52v, 32ah single battery, skateboard config (box under cargo floor)
KT and Bafang displays
160 Nm rear, 45Nm front
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.
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.
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.
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.
So, my Gen 1, 1.5 and 3 bike layouts are all twin geared hub designs. What was Gen 2?
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.
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.
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.
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.
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?
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.
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.
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.
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.
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.
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.
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).
Here’s where the eagle-eyed may spot a preview of how I ride this bike to soften up the mid drive.
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.
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.
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.
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.
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…
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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?
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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