T6 aluminum bar with a 0.625″ (5/8″) outside diameter, a 0.375″ inside diameter (0.125″ wall thickness). Each bit of tubing is 10″ long. On the off chance its a link that will live on (its live as of today, several months after my purchase), here is what I purchased.
How did I affix it inside the handlebars? A combination of things hold these extensions firmly in place:
The inside diameter is a close fit but not a tight fit. I wrapped a single layer of silicone tape around the inner bar in two places with a gap of a few inches in between. Just enough to make it a seriously tight fit.
I spread/glopped some JB Weld around the outside diameter of the inner bar, in between those silicone tape wraps, before insertion. That makes for a bit of a seal for the application of the JB Weld and ensures during insertion it builds up into enough to fill the gap between both bars.
I inserted the bar fully and then used a 2-lb sledge to make sure it was for-sure seated inside the handlebar.
Stretching/installing the ESI grips over the assembled, extended bars provides, in and of itself, a strong hold that prevents movement.
One last note: Even at an 810mm width and extended grip length, the ESI grips are just a skootch too long for this bar, considering the controls I have to mount on whats left of its straight portion. I turned that bug into a feature. The ESI grips are so substantial they are good as bumper pads. To supplement that, I tightly rolled up some white silicone tape (the same stuff I used in giving the bars a tight fit) and used that as a bar end plug. The roughly 3/4″ of overhang is now a substantial padded bumper, useful when I am leaning the bike up against something. You can see the bumper in Figure 2 below.
The Double Stem
Figure 2. Going up. The stems are angled up in this pic for an elevated bar orientation.
Wait… what? A double stem? What the hell is the thinking behind that?
So, here I am building out this Big Fat Dummy with these basket-case handlebars. I have used them before, on Frankenbike. On that bike, the bars could shift down if you were standing up, honking on the pedals and putting strong downward pressure on the bars. Knowing this can happen, how can I get around it? Would using a higher quality MTB stem do it? Then I realized a)I had an uncut steerer on my Bluto fork and b)the handlebars have two mounting points in their design.
The idea was to use one or the other. But that long uncut steerer might just let me use both (spoiler alert: it does).
So, as usual I tripped and fell into a functional and eye-catching solution. Use varying spacers in between the two stems so they space apart exactly to fit the two mounting points. The lower 25.4 stem mount point needs a 31.8 spacer around the bar. Also, the easiest way to limit the variables in play is to use identical-model and -angle stems and simply vary their length. I used Funn Stryge stems in 60mm and 80mm.
In Figure 2 above I have angled both stems up, giving the most upright position possible. Later on, I flipped the stems to a down position to give more lean-over (clearly these bars have a significant rise built into them so seating position is still fairly upright).
Figure 3. Going Down. Both stems are mounted upside-down for a lower handhold. Just reverse the front plate so that part is right-side up.
In my final tinker with the stems, I changed their orientation once again: The lower stem is still pointing down, but the upper one is pointing up. This still keeps the bars oriented in the ‘down’ lean-over position, but the position of the upper stem moves further down the steering tube to achieve the same bar angle it had when it was matching the lower stem as seen in Figure 3.
Whats the point of doing that? It uses less steering tube. As you can see in the pics above, I am using 100% of the Bluto’s uncut tube. Making this flip and exposing more available steering tube enables a change to a Wren Inverted fat fork, which has a 20mm shorter uncut steerer…. with this change I would use 100% of the Wren tube, should I ever find another home for the Bluto.
Reinvented Wheels
The Surly My Other Brother Darryl wheelset that comes with the Bliolet Big Fat Dummy is very good. It can take quite the beating. I certainly have never been able to throw either of them out of whack. However, I wanted summer and winter wheels, the ability to go tubeless, and have wheels as strong as possible. Additionally, the MYOBD wheels hold on to tire beads so tight it is effectively impossible to get at a tube to repair it on the side of the road. That had to change.
SIDEBAR: If the MYOBD rims are tubeless-compatible as claimed by Surly, mine certainly are not. The rims are pinned and not welded. And both of mine leaked at the pinned seam on the edge just under the bead – a place you can’t tape. I personally don’t see how they can be used tubeless unless you get lucky and those pinned rims are perfectly manufactured. Mine were, and are, great tubed wheels but they can’t be used tubeless even when its been done by professional LBS techs who know what they are doing. I failed. They failed. The rims don’t work tubeless.
With that said, lets focus on the wheel build. I settled on the following components:
DT Swiss 350 Big Ride hubs
The DT Swiss 350 Classic is just that. A reliable classic. In particular, the rear hub is acknowledged by DIY builders as extremely durable when paired with a high powered mid drive. Couple the ratchet engagement mechanism to the steel cassette body option that DT offers and you have the core components of a bulletproof drivetrain. DT even makes the 350 Hybrid hub that is reinforced still further for tandem and ebike applications. Sadly, its not available on the fat bike Big Ride variant. But a plain 350 with a steel body is still unstoppable. I know because I have used one on my 2Fat build for some time. The 2020 parts shortage made finding a front and rear hub an adventure – I got the rear in Poland and the front from the U.K. … But I got them.
Alloy on the left after 1500 miles. Zero miles and steel on the right… After 2 years it still looks that good.
Nextie Wild Dragon II Rims
This was a tough one. These are REALLY expensive hoops at over $300 each. However, they are also a known quantity as I own another set on the Stormtrooper (those wheels with their matte 3k finish are the header image for this blog). The standard version (not the Elite light weight) have a load capacity of 250 kg. Nothing else on the market can touch that. Also they have a center channel I know from experience makes the difference between getting the tire off the rim on the side of the road, and not being able to do so (that would be the MYOBD’s). Lastly, they are a nice compromise of 90mm, which I hoped would allow me to lose only the highest rear cog on my 11 spd cluster. Turns out that was a correct guess. Others who go 100mm lose the top two.
The Nexties check all the boxes. It boiled down to whether I was willing to spend the money. After some time hemming and hawwing, I surrendered and spent the big bucks.
<takei>”Ohhhhh Myyyy” </takei>
I did 3k matte finish last time. This time I upped the bling factor – just a bit – and went 12k matte. And holy cow are they ever gorgeous. They fit the bike perfectly with that deep dish construction making the fat tires the fattest fatties in Fatland. As it is, this beast of a bike already makes a serious visual statement. The wheels dial the message volume to 11.
With the above said, you might be under the impression that the look of these wheels contributed to my buying decision. I am outraged anyone could consider such a thing.
… and they’re waterproof too!
Sunrace CSMX8 Wider Range Cluster
The original Surly-spec’d cluster is a Sunrace CSMS7 11-40T. Even though the Surly BFD is not sold as an ebike, that is the perfect 11 speed cluster for one. It is all-steel, bolted together into a single 1-piece unit and has steel spiders inside. As usual the heavier, cheaper steel component is the good one if you have an ‘e’ in front of ‘bike’. Finding an 11-42T version of that cluster would have been perfect… but alas thanks to the 2020 parts shortage, I couldn’t get my hands on one. I settled for the CSMX8, which is 11-42T and also uses steel cogs. Its in 3 pieces and uses alloy spiders. Not ideal on a mid drive, but its still a respectable bit of kit. Why did I want a wider range cassette? because I knew other Big Fat Dummy riders who went to wider rims and tires lose their two biggest cogs. Expecting this, I wanted the biggest cog I could still get to. So: wider range cluster.
As it turned out, the 90mm rims and 4.8″ Vee Snowshoe XLs only cost me one cog. So while I cannot use the 42T cog without rubbing, the 36T just under it is no problem. That means I only lost four teeth off of my former 40T inner cog, and I have a 10-speed instead of an 11. I’m fine with that.
Sapim Strong Spokes
Here is the one place I compromised. I wanted DT Champion 2.34 spokes. In the age of lockdown-induced bicycle parts shortages, that was just not happening. Nobody had enough spokes in the three lengths I needed … worldwide. Actually I did find stock in a bicycle shop in Germany but they refused to ship to me because of the then-severely-extended ship times of 10 weeks-plus. DT Swiss themselves said forget about it until at least 2021. Casting about, I talked to other strong players including Phil Wood. Every time, I struck out. Eventually I did find a small local bike shop in another US state who had Sapim Strong spokes and could cut them to the sizes I needed in-house. The 2.34 Champs would have been stronger, but the Sapim’s are plenty strong themselves. I don’t expect any issues.
Orange Seal Valves and Whisky Tape
Last but not least: The valves and the tape. Whisky tape is good stuff – a bit wider than most alternatives – and I was able to find a big roll, so I had plenty of extra socked away for my attempt at converting the MYOBD rims to tubeless (which as noted above… failed). I chose the Orange Seal 60mm valves because they have something a lot of valves do not: A metal bottom. Why? the metal bottom provides a hard surface that the valve gasket can firmly smoosh up against. There’s no way for the valve to pull thru. Its also less likely to spring a leak down the road when you manhandle the valve putting air into the tires. This last issue plagued my Stans valves on a different bike, until I replaced them with these.
You get everything but the kitchen sink in the bag with the Orange Seal valves, including a nice core-remover that screws onto the valve itself so it can’t get lost.
Phat Tubeless Tires
So… on this bike… tubeless is where its at! The Nextie rims coupled to Whisky tape seal right up. The Vee Snowshoe XL’s I put on (I have had them in the garage for a couple years and it was time to use them up) sealed to the rims so well I didn’t really need any sealant to finish the job. They held air for days as-is.
But of course I used sealant. And as I have mentioned in earlier posts, after discussion with the manufacturer and some great experience with it as a tube sealant, I used the recommended 16 oz(!) of FlatOut Sportsman Formula as my tubeless sealant. Application is easy via adding a presta adapter to the end of the integrated hose in the bottle lid. Once in the tire, they hold air for about… 5 (five!) weeks before its time to air up again.
And since I set these tires up, after a few months, I had the worst-case experience with respect to finding out whether FlatOut actually works to seal up tires.
Want to see a cyclist poop his pants? Punch a line of a half dozen of these in his back tire. Then tell him to hop off the saddle and go look…
Yeah thats right. So I go to Home Depot and load up on all sorts of crap. My Great Big Bags as well as my upper deck are pretty much full and I am chugging home. Suddenly I hear a tickticktick behind me and I know thats not good. I jump off, look down and OH.MY.GOD I see a row of about six roofing nails stuck deep in my back tire. As if thats not bad enough they are off to the side in the vicinity of the sidewall (the ticking was a nail head hitting the frame as the wheel revolved). Not thinking to save the nails for a future photo shoot, I pulled them out and cast them away. When doing that I saw the tire knobs pull away from the tire thanks to the damage from the nails and of course the hissing got worse. Having lots of sealant in the tire, I did what I could to lean the bike over on the side with the holes and roll it down so the goop could glop into the holes and save my bacon.
The hissing lessened but didn’t go away.
26×4.8 tires inflated to a street-legal pressure of 18 psi have a lot of air to give, so I jumped on the bike and got rolling fast; again with the idea of letting the sealant spread and seal. I got maybe a block before the lessened but continuing air loss meant it was time to stop and refill. Here’s where having the lightweight, emergency electric bike pump made all the difference. In short order I had the pump connected to my tire and battery and it began noisily refilling the now almost fully flat tire. Once the tire got reasonably firm I disconnected, stuffed the pump into the kangaroo pouch and got rolling, all the while hearing hissing, still. I repeated this process two more times on the way home. After the third refill, the hissing stopped. FlatOut sealed a massive series of holes and today, weeks afterwards, the tire is still holding that same amount of air.
It remains to be seen if the tire can be considered reliable for long term, long range use. I have been riding other bikes in The Pacific Fleet recently until I can take the time to do a full post mortem. But bottom line: FlatOut got me home and averted certain disaster. It gets my enthusiastic seal of approval.
The Bag Bumpers
Problem: the Great Big Bags are so big, they exceed the length of the frame structure. The padding keeps them from flopping around, but they can still curve inward and, on the drive side, touch the chain which is very close by. That chain is a chain saw on the fabric and you’d better not let it contact the bag for long. Also in the rear the bags can be worryingly close to the tires – still 2-3 inches away but it would be nice for them to keep their distance period.
Solution: Re-purpose the existing M5 bosses that Surly used for the stock Dummy Bag mounts. Attach a 36″ metal strip, whose function is pretty obvious just looking at it:
Figure 1: Initial test fit. This fit uses smaller washers and the strip is upside-down as noted below.
Pretty straightforward stuff. Whats not so straightforward? I think Surly did a pretty solid job of engineering this frame so its sturdy where it needs to be and flexible when it needs to be. They don’t need me re-engineering the give and take this frame was designed to deliver under load. So the challenge is to create a rigid structure that keeps the bags from intruding into the wheel well, but at the same time does not provide unexpected structural rigidity.
A stiffer frame sounds great, until you realize you are adding rigidity selectively. If flex is a part of the frame design, then its going to happen one way or another. I would rather it be distributed as the manufacturer intended rather than restricting all of the forces to exert themselves in a new spot, in a way the designers didn’t anticipate.
So here’s how we do that: first and foremost, I drilled an oversized (M10) hole at the front anchor point. Additionally, I sandwiched the connection in front and behind with rubber washers that themselves are captured on both sides by stainless oversized washers.
That big hole is off center on purpose. You hang the strip so it lies roughly centered. Then it can still flex without hanging near its edge (Figure 1 is a test fit and its actually upside down in that pic).
Also note the steel washers above were swapped out for wider ones to fully capture that rubber washer in between.
Just an oversized hole doesn’t fully allow the frame to flex as designed. You need a long slot in the back to further allow unrestricted frame movement. I created this by hand using a time-tested – and ugly – method:
Mark your material with a Sharpie.
Drill a line of pilot holes with a small bit. Yes it looks sloppy.
Drill out the pilot holes with a larger (M6) bit.
Hand file to a squared-off rectangle slot. Not quite finished in the last pic at right.
File the face of the strip on both sides to debur it after all that filing.
When done, bolt it on. If I had this to do over again I would add another half inch of play fore and aft just to be sure I achieved my goal here.
Yes, of course I replaced that rusty old bolt after this test fit.
The Inexpensive, Custom Frame Bag
Custom frame bags cost a small fortune. Mine cost me $40 delivered to my doorstep. I use a vendor on EBay named Uraltour. Four bags purchased from that vendor so far and all are sturdy, heavy cordura with perfect fit around existing frame bosses and whatnot. You can specify width and since I am buying bags that will hold 18650 battery packs, I insist on a 10cm width. Maybe you can get away with 9cm. Don’t use the default of 6cm unless you have different needs. He will also work with you for shapes other than triangles.
See the little red whatsit up front? Thats my charge cable with a waterproof cover. Ask for flaps top front and rear for cables.
The downside? Well, his business name provides a clue: He’s deep in the middle of Russia. So mailing stuff from Russia to the USA can take at least a month and possibly two. My first bag took three. But thats life. A USA supplier would have provided me with excellent bags, at a much higher price point. Oftentimes they are booked up and you’ll wait months assuming they will take the order at all. Not being able to get a US vendor able to take my order was what made me go looking for another source and finding this vendor.
The Shelf
The space just behind the top tube on the Surly Big Fat Dummy – just ahead of the rear rack supports – is wasted space. A few owners have had custom bags made for this area. I more or less built my own cargo shelf out of odds and ends.
A small bit of aluminum flat bar stock roughly 4″x16″ (I forget the exact size… I had it in my garage from a previous project where I was making a rack floor for another bike).
Another small bit of flat bar stock, about 4″ wide and 10″ long
Leftover 3/4″ ID Silicone hose
Some leftover Great Big Bag closed cell padding
An M6 bolt, washers, a nut, an unthreaded spacer, four zip ties and some Gorilla tape.
Showing pictures of the thing make it pretty easy to figure out how I used the above parts.
The silicone tubing is used to pad the frame. Just slit it down the middle and fit it over the frame tubes. It’ll hold and stay on its own.
Look under the bolt on the crossbar. There’s a spacer with washers underneath so the bolt doesn’t just bend the floor plate up towards the frame.
The padding covers the big floor plate, and the gorilla tape covers that to make a big padded shelf base.
The smaller flat bar plate and zip ties make for a backstop for the shelf. Its sitting at an angle and the last thing you need is for your stuff to slide into the wheel well. I painted mine black but gorilla tape could be used on it as well. Drill 4 holes for the zip ties.
If you look over at the post on A Proper(e)Bike ToolKit – which spells out the BFD’s tool kit – the cheapie MOLLE bag I use there is sold in a pack of two. This is where I use the other one.
This is how I carry along my super duper Pragmasis hardened steel noose chain and U lock.
I keep the keys in the bag with the lock so I never forget them.
The SRAM brakes that come stock on the Surly Big Fat Dummy are good, but on a bike that can take on extreme loads and terrain, they need to be great. I literally use the same brakes on all my bikes.
Magura MT5e 4-piston brakes. The ‘e’ means they have a built in cutoff cable that I can plug into my BBSHD or hub motor.
203mm Tektro Type 16 rotors front AND rear. These are downhill rotors that are 2.2mm thick. Magura brakes are meant to work with 2.0mm thick rotors (typical quality rotors are 1.8mm thick). The Magura calipers will work with the Tektros albeit only barely with fresh pads. Often when I set up a new bike, I swap in partially worn pads from one of my other bikes and give that other bike new pads. By the time the new bike wears thru these swapped-in partially worn pads, the rotors have enough wear that they can take new Magura pads no problem.
Magura MT7 4-piece pads. I still use the 2-piece MT5 pads that come with the brakeset, but as soon as they wear out, I switch to the MT7 pads, which fit perfectly. They have the performance advantage of delivering significantly more measured torque according to reviews. They also can be taken out with your fingertips without removing the caliper from its mount. MT5 pads on the other hand come out from the bottom and to do that you have to dismount the caliper. So better performance and easier maintenance.
The Big Battery
Fopr most of the life of this bike I have been using a 52v, 17.5ah battery pack I bought in 2017 from Luna Cycle. This pack has a 50a continuous BMS and uses 25R cells. The pack has been in use on three successive bikes over the years and has seen almost daily use, with two charge cycles per day since I charge at the office and at home. However, thanks to my ridiculously rigid adherence to best practices when it comes to battery charging, that pack has almost miraculously lost no measurable amount of its original capacity.
However, a bike this size eats power. Especially the way I ride. Recently I purchased a 21ah pack from this vendor and have been very pleased with it. It only barely fits in the Size Medium frame triangle, but it does fit.
The End?
For the Surly? Hell no its the One Bike To Rule Them All. Really, its a great bike and I intend to ride the wheels off of it.
Is it the end of the mods to this bike? Pretty much I think, with the exception of the summer wheels I’m making up using the MYOBDs and a pair of Apache Fattyslick fat tires, for that Kojak street commuter look. Since its a true slick, we’re talking summer wheels for sure. But maybe not as I live in California and like the old song says, it never rains here.
A whole page on a kickstand? For a bicycle? If you are riding a 100 lb freight train whose weight can quadruple when loaded up, there’s more to ponder over than you might expect.
The Surly Big Fat Dummy is a fantastic bike, with one widely acknowledged weakness: The kickstand.
There are those out there – possibly this includes the staff at Surly – who say this is a feature and not a bug. The BFD after all was created as a bikepacking, overland trailblazer. You don’t need no steenking kickstand since you can just lean the bike up against a cliff face, or an axe handle.
Begrudgingly it seems, the Big Fat Dummy is delivered with a kickstand that on any normal bike would be pretty sturdy. Alas on this monstrosity, it is adequate only when the bike is empty, and woefully inadequate when loaded.
How do I know this? Well, ask around any user group, but insofar as personal experience goes: On my first shopping trip with my new freight train, I went to Costco and loaded up four packs of soft drink cans. Since this was Costco, each of those four packs holds 36 cans. Thanks to a total lack of planning and intelligence on my part, I created a load where just the soft drink cans weighed over 100 lbs.
Memo to Me: When shopping on a bicycle, pay attention to how heavy the cart is before you leave the checkout line.
So, my wideloaders were sturdy enough to handle this. My great big panniers were more than big enough. But… how am I planning on loading the bike, then loading the (14 lb, 2-meter) chain and u-lock, and only then climbing on the bike and rumbling across and out of the parking lot? During this loading process, I learned first-hand how important a solid stand was. The next 15 minutes after this picture was taken were a big adventure.
Figure 1: All quiet at the bike rack… things are about to go horribly wrong.
Moving Forward
So, the problem is obvious: If you are using the BFD as a cargo bike and not a bikepacking bike, the kickstand is way out of its league. Has to be replaced. Period. Talking to folks on the various Surly user groups, the Rolling Jackass with its roughly $400 price tag is the best commercially-available solution.
Its DIY Time
I wasn’t ready to fork out that kind of money. I was bound and determined to build my own stand, and I had an idea. How tough could it be?
If you have seen my article on the wideloaders for the Surly Big Fat Dummy, you may have noticed (and seen mention of it in the post) there were some oddball fittings pictured that served no purpose in the published design. That is because I planned an integrated kickstand as part of that project.
The idea went thru a number of iterations. I started with the idea of using simple ‘pegs’: a 3-way elbow on the outside edge, with a length of tubing extending to the ground and terminating in a rubber crutch pad. Place it maybe in the front, or perhaps the rear. Perhaps one on each side, or maybe the front and rear of just one side… what about front on one side and rear on the other?
After mulling the possibilities, I came to the conclusion that every type of peg idea was fatally flawed. There was just too much potential for the bike to fall over while attaching the pegs, or removing them. Especially loaded.
I ended up settling on this: use a 4-way elbow joint on the inner, forward tube joints. Form the actual stand from two pegs attached to one another by another tube to make a ‘U’. And furthermore, make the ‘U’ stand up on its own with another 4-way tee sprouting two short arms that become stabilizing props. This will let the stand be placed in position without someone holding it while the bike is set up onto it.
Its a whole lot easier just to show a picture of the final product than it is to describe in words:
Figure 2: Crossbar with standy-up crossbrace thing completed
The whole idea of making it self-standing was a happy accident sprouting from my need to turn two leftover short pieces of pipe into a full-length crossbar. the 4-way tee was a leftover itself, that I thought I was temporarily pressing into service. I didn’t think to add tubing and feet to the two unused, open holes until I glanced over at more leftover parts lying on the floor. Adding this self-standing (and load distribution) feature turned out to be crucial once I actually tried to use the stand.
Figure 3: This picture was actually taken before Figure 2, during initial construction/guesswork.
And this is what ended up working. I measured the vertical tubes so they only raised the bike up by a bit off the ground. This was crucial as attachment was achieved by lifting the front of the bike up and simply plunking it down on the stand. This is the part where inadvertently making the stand able to sit upright turned out to be (very) useful.
Attaching the stand is easier to do than it sounds. Load on the bike is on the back wheel. Lifting the front is not very difficult even when the back is loaded. And keeping the rise low on the stand is important because it means you don’t have to lift up the front too high.
Removal is also simple. Lift the bike up and the stand falls away (sizing is crucial for this to happen so the stand doesn’t hang up inside the fittings). Push the bike back an inch and set it back down. Grab the stand and toss it into your panniers.
It Works! more or less…
Success! And I still had $400 in my pocket, but… really… after using it for about a month every day, I found the attach/detach process was kind of a pain. As an exercise in problem solving… as a fun project… it was great. But as an expected convenience used with a daily driver. No bueno. And if you have wondered to yourself if, while lifting that bike onto, or off of, the stand it might just fall sideways… I had a few close calls but it never happened, even with a full grocery load.
Still, if your use of the bike is more occasional, this could be a viable option to add into your wideloader project.
Or skip the wideloaders, do a short front crossbar only, use simple single elbows for the stand pegs and work out how to flip it up and down… You could make just a stand with a little more effort and some smarts.
Figure 4: Kickstand/workstand in use
I ended up relegating the kickstand to a portable work stand, and bought the Rolling Jackass (they can both fit). In Figure 4 above I am at a city park, with the bike up on the ‘work stand’ so I can clean and lube the chain. The work stand does a better job than the Rolling Jackass because the latter can come undone if you mistakenly push the bike forward. Not possible with the fixed stand. I like doing basic maintenance at a park after a ride so the time and effort to make this stand was not time wasted.
A short Afterword on the stand…
I made one more improvement – sort of – that might be more successful for someone more determined than I was to see it through. There was a second issue beyond just lifting up the bike and putting it down onto the stand. That lift was actually fairly easy. The real potential for annoyance was if the stand shifted a hair, or my aim was off by a smidge, and the bike hangs up and sits atop one of the open tubes of the stand, rather than sliding into the fitting. Solution to that was to walk over and give it a little kick which, 9 times out of 10, would work. Sometimes not if my aim was really bad, though, and I would have to retry the process. Like I said: an annoyance.
The boat rail fitting itself has an internal chamfer to make fitment easier. And there is quite a bit of extra material there to allow you to hog it out further to make a much bigger well. That would work great. But these are steel fittings about 3mm thick. My poor little Dremel’s grinding wheels just polished that steel and little else. Something bigger and badder was needed and I wasn’t up to it at the time (the job needs a drill and a big internal chamfer bit).
Instead, I rounded off the ends cheap and easy with 7/8″ round end caps. this worked perfectly, but the caps are so tall they make the stand a bit wobbly, since so much less of the pipe is now in the socket.
Pop this onto the tube end. Problem solved.
Whats Next?
So, we went round and round with the kickstand and in the end, bought one and use the other for a work stand. Fine. I’m not done yet as there is one more goofball problem to solve.
Where I work, I am lucky to have my own private garage where I can park the bike, hook up a charger, turn on a couple of industrial fans to blow the sweat off me and change into proper work clothes. I’ve even got a small air compressor, a big rug and a nice padded chair.
There’s only one problem… to get into that garage I have to make a U turn through a narrow walkway under some stairs.
Figure 5: uh oh…
It was never an issue until I built a bike almost three feet wide and over 8 feet long. Yeah I sort of didn’t really focus on that until after I had the build completed. You’ve probably heard the story about That Guy who bought a pickup and then realized he couldn’t fit it in his garage? What an idiot, right?
Problem Solved!
Use the little dollys that people use to move around pianos and pool tables.
Figure 6: Choose your product carefully. A lot of them have horrible reviews.
Throw one under each leg of the kick stand and just wheel the thing around as you please. Easy peasy.
Figure 7: Hello Dolly! Note the Rolling Jackass, and the still-in-place elbows for the ‘work’ stand.
Moving the bike into the office garage through that narrow entryway is a snap. Without them its still possible but involves a lot of dragging and lifting and fighting and cussing.
Last But Not Least (At Last!)
Take a close look at Figure 7. At the feet of the Rolling Jackass kickstand. Underneath them. Looks like some kind of disc or foot? Well, it is. If you refer back to the Frankenstein boots for the Ursus Jumbo, I did essentially the same thing here. The idea was the steel feet of the Rolling Jackass – are thick steel. they will probably last a long time, but I want them to last forever. I also park the bike in places where I do not want the floor scratched (like the marble floor of my bank’s lobby. Yes really).
Using the same process I described in my other post on the Jumbo, I layered on about 10-12mm of Shoe Goo… the artificial shoe-leather. It became a flexible but durable sole to the Jackass’ steel shoes. Before applying the Goo, I roughed up the smooth steel surface of the feet with some power tools.
10-12mm may seem thick, but that thickness is necessary to keep the edges of the steel feet from digging into the ground as you lever the stand into the down position.
The security guard at your bank will thank you for taking the time to go that extra mile.
The Surly Big Fat Dummy has a great big deck in the back. Using a 40″ kicktail longboard and some hardware, Lets make it bigger. And a double decker to boot.
Back when I put together the Mongoose Envoy Project, I used a skateboard deck to cover over the long, but only marginally-useful-on-its-own rear framework to create what ended up being an aircraft carrier landing deck.
I started out with a 33″x10″ double kicktail which I mounted on top of eight 25mm tall by 13mm dia. spacer posts. The idea behind the spacers was to give me some working room to attach a net to the top of the deck, and have room to easily mount its hooks to those posts. It worked well, but I left money on the table with only a 33″ deck. I could go longer. So I did. I found a 40″ longboard with a single kick and mounted it on 10 posts, this time.
It was great, but of course, I thought I could go one better. So I scored a 44″ double-kick longboard, and – since the 25mm posts were a bit fiddly trying to get my fingers in that small space – swapped out for taller 40mm replacements. I also made some other improvements, and that deck remains on that bike as you see it here to this day.
Fast Forward To The Present…
Now I have a Surly Big Fat Dummy, and I want to do the deck idea one better (AGAIN!). I still have the 40″ deck left over from the Mongoose build. Since the BFD is already like 8 feet long I don’t need something that makes it longer, so this ‘shorter’ deck will do just fine. I drilled some new holes, repainted it and took the spacers a step further.
The Next Level (literally)
Unlike the Mongoose, which had nothing but a framework, the Surly Big Fat Dummy already has a pretty good deck as it is. On the Mongoose Envoy I was trying to cover over the bare framework and make something useful. This time I am trying to make something already useful more so.
To preserve the utility of the existing deck, I went with much larger spacers. That created a ‘hangar’ under the deck of this aircraft carrier of a bike. This new hangar’s purpose is to house things that need to be carried along, but generally kept out of sight. Stuff where I can benefit from it being reasonably handy, but kept out of the way.
Great Idea. But first I had to assemble the parts and make the thing.
Airframe bolts have a specific thread length designed to fit a single bolt and a single double-thick washer. This project uses 4 washers of two different varying thicknesses. Measure carefully.
Wow thats a lot of hardware
Like my previous decks, I wanted to use enough spacers and bolt anchor points to make the deck an integral, structural part of the frame. No wiggling possible. Part of what it takes to do that is to use the widest spacers I can find (the 5/8″ OD are it, and dictated why I couldn’t stay metric). To further solidify the connection laterally, I needed washers everywhere clamping everything.
You can still see the holes from when the deck was bolted to the Mongoose, as well as the holes for the trucks that aren’t there anymore.
And excepting the spacers themselves, its all Grade 8 hardened steel. Its. Not. Moving.
Notice also I used hex bolts and did not bother to work with countersunk heads, matching washers etc. as with the previous decks. This thing is spray painted in truck bedliner to help keep things from sliding around, and the hex bolt edges do the same job.
Airframe bolts exist in a wide variety of very finely diced sizes. I am not giving the size I used because the ones you may need will vary according to the thickness of your top deck.
Here’s what the finished assembly looks like up close:
Now that the aircraft carrier has a landing deck, we find out what we stuff down underneath in the hanger.
Up front, fitting just barely between the front posts, is a 3-amp weatherproof adjustable charger that is a permanent companion to this ebike. In the middle is the toolkit for this bike, containing a pump and all sorts of other goodies. It fits just between the two sets of spacers so it can be dragged out the side. And in the back we see a big thick plastic ziploc freezer bag wedged in between the rear 4 stanchions. Thats the in-case-of-disaster emergency inner tube.
Since then I have added another little jewel:
Thats right. A folding chair. Held rattle free thanks to the net. Stuck in line at curbside pickup? Have a seat and relax.
Take the crap off the top of the deck and you have yourself a work table. Or a coffee table. Or a picnic table. Its 40″ long so use your imagination.
See that net? Its 30″ long before it gets stretched out, and since I ordinarily have the Great Big Bags on the bike, I generally do not need to use the top deck for storage of items up so high. But when I do, that nice long cargo net does a great job.
Here is one of the rare times the bags are full and I need to stack something up on the deck other than a rolled up jacket
Now What?
Got a Big Fat Dummy? And a drill? And a skateboard? Make yourself one of these. Next time you have to sign a peace treaty, host a banquet or make off with an emergency supply of toilet paper… you got this!
WARNING. Before you start fooling with your BBSHD settings, take a photo of each screen with your cell phone. If you screw up, you have a quick reference back to your original settings.
The subject of what settings to use when programming a BBSHD comes up now and again. Its a question with a fairly complicated answer that does not lend itself to your typical Facebook 2-sentence post. So here is the long version. I have my own suite of settings that suit my personal riding style. I am primarily a pedal-pusher: I want to get exercise when I ride, so I seldom use the throttle. But if you try to take that throttle away, you’ll have to pry it from my cold, dead thumb.
Keeps me working, but not too hard … unless thats what I want, and then it has to let me do that, too.
Interestingly, with both my Mongoose Envoy Project and Surly Big Fat Dummy Project, I found what worked great for me on other BBSHD-equipped bikes was completely ineffective on a cargo bike. I frankly haven’t figured out why this is, but I think it may be because my older builds were just that: Older. Something maybe changed in the firmware. My PAS settings that conserved major amounts of power while pedaling wound up being totally inadequate. I needed to step up some settings, which I will describe below. While my settings then vs. now are quite different, I don’t see any real penalty in range.
Feel free to tinker using both and see for yourself what happens to your own motor.
How do you program a BBSHD?
Strictly speaking, you don’t. As a for-reals programmer who for most of his life made his living writing code, I have to point out this is not programming even if everyone calls it that. The BBSxx line of motors have a quasi-hidden settings interface. With the right software you can gain access to those settings and simply change them, resulting in big differences in behavior.
Myself, I am using the Black Box sold by Luna Cycles (available here). The Black Box makes it much easier to go on a ride, tweak as you go and get things just right after only one or two rides. Also, I literally have a half-dozen bikes now with one of these motors. The initial expense of the tool is a lot easier to justify if you are sharing it across the Pacific Fleet.
The other way to do this is to spend about US$18 and buy a laptop cable. Then you use your existing Windows laptop to host the app that you will use to make the aforementioned changes. Here is one place to get that Windows app. I started out doing it this way, but as laptop operating systems evolved I found it increasingly difficult to get Windows to accept the cable’s right to exist. I don’t miss fighting with it one bit.
If there is such a thing as a bible on how to program your BBSHD, its Karl Gesslein’s blog post on the subject (read it here).
If you want to know everything about programming your motor, you should read the blog post linked above. That post is the definitive tutorial on the interwebs, despite its age. All I am doing here is calling out some of the things I have done that deviate from the norm, work for me and why it seems that is. So I will not be explaining things as if you have never seen any of the BBSHD settings screens before. This article assumes you have at least read the above blog post and familiarized yourself with the screens and settings.
I am not showing original factory settings. Your motor may have settings your vendor considers proprietary. So I am showing screens I have altered and then calling out the bits I consider important.
The BBSHD’s settings are presented on three separate screens: Basic, Pedal Assist and Throttle.
The Pedal Assist Screen (2 of 3)
Yes I know. I’m starting out of order. Its easier to understand this way.
Much of what is on this screen… you shouldn’t mess with. I’ll just hit the high points.
Regardless of what you see here on my own screen, I strongly suggest you leave the first three settings alone unless you know exactly what you are doing.
The Pedal Assist screen on 2Fat – my ti-framed 2wd bike whose motor dates back to about 2016. I use these settings on new motors as well.
Start Current
The lower you set this number, the more gentle it is on the controller and your drivetrain. Experimenting with lower numbers will make life easier on your rear freewheel pawls, and chain. Setting this number low is especially helpful if you are running a cargo bike under load and want to be extra careful. Setting this to lower numbers may also be too little startup assist – remember the purpose of the motor is to help you get off from a standing start. This setting only applies to pedal-assist power delivery.
A typical default number here is higher; often around 10. I have found kicking it down just a bit more is much better for your drivetrain if you have a heavy (cargo) bike; especially one that is loaded. Even if its not a cargo bike, how bad can it be to beat on your drivetrain less? Remember you can always mash the throttle if you want <clarkson> power </clarkson>.
Slow Start Mode
This setting determines how gentle the ramp-up is on your power on start. Starting up too fast can kill your motor’s controller so beware. I am using the lowest setting published in the article I linked above. Here again, why create a situation where you could end up blowing your controller or chewing up your chainrings? I stay on the conservative side.
Stop Delay
A common complaint on the BBSxx motors is that you can stop pedaling and the motor keeps going for what feels like a full second. Its a valid concern. 5 is the lowest safe number for the BBSHD so thats where mine is. This setting effectively means your motor stops when you stop pedaling.
BUT it also leaves a hair of rotation which you can use to your advantage when shifting gears: Stop pedaling and in that instant execute your shift. The shadow of remaining power and rotation will be enough to gently complete the shift (SRAM gears will shift in about 1/4 rotation) and you can start pedaling again almost instantly. I call this a ‘stutter step’ in my cadence and I personally prefer it to using a Gear Sensor which automates the process. Tomato-tomahto. Depends on how you learned to use the drive as to which you like better.
Current Decay
This is a big one. Current decay helps decide when your motor cuts power based on your cadence. A huge complaint about cadence sensing is it causes the bike to run away from you and the rider is just spinning the cranks… its called ‘ghost pedaling’. This is part of a complete solution to that problem.
My philosophy is (and plenty of people disagree with this) if I can pedal at a high cadence I don’t need power assist, since I can spin the cranks. By cutting the power back when I start spinning (a.k.a. “clown pedaling”), I not only reduce power consumption and increase range, I also create a scenario where I either keep going on increased amounts of muscle power (which a high cadence demonstrates I can pull off), or I decide to shift to a higher gear, thereby naturally slowing my cadence and telling the motor to give me back some power.
This in turn has the effect of letting me ramp my cadence back up and increase my speed. Done right, this is much closer to a natural cycling experience and either lets me a) haul ass to my destination on the streets or b) get a hard workout. Or both.
Why would anyone disagree on this point? Easy: If you are running a powered bike on singletrack, and you hit a steep hill that is all muddy and root-strewn, you need to spin to keep yourself going up that hill. If the bike gently ramps back power on you, well thats a dirty trick indeed. So… remember what I am describing here is maybe the magic elixir for street riding; but not for an eMTB running hard singletrack.
Stop Decay
This is another setting that helps govern how fast the motor shuts off when you stop pedaling. Zero milliseconds sounds good to me. Stop Delay determines how fast a motor begins its shutdown after you stop pedaling. Stop Decay determines how fast it fully shuts down after the shutdown begins.
Keep Current
This is another companion to Current Decay. When Current Decay decides to cut back power, this percentage determines how much power you keep. So by setting mine to 40%, I am getting a 60% power cut when I spin my legs past the Current Decay threshold. And my Current Decay setting determines how steep the offramp is down to the lower power level.
Here again remember what a bad idea this can be on an eMTB. This is for city riding and commuting, where you want the benefits of boost but you also want the option of getting some exercise and your terrain is reasonably predictable.
The Basic Screen (1 of 3)
The BBSHD is capable of supporting up to 9 assist levels. Actually its 10 since there is a Level 0, but that level is (nowadays) a special case that you pretty much have to leave at a special setting and can’t adjust.
Each level is defined with two numbers. A Current % Limit and a Speed % Limit. They are, in a word, opaque in terms of what they do, and not easy to understand.
Also I have achieved great results in entirely different ways on different bikes. I’m going to show multiple screens.
This is my ‘old school’ screen. It works as a power-sipper on older BBSHD motors. I can not use this on motors I have built bikes with in maybe the last 2 years.
Note the Level 0 setting of ‘4’ with a speed cutoff of 30%. The intent there was I never really want zero power on pedal-assist and Level 0 provided a very mild bump for times when I am pedaling slowly and going slow… like when on an oceanside bike path loaded with tourist pedestrians, and I am just barely exceeding walking speed.
Here’s the ‘modern’ motor, pedal-assist-friendly version. Note the 25a power reduction (and ignore it).
This one is apportioning quite a bit of additional power, level by level. On the newer motors, this is what it takes. The 25a power reduction shown on this screen is specific to this bike and not something you should read anything into. Just know that the Current box is where you limit the amps for regulatory or other reasons (i.e. this is your maniac child’s bike).
Whats with the Assist 0 setting of 1 and 1 above? Its a requirement of newer BBSHD motors. If you set it to anything besides 1 and 1, you wind up disabling pedal assist. This is far from my preferred setting as you can see above. I originally used Assist 0 for sort of a crawl mode when wending my way through tourist-laden sidewalks, where I’m going just a bit faster than a walk and don’t want to run anyone over, but still want a touch of power. Bafang’s release firmware is a moving target so if this changes I’ll amend this note.
Current % is when the power cutsout based on road speed.
Speed % is when the power cuts out based on motor rpms
Whats this ‘cut out’ stuff? Well, remember the ‘decay’ and ‘keep’ stuff we described when going over in the previous screen? These settings help determine when that kicks in. Clear as mud? You’re not alone. ‘Counterintuitive’ is the name of the game when messing with your Bafang motor settings.
Screen 3 of 3: Throttle
So… the pedal assist levels are on the Basic page. Makes perfect sense. Strangely, the throttle settings are on the Throttle screen.
There are only two things that, really, you should be fooling with here.
End Voltage
Generally this stops at ’35’ or 3.5v. What that gives you is, effectively, a throttle that has two speeds: Completely Off and Full Blast. Not really but it will feel like it.
Instead, if you set End Voltage to ’42’ (4.2v) the result will be a smooth, linear throttle where it will be easy to, say, blip out only 200w of throttle-based assist to your motor while you are struggling to get going after a stop. Being able to dribble out just a bit of power is something your cassette pawls – and your wallet – will appreciate after a few thousand applications. No more clanging noises coming from your poor, soon-to-die rear hub.
Start Current
Hey waitaminute… we had Start Current on another screen too! Yes we did. But that one was Start Current for pedal assist. This one is Start Current for when you mash the throttle.
If you set this to, say, 10%, that means the initial beat-down given to your cassette body by the cluster (that gets jerked forward by the equally unhappy chain) is only 10% max the power of the motor. The rest of the power you asked for gets poured on a split second after that. But the initial shock to the system is reduced by this setting, which has obvious benefits. For a heavily loaded bike where you want a smooth startup on throttle, setting this down to 5 (or less!) should be considered.
Wrapping it all up…
So there you have it. This is FAR from a comprehensive tutorial on the subject. Remember also that everything done here is done for a BBSHD that is running a 14S/52v power system, so if you are, lets say, running 48v… its possible you may want to jigger some of the assist levels a bit upwards. But now you can do it with a starting point.
Last Note:
The settings above are my personal settings. Starting from a stop, my assist will not kick in until crossing 5 mph or roughly 8km/h. If I want assist from a standing stop thats what I use the throttle for. Remember: All this pedal assist sturm und drang is wiped away if you just use the throttle and make it go.
