Larry vs. Harry Bullitt – the Battery (Box)

A big bike with two motors needs a big battery. Lets take advantage of the frontloader design to hide the battery.

A big issue with an ebike – particularly one that is left outside on its own all the time – is battery security. The battery is maybe the most expensive component on an ebike and its a big theft target. So typically you have to carry the thing inside with you, and hey… thats a real pain in the neck. Not only is it a really heavy black brick, but you have to dismount it and re-mount it to the bike, and disconnect and reconnect it to the motor (forget about your display keeping the correct time and date), every single time. I have come up with my own way to make the best of this bad situation for my other cargo bikes, but with the Bullitt, we can make the problem go away.

The Kinda-Secret Compartment

Take a look at the picture above. See the big black box under the cargo area, near the ground? Thats it: the battery box. You’d be surprised by how many people don’t notice it. Even if they do, what are they going to do about it?

I had seen a few other Bullitt builds with battery boxes and they seemed like great ideas: The battery goes out of sight, out of mind under the floor of the bike. It lets you get creative on battery size (as in you can go bigger if you like since there’s lots of room down there). It may even be made secure enough that you can just leave it on the bike – eliminating maybe the biggest inconvenience of using an ebike for daily errands and shopping.

Also, just as with electric auto designs, a ‘skateboard’ config for the battery puts it centered and below the floor – down as low as it can go. That is as good as it can get for performance.

But I was thinking of none of these things when I was putting together my build sheet. I was still thinking I would do another quick-carry sling pack with the battery inside, and toss that pack into the cargo bay for easy removal and replacement. It wouldn’t be secured to anything but I would see about figuring that out later on.

My sling pack with a 20ah battery inside, used on my Surly Big Fat Dummy

But while the parts were still trickling in, I was participating in a discussion on the Bullitt Universal Owners Group on Facebook. Another Bullitt owner showed off his own build and mentioned his battery box – and that he had gotten it from Splendid Cycles – the same shop where I got my Bullitt frame and parts. I gave them a call and in short order one of the last examples they had on hand was on its way to me. I was told up front the box was a blank canvas, and I would need my own elbow grease to add mounting holes and any other refinements, such as waterproofing, cable exits etc.

As-delivered, the battery box looked as you see it below. A simple slot holds it up on the back. Its front at first seems unnecessarily complicated, but is quite clever. Its seamless, unbroken face prevents any direct channel for water ingress from the front, just behind the tire. The cutouts necessary to let the box slide into place doubled as my exit points for the power, charging and temperature sensor cables, so no need to cut any holes. It fits absolutely flush to the near side of the frame so no insulation is needed or wanted. Its shape is angled on one side to clear the steering tube.

The box as-delivered, almost. I used black flexible silicone sealant to all the internal seams, and dabbed over all of the rivets as well.

Box Installation

The first step was to drill the box so it could be fixed in place. As-designed, it would stay put. But I am sure there would be some shifting and rattling… and I can’t abide rattles. Also, the existence of the box complicated the installation of the honeycomb floorboard. The floorboard expects to be able to drop a bolt straight down and use a nut underneath to lock it down. Well, now that bolt hole is completely inside the box on the front left corner. Its outside on the right front, but not by much. I needed to change those two mounts to fixed studs going from the bottom up.

I also wanted to add an entirely separate bolt on the front dedicated to strongly fixing the box in place. I decided to use an oversized hole, and used a hand file to enlarge it to a rectangle. Following that, a combination of an oversized, hardened washer and a flush-fit M8 bolt gives a flat fit that works under the honeycomb board fitting directly down on top of it.

The new ‘studs’ are common, long M6 socket caps with – get this – a Presta valve nut to hold them in place. I needed a low profile nut and there’s nothing lower-profile than the common presta nut, which even fits snugly inside the bolt hole manufactured into the LvH honeycomb board.

Forward box mounting complete. Two studs are ready for the honeycomb board, and the center bolt holds the box tight to the frame.

For the rear of the box, to match up with the honeycomb board’s rear mounting hole, I had to use another M6 rather than go with another big M8. I drilled a thin hole thru the box’s top flap and the honeycomb board’s rear mounting bolt goes thru there. However to be consistent – because I wanted to use security nuts to make getting into the box that much more difficult – I made it go in from the bottom-up like the others (we’ll show those security nuts etc. in more detail when we talk about the cargo box installation).

Now Install The Battery

At this point, the next step in the installation process – which, maddeningly, has to be done in this order whether you like it or not – was to install the battery.

You can see how I accomplished that below. All of the padding is closed-cell, and I left as much of the battery untouched by foam as I could. The battery lays on the bare alloy of the box with no padding (a solid metal wall is plenty of protection). It is surrounded on four sides such that it cannot move, even after months of pothole pounding commutes and store visits. I disassembled the bike after 500 miles and looked inside to be sure of this. No water had gotten in either despite riding in rainstorms.

There is a brake cable braze-on above the pack underneath the center bar. It is perfectly positioned to smash into the cells underneath if the pack bounces up to meet it. I prevented this possibility via some left over Minicel T600 EVA foam (you’ll see what I used it for in the Cargo Box episode) to fix the battery in position (i.e. keep it from bouncing). Two pieces are used, one on each side of the braze-on. Underneath this area the visible green rectangle is a piece of thin metal fence strapping which provides a last but certain line of defense against that braze-on ever contacting the bare pack.

The battery is literally incapable of movement on any axis. It is held solidly – but not enough to smoosh anything. Rapping on the box with your knuckles yields a satisfying thunk as if you are rapping on a solid block of metal.

Lets Talk About The Battery

An AWD bike needs a lot of power. Even one where I have toned down the power to civilized levels. You must have a pack whose Battery Management System is strong enough to run two motors at once, and if you get into the subject and learn the specifics, you will find out real fast that commercially-manufactured battery packs can’t cut the mustard (this is why commercial AWD bikes have two separate batteries). If you want to build the bike right as opposed to building it cheap and sucky, you have to get yourself a custom pack built that is tailored to the job.

Pack Details

The battery itself was built custom to my specs after some discussion with Matt Bzura at Bicycle Motorworks. This is one of several packs I have purchased from his firm, after hearing nothing but good things about his work from other builders over the span of a few years. I’ve had nothing but good experience working with him as well.

I knew that an AWD bike needs more power, so the battery pack needs to be bigger than usual. And the Splendid Cycles battery box is a big sucker. If I put in a battery that filled that box it would be TOO big. Looking at the box dimensions and knowing what I wanted to do for crash padding gave me one half of the picture. Matt @ BicycleMotorworks filled in the blanks with the dimensional details of the cells and battery management system chosen for the job.

Cells Samsung 40T (21700’s)
Pack Config 14S8P (52v)
BMS Capacity 70a Continuous output
Amp Hours32
Output CableXT90S / 8ga
Charge CableXT60 / 12 ga

The 40T cells in the larger 21700 size, and overall pack design allows it to operate under load without voltage sag, and without heating up, despite the enclosed space and the dense, closed cell padding that holds the pack fast. A temperature sensor is attached to the pack top and runs outside of the box for easy visibility from the saddle.

What About Heat? 
In use in a normal climate - bearing in mind its sealed in a big metal box - the pack does not get noticeably warm over and above ambient air temperature - nothing over 5 degrees Fahrenheit above ambient.  However, 5 degrees over ambient is a lot when its 105 in the shade, where in the sun, the pavement is radiating heat at 130.   In severe heat (as I write this, the end of next week is scheduled to reach 114°F, which is more than 45°C) I need to plan ahead for where the bike is going to be parked, and plan my route to provide the shortest, shadiest path to my destination.  Our local area has already experienced several days where the temperature has exceeded 110°F / 43°C. Even though the battery cells are not thermally coupled to the case, I ringed the box with heat sinks to help keep the pack a bit closer to ambient temperature.  They have reduced pack surface temperature by up to 5 degrees. 

The battery charge cable is routed outside of the box along with the power cables, and comes up as shown in the photo below (the green plug). This plug is semi-rigid thanks to the manner in which I insulated the end connector, as well as how its braced against other secured wiring. It is easy to access, protected from the elements via the plug cap and not going anywhere. In winter months a rubber band and some plastic will ensure nothing can get through and cause any fireworks.

And last but not least… this is a 52v battery that has a capacity of 32 amp hours. I like having batteries big enough that range anxiety doesn’t exist. You simply go ride the bike and do what you need to do. Considering the bike – thanks to its motor configs – eats only 400-500w at cruise… my ass will wear out in the seat before the battery charge does…

So long as I remember to charge it. But even then – and this has happened to me already – the battery is big enough to maybe rescue me from that faux pas.

The battery temp sensor sits here, without any need for actual mounting. The Bullitt’s ride is so stable nothing more is required. The charger plug is covered in a green cap at center.

(not) The End

Thats about all I have on the battery and battery box. We’ll stick to the same area of the bike in the next article in the series, as the two of them are linked together:

The Cargo Box {live link coming soon}

The Bullitt, by Larry vs. Harry – Cargo Bike Build

And now for something completely different. The Bullitt from Larry vs. Harry is a bucket list bike that (now that its finally done) I love to ride. This series will cover the details of a frame-up build that includes AWD electrification.

Originally, this was going to be a single article that covered everything. However, as time progressed and I got more and more of the details written down, I found I was at almost 6800 words, and could easily hit 8-10,000 before completion. Thats too damn big, so it had to be broken up. This opening post will cover some of the introductory bits. Then we’ll split off into followups that hit the high points of the various things worth bringing up.

There’s a lot to get to so lets jump in.

Background

Having built up the Mongoose Envoy as my first cargo bike, then supersizing to the Surly Big Fat Dummy, you would think the Larry vs. Harry Bullitt was my third choice for a cargo bike. It was the opposite: The Bullitt was my first choice. But first,

What the hell is a Bullitt?

A Bullitt is a bakfiets. How does me saying that help you? It doesn’t, until I add that bakfiets is a Dutch term that means “box bike”. You’ll be helped along a bit more by the fact that a bakfiets is often referred to in English as a ‘frontloader’. So, the box is in front of the rider. Here is a Google image search that will let you see a slew of them, of all different types.

Looking at all those different pictures, they all look sort of like 2- or 3-wheeled dump trucks. Not exactly a fun ride. But thats to be expected of freight haulers, right?

So, What the hell is a Bullitt?

A Bullitt is a frontloader-style cargo bike made by Larry vs. Harry in Copenhagen, Denmark. It does its cargo carrying job, but its also specifically designed to be nimble, on a frame that is relatively rigid. Its also meant to be those things in a lightweight package, where that frame is lightweight alloy (whose inherent rigidity is mitigated by the sheer length of the frame. A Bullitt is also a very comfortable bike to ride).

In short, the Bullitt is a cargo bike for people who still want to have fun riding their bike. You aren’t schlepping around in the bicycle equivalent of a minivan.

This gets the idea across in 1 minute.

When I originally decided to build up a Bullitt, I set up my build sheet and began listing out components. But before I finished, the cost crossed my pain threshold and I chickened out. This was going to be my first cargo bike. I had no experience with the platform, and wasn’t even sure I would like the idea, never mind throwing in the funkiness of a frontloader. I wasn’t ready to make such a big financial commitment.

So I went the budget route with the Mongoose Envoy. I used that frame and fork as a donor platform to develop a really nice lower-cost cargo solution. After some use I decided 1)this whole cargo bike thing was really cool and 2)the Envoy wasn’t big enough for the XXL jobs I wanted to give it.

When I was doing my research prior to buying the Envoy, I had almost bought the much larger Surly Big Fat Dummy, but bailed on that one too due to the same kinds of newbie uncertainties that led me to bail on the Bullitt project.

So, wanting to upsize, I went there next. That bike has been a thing of beauty. I loved it and still do for a variety of reasons beyond its utility as a cargo bike (and a bikepacking bike. And a take-the-trails-route-instead commuter. And an unstoppable freight train that terrifies all who cross its path). The Big Fat Dummy truly is a BFD.

But…

Using the BFD for all things, every day, I could see room for improvement. Stuff that bugged me and worse – slowed me down.

At the shops, you have to bring the battery in with you or risk getting it stolen. I had a solution for this but it still takes effort to deal with and is a pain. Additionally it limits the size of the battery as the bigger it is, the more trouble it is to carry around.

The BFD has two panniers that hold more than 275L (not 27.5… Two Hundred and Seventy Five). Who can ask for more? Except bags that big aren’t kept opened up and ready for use. They’re folded up and strapped to the frame. Expanding them requires some fussing and fiddling with the straps. Not the end of the world but it has to be done. And then you need to cinch those four to six straps down to secure the load. And balance your load between the bags or bad things can happen. When you are doing this every day at multiple stops, you start wanting things to be easier… but how?

Enter The Dragon

A Bullitt from Larry vs. Harry. Thats how. A bike purpose-built for a narrow type of use-case: urban utility. The Bullitt is the most nimble and rigidly-framed of the genre: the sports car of the frontloader world. The battery on this bike will be locked in a quasi-concealed, sealed box under the cargo floor of the bike; out of sight from prying eyes and prybars. No more lugging it into the store with me. Most importantly, the bike has a floor in the first place. Cargo is held in a great big open box. I can just walk up, dump my shit in and and take off. No more pre-flight prep.

Also I kind of liked that it looked weird… and I had no idea whether I could ride such a contraption. I don’t get that kind of uncertainty with bikes much these days and I looked forward to the challenge.

Oh, and since LvH decided to call the green paint on the bike Lizzard King, well that makes for an obvious name for the bike.

Bullitts are – wonderfully – built up from frames and customized by a great many of their owners. So even though I am doing a lot of writing-up here, there’s not much point in doing full how-to’s, since thats how most everyone does it already, anyway. So my focus will for the most part be more of a high-level one rather than getting down and into the finer details of Tab A inserting into Slot B etc.

What a mess! A month or so after initial build completion my custom battery arrived… time to take it back apart!

So Lets Build It Already!

So much going on… Where do we start?

The Frame Kit

Your local Larry vs. Harry dealer will happily sell you a complete bike, or even one whose frame has been purpose-built to integrate an electric motor. You can choose an internally geared hub, and the frame has a split in it to allow a belt drive. Lots of options for a complete bike, or buy their frame kit and build your own.

I chose the frame kit route. The kit comes with the frame, fork, steering arm, headsets (plural) installed and a number of other components that are unique to a Bullitt’s construction, so you don’t have to go searching all over creation for weird parts. I also purchased the “honeycomb floor board” (the cargo deck) and the “side panels” (hard sides to the cargo area that turn it into a big bucket). It all arrived in one giant box, too big for UPS so it was a LTL freight carrier in a full sized semi-hauler that brought it in. The truck was so big it had to meet me on the street.

I purchased the frame kit from Splendid Cycles up in Portland, Oregon. I handled the transaction entirely over the phone and the folks at Splendid were both helpful and generous with their time, answering my technical and build questions and making sure I was taken care of. Delivery was prompt and I was frankly amazed at how well the frame was packaged once I got the box opened up. Oddly enough I met the tech who packed my frame online, in the Bullitt Facebook group, who was happy to see I got the frame and confirmed what was visually obvious: he had spent time making sure it was packed well so it would get to me in the same shape it left their shop.

All Wheel Drive

Even though the bike only took me about a month to build so it was at least roadworthy, there was a lot going on with this bike. Most of the reason it was such a pain revolved around this one feature. In the end, it was worth it, but the added complexity of an AWD ebike is not for the faint of heart.

Two-motor AWD means wires everywhere. Hiding them is something of an art form.

I have built several all wheel drive ebikes, but not recently. I decided the Bullitt was going to be the proof-of-concept behind a different, more civilized/everyman form of ebike AWD that I had been mulling over for years but never did anything about. That subject, the merits of an AWD ebike and the specifics surrounding it are all dealt with in a separate case study in my dual-motor AWD ebike series. I’ll let that post and its companions stand on their own and just say that the sort of cooperative, drama-free AWD that was put into the Bullitt is, in my estimation, a tremendous success with regard to making it a viable all-day, everyday auto replacement.

Which leads us straight into the next episode:

The Battery (and Battery Box)

BBSHD Aftermarket Controller Bracketology

Seeding BBSHD aftermarket controllers has gotten more complicated in 2021. The 2021 choices have seen BBSHD market gorilla Luna up their controller game. To take on start up ERT in the F.O.C category, Luna has recently beta tested their Ludi V2 BBSHD controller. Luna explicitly states to “use this controller in off road only situations”.

The gray wire is an antenna for VESC dashboard & upgrades via Bluetooth on Android device.

I installed a Luna Ludi V2 FOC controller on my Specialized Pitch BBSHD conversion that utilizes a 42T Eclipse and wears Schwalbe 27.5 Moto X tires. Prior to upgrading the controller, the Luna 860c display showed a little over 30 hrs of riding time. I ride the same 25mi route of asphalt with this bike. It’s powered by a Luna Dire Wolf 52v 21aH battery that contains  84 LG MJ-1 18650 cells configured 14s6p.

I love this bike! It’s nimble and has crazy long range via 21aH Dire Wolf. It’s even color matched!

My commuter routine is about 12 mi asphalt in AM. Charge at work to 80%. Then ride home same route. Without changing gearing between the stock BBSHD controller loaded with Karl’s Sauce Settings and the Luna Ludi V2 controller, I have gained about 8 mph top end speed and my battery consumption has remain the same or slightly decreased.

The only issue so far with the controller upgrade is that the battery indicator goes red during acceleration or hill climbs when below about 50v. Previously the stock controller with Karl’s settings at the same mph and same gear selection did not trip the battery icon to red on the Luna 860c display .

On average, I am consuming about 3v less of total battery upon arrival at work, which is the 12 mi mark, before charging the battery to 80% using the Luna battery charger. My transit time is about 45 minutes to work and is nearly all ghost pedaling.

I am basically maintaining the same speed covering the same distance arriving at the same time to work but using less battery. This is possible because I am using less wattage/requiring less PAS as observed on the display.

Best 1st build BBSHD platform is a Thud Buster seat post on a mechanical discs hard tail frame.

The efficiencies can not be attributable to becoming a better ebike rider; getting more efficient in gear selection, braking, running stop light etc. If anything, I have greatly decreased gear changes. I am staying in my most effective cassette gear of 24T, 3rd biggest cassette gear, and not downshifting to provide more leg drive. 24T provides maximum chain wrap with out stripping. The previous 25hr of bike time I stripped out the lower tooth gears to the point I can’t use them under BBSHD power or human only power; the chain just skips terrible in those smaller cogs due to not enough chain wrap and the cassette teeth being worn down.

How much did I pay? This was beta and I did pay my own $. This is not available stand alone from Luna right now. If you want the Luna Ludi V2 FOC controller you have to buy a Luna BBSHD bike. In the past I did buy a Luna Ludi V1 controller for over $200 and I did buy an ERT NXT BAC 855 BBSHD kit for over $500. This beta was somewhere in between.

Make double sure you have the phase wire spade connectors seated properly to the BBSHD.

Is the Luna Ludi V2 desirable? YES!!! At the very least you can extend the range of your current battery. You can get more top end out of your bike and using throttle only you can reach a higher mph.

It was very straight forward to install. I have previously removed BBSHD controllers. I am familiar with how the PAS clip and 6 halls/temp clip operate etc. After you get familiar with this, it took under 1 hour to remove the stock BBSHD controller and install the Luna Ludi V2. It took about 10 minutes to silicone/water proof the connections.

Pro Tip!! When connecting the 3 BBSHD phase connection spade connectors, make double sure the spade goes into the female socket …… Plus look at the 4 pin PAS and 6 PIN halls/temp connector on your V2. Hints can be found how to disconnect your stock controller by actuating the retainer clip of the connector. When you disconnect wiring looms do you generally just grab and yank??!! No. Look at what came with the kit and carefully disconnect the stock controller by actuating the retainer tangs!

2nd Pro Tip!! Elevate the bike. Hang your bike by the front wheel and try to get the BBSHD/bottom bracket as close to eye level as possible. I had the luxury of a ceiling hoist. But you can use your garage door track or a ceiling hook as well. This will make it much easier to remove the stock controller and install the upgrade after mkt controller. You have to water proof all connection in the BBSHD before screwing down the controller and this is much easier at eye level.

It’s a tight fit to get everything folded back properly and the controller fastened to the BBSHD.

Luna has posted a firmware update. Using the VESC app, my nephew flashed the controller wirelessly using his Android phone and the blue tooth connection via the small antenna sticking out of the controller case. The flash upgrade included a pseudo-motor idle function that helps keep the chain semi-tight when letting off the throttle, helping to reduce chain slap. The amount of idle is increased by increasing the PAS level.

Performance into a 15MPH wind flat ground 55v at full sag during these observations.

Throttle only in PAS 5 and the biggest cassette gear of 34T gives 25MPH at 800 Watts; over 30+MPH at 1200 Watts. Full throttle made the LUNA Dire Wolf battery icon go red so I did not hold it there long but it was very fast acceleration and speed.

PAS 5 ghost pedaling and the biggest cassette gear of 34T gives 16.5MPH at 500 Watts; 24T gives 22.5MPH at 500 Watts.

In PAS the speed controller would stick to a MPH level and increase or decrease the Watts to maintain that speed; almost like a governor.

The BBSHD never got too hot to hold your hand on the motor or the controller. The motor never got hotter than 110 F.

Overall the Luna Ludi V2 is very good. It’s $ well spent even if just considering the battery range extension. If you are looking to scooter throttle only you won’t be disappointed in acceleration and top speed. As a PAS ghost peddler, it does not seem that different from the stock Bafang controller loaded up with Karl’s Sauce Settings. VESC app analytics dashboard looks cool but I don’t have an Android device nor the time to play around with those features. Luna warns not to change parameters on the controller without considering the consequences and locked out some of the most dangerous ones to the motor and rider.

P.S. At the time of publishing another field weakened BBSHD after market controller has burst on the scene. Enthusiasts of ASI BAC 855 have banded together via Discord collaboration to present a potential product challenge to Luna Ludi V2. The High Voltage team of Captain Codswallop, Mike and Greg bring a formidable grass roots business plan. I’ve done business with Captain on 3D printing for ebike items and was blown away at the exceptional level of quality and customer service. Captain told me High Voltage is “…new to the market but are providing a high quality product that customers are very happy with…focus…on customer service and quality. We are looking to expand to other motors in the near future.”

The High Voltage brand graphic to look for on authentic products:

BBSHD Performance Settings (slightly refined)

In BBSHD Programming for the Pedaling Cyclist, I laid out what my preferred settings were for my ebikes. I have settled upon them after a fair bit of tinkering over time. Since that was published, I have made some refinements.

I’m going to skip all the background I went into before. None of those details have changed. I’ll just note what I have done, and what it seems to accomplish.

Remember, There is no one perfect suite of settings for the Bafang BBSxx series of motors. Most likely, your perfect setup will take a bit from here and a piece from there to give you exactly what you want. Use what you see here as a basis for your own experimentation.

In fact, I don’t even have a single flavor I stick to as you will see below.

The Basic Screen

From then to now, I changed nothing on this screen, and I’m only showing it here to give you a complete settings reference in one place.

Figure 1: There actually is one change from the past but its only visual: the 30a current limit. The screen said 25a last time and that was not something I ever stuck with.

The Pedal Assist Screen

There are several changes here, all geared to toning things down and making behavior more gentle. I have two versions of this screen in play on different bikes. The first is the more general-use, but the things I get from Version 2 could be very desirable on any bike.

I can’t say enough that there is no one best choice of settings for your BBSxx motor.

Version 1

Figure 2: Before on the Left, After on the right

Pedal Sensor Type

Ignore this one unless you are in the mood to play around and see whats what. Some motors come programmed with BB-Sensor-32, others with DoubleSignal-24. This is something I just leave as-is depending on what the motor originally came with. Frankly its not a setting I know much about so I don’t fool with it.

Start Current

This has been reduced to 4 from 6. Start Current dictates how much juice goes to the PAS system when it initiates. A lower number means a lower ‘jerk’ on the drivetrain as the PAS system engages. This is a percentage number, so we are going from 6% to 4%. Restated, that is from ‘very gentle’ to ‘mouse-fart’! Still, as small of a change as is indicated by the numbers, its a noticeable decrease. Bear in mind I am riding some pretty big fat and cargo bikes and when starting a bike with a heavy load, a little less is much more.

Also don’t forget no setting is an island unto itself. These things taken together make up a whole, and its that whole that matters.

Start Degree

This has been increased from 4 all the way up to 10. Start Degree is the number of signal points that are crossed (as you turn the crankarms) before pedal assist engages. A full rotation of the crankarms equals 24 signals, so I have kicked up the pedal assist engagement from a 1/6 turn to almost a half-turn.

This comes in handy when I am at a stop light, but I stopped smart, several car lengths back from the actual edge of the intersection. I can then stay in the saddle, balanced with feet on the pedals. I slowly turn the crankarms a bit at a time to maintain my balance and crawl forward. If I do it right, the light turns green before I reach the edge of the intersection, whereupon I can hit the throttle and move forward without having to dismount (and then re-mount) the bike. If I decide not to use throttle and pedal my way out, I’ll need about a half turn to re-engage assist, and when it comes on it will be a very gentle ramp-up in part thanks to the new lesser Start Current above.

Current Decay

I have set this to maximum now, meaning the system pretty much doesn’t want to cut back power as my cadence increases; virtually disabling the cut-back feature from the Basic screen, which conserves power (if you can spin the crankarms superfast, you don’t need assist). This is a setting I will very likely continue to play with. If I set it to the minimum of 1, then the motor will aggressively reduce the provided power as cadence increases. A lower setting is much more in tune with the pedelec ‘philosophy’ which I usually stick to. So don’t be too surprised if you come back in a month and this text has been supplemented with talk of a different, much lower setting.

Why did I change it? Just playing around. I’m leaving it here to illustrate that these settings often interact with one another in some big ways.

Version 2

Version 2 is a riff on Version 1 above. Its what I use on my 2wd/awd Bullitt cargo bike.

‘Before’ on the left is the Version 1 ‘After’ screen just above in Figure 2. On the right is Version 2

Slow Start Mode

The slow start mode – the strength of the initial punch the motor gives out when it fires up – has been turned down a notch to ‘2’ from ‘3’, which was already a low number. I have noticed the bike this is used on has a noticeable, audible clunk when the chain engages the upgraded, 36T internal ratchet mechanism of the DT Swiss 350 steel cassette body. Every time I hear that clunk is a time the hub gets beat on. Even if it was already a reduced amount, I wanted to notch it down further. This is a good thing on a heavy, often-laden cargo bike, and its probably not such a terrible thing for any ebike.

Start Degree

In Version 1 I have this set so that there needs to be just under a half rotation of the cranks before the slow-start of pedal assist engages. When all of the settings are taken in together, it typically means pedal assist doesn’t begin to be felt until the bike crosses a 5 mph speed (If I want assist earlier there is always throttle).

In Version 2, I have reduced this to a 1/6 turn of the crankarms. The idea with all of these settings put together is that assist from the rear motor starts faster – Remember, on this bike the BBSHD is supplemented by a front motor that starts almost instantly from a stop, so the BBSHD is not trying to haul a bike up from zero on its own. On such a big, heavy bike as this cargo bike, some assist from both wheels asap is a good thing. Net result is that with two motors, I can get a good result from pure pedal assist without having to resort to the battery-sucking thing that is hitting the throttle. I start pedaling and the bike sedately glides forward even if its weighing 400+ lbs.

Current Decay

This is a full 180 from Version 1, where Current Decay is set to do as little as possible, meaning the motor is the least likely as it can be to pull power as your cadence increases. Here, it is at its next-most aggressive setting. In part this is informed by the fact that there is a front hub motor (running off the same common battery) that – if faced with a sudden power drop from the rear motor – will still provide forward assist, and in practice that means it will increase wattage as its workload increases. This is part 1 of 2 of this story, with Part 2 being …

Keep Current %

The amount of assist that is retained when Current Decay pulls power back has been reduced to 30%. So the two settings together make it more likely that, as cadence increases, power will be reduced, and the amount of power that will continue to flow has further been reduced by 25% from its previous (fairly low) value.

Got all that? Here’s what the rider feels: Not much. Despite my characterization of these changes as ‘aggressive’, which they are if you just look at the numbers onscreen, reality is the result is muted. We’re using a little less power, which we don’t miss much, and that is going to give us a bump in range. At 20-25 mph, pedaling strong at 60-70 rpm cadence, the BBSHD on flat ground is eating about 200-250w on the typical Assist Level 4 and 225-275w at Level 5. Thats pretty light (power consumption will be more on a bike with just the BBSHD for a motor!)

If you want to have the motor back off when you demonstrate you don’t need it (if you did you couldn’t spin your legs and the crankarms) the Keep Current and Current Decay settings are your go-to’s to making that happen and reducing your power consumption.

The Throttle Screen

Before on the left, After on the right

There is just one change here, and its along the same lines as what I tinkered with on the Pedal Assist screen

Start Current

This is the same kind of effect as Start Current on the Pedal Assist screen, only it works when applying throttle. I have halved the initial response the throttle gives down to a 5% delivery.

What’s the actual effect of that? Well, in conjunction with the broadened Start Voltage and End Voltage already in place, setting such a low value lets me feed in a constant 50-100w to the motor. Its important to understand this is not an initial value that increases: This is the initial value that will output continuously at the lowest level of throttle engagement.

Lots of times, I want to engage throttle just a little bit to slowly navigate some delicate or narrow pathway of some kind; especially where pedaling might throw my balance off (remember I could be riding a loaded 500+ lb cargo bike). This lets me do that. It also means when I engage throttle, the thunk of the cassette body engaging itself is no longer a thunk at all.

So not only is the bike more controllable at a low level, no thunk means stuff lives longer!

I guess I won’t be selling this alloy cassette body on Ebay after all (400 miles on it and its easy to see what cogs I like to use)

Thats It?

Yup thats it. At this point in the development of what I like and dislike on a BBSHD setup, I’m down to the last of the fine-tuning.

Big Fat Dummy: Make It An Ebike

What is necessary to transform a Surly Big Fat Dummy into an electric bicycle? I thought my BFD series was finished until I realized I left this part out.

The Surly BFD Project Menu
Prologue
Episode 1: 138L (each) Panniers… Seriously?!
Episode 2: Big Fat Dumb Wideloaders
Episode 3: Kickstand Kaos
Episode 4: Add a Flight Deck. And a Hangar.
Episode 5: Leftovers
Episode 6: Electrification (You Are Here)

Oops?

On the surface, it seems I left a hole in my description of my Surly Big Fat Dummy build. I omitted this episode and thought I was done. In my defense, there are zillions of BBSHD installation tutorials out there, and I have described a BBSHD install myself – on a cargo bike no less – right here in this blog.

However, I haven’t done a writeup geared to THIS bike. Since this blog is dedicated to answering questions that I see asked a lot (and I have seen this one more than a few times), I’ll do something a little more focused on the BFD.

Bear in mind the bike has been in near-daily use for months already. I had to dig thru my archives for pics rather than taking them as I went along. So illustrationwise, there’s not much to see. On the flip side of that, there doesn’t need to be as the Big Fat Dummy is an easy (easy!) build.

Since I have covered this ground elsewhere, I’ll be leaving generic details out, and providing links to related content more so than I will be doing in depth step-by-step instructions.

Get On With It Already!

Yeah, yeah sure … here we go.

Step 1: Buy What You Need

This can be very simple or very involved. Especially if you are a first-timer and don’t know what you need and maybe not even what you want. In my opinion the best motor for the job is a Bafang BBSHD. I typically buy my motors from Luna Cycle, and here is their page for their kit. They may or may not be selling a battery along with that kit. I am using a different source for the pack as you will see further below.

If you buy the kit, you don’t have to worry about buying individual bits, with the exception of needing a speed sensor cable extension, and a proper chainring.

But, lets go over the individual bits. Myself personally, I just buy the bare motor from Luna, and add the parts I need to complete the installation. This lets me use exactly what I want, which is not quite possible if buying the packaged kit. Here are all my parts:

  • Bare Motor:
    Purchased from Luna Cycle here. The Surly Big Fat Dummy requires the 100mm sized motor (It will be a perfect fit). if its available you can buy the optional spacer and mounting kit on that page. At the moment, Luna is not selling the 100mm mounting kit – the only difference is some M6 bolts and spacers… you can source that yourself to the correct size if needed. Or just buy the needed parts separately. Go ahead and accept the 46T chainring (aka ‘The Disk of Death’) as its a free throwaway item you would (should) never use.
    Secondary Source: California Ebike is a reliable alternative and one of my go-to sellers for parts, but their motors cost an additional $100 or so. Here is their BBSHD motor page.
  • Motor Mounting Parts:
    • Triangle Mounting Plate:
      This is what puts the bite on your bottom bracket to firmly affix the motor. You can buy these plates at Luna Cycle, BafangUSA Direct or Amazon.
    • M6 bolts, washers, spacers:
      Needed to affix the Triangle Mounting Plate, these are commonly available. If you work on bikes you probably already have them in the garage. If you buy a mounting kit they may have them but in all cases I recommend you do not use them and instead go out and buy stainless hardware.
    • Lockrings:
      I use two inner rings stacked atop one another. If you like, you can buy the more conventional inner and the aesthetically-pleasing outer. More on the reasoning behind the choices below. Buy the rings at Luna Cycle, Bafang USA Direct or Amazon.
  • Speed Sensor & Cable Extension:
    You will need the sensor (which integrates a length of cable to plug into the motor), the sensor magnet and an extension thanks to the Surly Big Fat Dummy’s long tail. I have seen builders route the sensor to the front fork but by necessity this puts the sensor inside of the tire rim’s width, which makes for issues taking that tire off. Put it on the back where it belongs and forget about it. I described the sensor in a fair bit of detail here. Don’t mess with multiple magnets unless you feel a need to experiment, but I do provide a link to what I think is a lighter weight, superior magnet that you may want to substitute for the Bafang wheel weight that comes with their sensor. The speed sensors themselves are available in a wide variety of places, cheapest at Luna but also at California Ebike and many other sources. You can get the speed sensor extension anywhere you can find the speed sensor. California Ebike or Bafang USA Direct or many other sources, including Amazon with Prime Delivery. Notice all of the options I linked are different lengths. Measure the gap you have when you are routing your cabling and decide which one you want, accordingly.
  • A Proper Chainring:
    I am going to skip most of the detail here and refer you to this blog post on BBSHD chainrings. It was written with the Mongoose Envoy build in mind but the Surly Big Fat Dummy is essentially an identical set of problems and solutions. I will say this: For a combination of mostly street with some mild trail use I settled on the 46T Lekkie Bling Ring, which biases chain line towards the bottom half of the 11 speed cluster. This is the ring that has the most miles on my bike and its the best all-rounder. At the moment I am set up mostly for trails, though, and as such I am running the Luna Eclipse 42T which biases chainline heavily toward the inner half of the rear cluster, giving me good access to the inner cogs. You cannot go below 42T in the front without compromising chainline to the inner cogs.

    Note with a BBSHD, the stock My Other Brother Darryl rims and the stock Edna tires, you will not be fully able to use all cogs simply because chainline will not be acceptable for a 1x drivetrain pumping out 1000 to 1750w. You8 can do it, but the chainring teeth and maybe the chain will not last very long if you run at either extreme – say… the biggest cog and the Lekkie chainring.

    Two of the pics below show a 130 BCD adapter which really biases chainline to the lower cogs, and is best for the street. Both of these use 48T, 130 BCD chainrings. Even though most of my mileage on this bike is with the Lekkie ring, it doesn’t appear as if I ever took a picture of the bike with the thing installed.
  • Crankarms:
    In two of the pictures above you can see I used Lekkie Buzz Bars, and with their forged construction and left offset to correct the misalignment under your saddle that will happen with standard crankarms. Luna Cycle sells a less-expensive clone worth looking at if you can’t handle the price of the Lekkies. As a last resort you can also use the standard Bafang crankarms that are cheap and cheaply made, but good enough for many riders. Make sure you buy BBSHD-specific arms or they will not have the left offset.
  • Display:
    I have used many displays and hands down, at the present time the Bafang/Luna 860C is the best out there. It is fully visible in blinding sunlight and can be set to display both real time amp output as well as real time wattage. The Luna version reads battery voltage level accurately up to 60v, meaning it works with 52v batteries. Bafang versions of the 860C may not. There are many other options for a display including a low-visibility-but-clean/low profile EggRider v2. For my money the 860C is worth waiting for if its temporarily out of stock, and its my go-to for bikes I build.
  • Throttle:
    I like the basic el cheapo Bafang universal thumb throttle. Its an easy fit and unobtrusive. If you follow my lead on BBSHD settings for it, its annoyingly short throw will still be well controllable and allow for fine adjustments while riding. Buy it at Luna, California Ebike or Bafang USA Direct.
  • Main Bus Cable:
    You have options here. the main bus cable is available in short and long lengths, and there are also extensions available. However nothing fancy is required on the Surly Big Fat Dummy. You can buy this standard one from Luna or many, many other sources. If you opt to use Magura MT5e brakes, California Ebike has a specially modified harness to plug in the red Julet cutoff connectors the MT5e uses. I am using this bus cable and MT5e’s, myself. NOTE: If you opt to keep the SRAM hydraulic brakes you will not have brake-actuated motor cutoffs. This is no big deal. They’re nice but the stock brakes can overpower the motor in a pinch. If you like, you can invest in some hydraulic cutoff conversions that involve gluing on a magnet to your levers and strapping on some wires. the alternative is a brake upgrade (not a bad thing, but not cheap, either).
  • Installation tool(s):
    Using one of the many Bafang-inspired toy wrenches to install a BBSHD is a cruel joke on the inexperienced. You have to use a proper torque wrench and special socket to do the job right, where the motor doesn’t move. I’ll leave the torque wrench choice to you (I use a Wera B2). The socket you need for the inner ring is often out of stock. Buy it here at Luna Cycle or hunt around… its available elsewhere if you look. The tool for the outer ring can either be hand-tightened – if you must – with a stainless steel version of the cheesy Bafang wrench. I bought this one on Amazon so I know it fits. But it is absolutely a sucky solution. Better is to use a 16-notch bottom bracket tool that you can fit onto a torque wrench and do a proper job of applying the manufacturer’s torque spec, written right on that outer ring. Note if you use two inner rings you do not need the special outer ring tool.
  • The Battery:
    There are a bunch of different ways you can play this. Among others you can plant one on the bike on the framework just behind the seatpost. At present mine is in the triangle in a bag. My seize Medium frame can just barely hold this 21ah, 52v battery from Bicycle Motorworks. ‘Barely’ means after I have added some padding. I also keep the battery in a quick-detach bag inside the triangle. I described the quick-release setup with pics in detail here.

    I’d like to have more room for padding, so I am exploring a shift to that framework as an alternative. We’ll see as its a big change.

Step 2: Remove Stuff

OK so you have all of your parts for the motor… Time to take things off so you are ready to do the installation. Its a simple list: Remove the crankarms, bottom bracket and chainrings.

You’ll also want to pull off one of your handlebar grips in preparation for installing your throttle. Which one depends on how you want to set up the bars. You will also likely want to loosen up and shift around your brake levers and the remaining rear shifter so your throttle is butted up directly against your hald-grip, rather than the brake being there. this is a bridge you should cross when you come to it, disassemblywise.

Initially I used a Luna Wolf Pack, as shown in this picture. Thats another option for your build.

Thats it. You’re ready to install your motor.

Step 3: Install The Motor

Here again I’m not going to get too deep into the specifics of motor installation. I’ve already covered it myself elsewhere for a similar bike, and God knows there are plenty of video and written tutorials out there on the interwebs. However I will note that the 100mm motor is a perfect fit on the Surly Big Fat Dummy, which requires no spacers of any kind. Just put it in like it belongs there and clamp it down tight.

About that clamping part, I will go into that a bit:

Lockrings

I mentioned above that I like to use two inner (gray) lockrings: I stack them atop one another in jam-nut fashion where each is tightened to 100 ft lbs. Thats quite a lot more than the Bafang specification for using just one inner lockring. I am going off of installation advice provided by Luna Cycle – not in their official installation video linked above. At one time there was a supplemental vid made in their shop that discussed their learning to do this on their shop bikes. It went hand in hand with the use of a big 1/2″ torque wrench to apply the necessary force, and that wrench in turn used a specially made Luna tool for the lockrings (that sadly is no longer available, although you can see them on the site still). The use of 100 ft lbs and some additional info on it is in the link to the tool above.

I have stuck to that 100 ft lb specification and it has never let me down. I have also added to it by using a second inner lock ring rather than the ‘beauty’ trim ring that is more typically used. the number of threads needed for another inner ring is about the same. You gain the benefit of a serious jam nut holding down the first ring. Also, something we are not doing here but you can see elsewhere: If you are building an AWD bike, the use of two rings lets you mount the front wheel’s PAS ring in between the two.

I do not use the outer trim / beauty ring at all.

Lastly on the subject of lockrings, here’s a technique to tell at a glance whether the rings are loosening or your motor is shifting (or about to): Make a registration line along the frame and the lockrings. If the line ever breaks apart, something is loosening. You can tell with a simple glance down as you are mounting the bike.

See the registration mark (aka the black Sharpie line)? Also note there are no spacers needed on the locking plate under the M6 bolt on the left. Perfect fit for a 100mm motor.

Next, I’ll make note of how I did the speed sensor installation, both with the factory SRAM brakes and my later MT5e upgrade.

Using the SRAM Brakes / No Helpers

Attaching a speed sensor on a Surly Big Fat Dummy is not as straightforward as it is on a typical bicycle. In addition to the added distance – addressed with an extension cable – there’s no place to put the thing! The frame is different enough that nothing appears to work – on first glance.

Keep looking! the SRAM brakes that come stock with the bike have a weird sort of tail hanging off the caliper, and this is a handy, if unusual, place to mount the speed sensor.

I first wrapped this tail with a length of 3M mastik tape to enlarge its diameter and give the sensor more to grab onto. Then I simply zip tied it on as if it were a chainstay, and aligned the magnet as usual. These pictures show a dusty bike as they were taken just before I uninstalled the sensor and upgraded the brakes to the Magura MT5e’s.

Using Other Brakes – And a Crutch

For the Maguras, there was no such luck as the calipers have no tails or anything else I could glom onto. So I had to add something: I used a simple small handlebar extension, and built up the frame to a proper larger diameter to mount it by wrapping the frame with gorilla tape, which I then faced with silicone tape to provide a grippy surface for the bar mount. Next, I used more zip ties (!) to clamp the new ‘frame tube’ to the upper part of the Big Fat Dummy’s … superstructure. Once this was done, I had a tube close enough to the spokes to re-mount the speed sensor as shown.

What About a Gear Sensor?

Good question. Read this.

Whats With The Heat sinks on the Motor?

I’m glad you asked. Here’s your answer :-).

What Else?

Well, a bunch I suppose if you were looking for a bolt-by-bolt conversion tutorial specific to this one bike. But really, between the other pages already on this site and the links I have given off-world up above, you’ve got everything here that you need to buy – and build – your own.

So have at it!

Dual Motor AWD Electric Bikes – Case Study: Larry vs. Harry Bullitt Cargo

After multiple strong AWD builds, I used this one to prove a unique concept: You don’t need big power to get big AWD benefits.

AWD Ebikes Menu
AWD. OMG. WTF!
Case Study – Flatland Fat Bike Commuter. Hub+Hub
Case Study – Alpine Road & Trail. Hub+Mid Drive
Case Study – Low-Power Cargo Beast. Hub+Mid Drive (you are here)

The Lizzard King

  • 500w, 25a geared Bafang G020 front hub motor
  • 30a BBSHD mid drive (rear motor)
  • 52v, 32ah single battery, skateboard config (box under cargo floor)
  • KT and Bafang displays
  • 160 Nm rear, 45Nm front
SIDEBAR:
This 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 16 mph. But from 17+, it starts scaling 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 23-24 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 up again. But rolling down the street on the flats, the front motor takes itself out of the picture. Its time for…

… The rear motor to kick in. As noted, pedal assist does not engage the rear motor until it crosses past 5 mph. So when the front motor is eating the most juice, the rear motor hasn’t even started. As the mid kicks in and spools up, the hub begins making its graceful exit.

The two motors never really run hard together at the same time, unless climbing a hill. Then you can see watts climb on the front rather than fading away. Cruising at an energetic cadence around 24+ mph , you are on the single rear motor, being given a small boost from the front motor (remember those 37 watts?).

With the two motors staying out of each others’ way, 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 kess 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 mash the rear throttle the BBSHD will, as usual, peg the output 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 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.

And despite the capability of the bike, reality is it rides more comfortably around 20 mph. So power consumption is lower still simply because of the type of bike it is. But the big takeaway is its lower power use is lower across the board. It was an unexpected gain in efficiency, but looking back on it, it should not have been. The benefit was hidden by my hard use of the other bikes.

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. 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.

Dual Motor AWD Electric Bikes – Case Study: Fat Trail and Hill Climber

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.

AWD Ebikes Menu
AWD. OMG. WTF!
Case Study – Flatland Fat Bike Commuter. Hub+Hub
Case Study – Alpine Road & Trail. Hub+Mid Drive (you are here)
Case Study – Low-Power Cargo Beast. Hub+Mid Drive

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.
  • A professional sprinter/mutant is capable of pumping out almost 1000 watts, but only for about a minute or two. Thats not enough power to make a slice of toast.
  • 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…

SPOILER ALERT: It worked unbelievably well.

BBS02 and BBSHD: Do I want a gear sensor?

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.

Dual Motor AWD Electric Bikes – Case Study: Twin Geared Hub Commuter

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.

AWD Ebikes Menu
AWD. OMG. WTF!
Case Study – Flatland Fat Bike Commuter. Hub+Hub (you are here)
Case Study – Alpine Road & Trail. Hub+Mid Drive
Case Study – Low-Power Cargo Beast. Hub+Mid Drive

The Great Pumpkin

  • 2 x 750w 80Nm geared Bafang G060 hubs
  • 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.

Gallery

And THAT is my rain or shine daily driver.

Dual Motor AWD Electric Bikes (the good and bad)

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?

AWD Ebikes Menu
AWD. OMG. WTF! (you are here)
Case Study – Flatland Fat Bike Commuter. Hub+Hub
Case Study – Alpine Road & Trail. Hub+Mid Drive
Case Study – Low-Power Cargo Beast. Hub+Mid Drive

In the Beginning…

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.

  1. The powered wheels would fight for supremacy between each other.
  2. It is essential to match the power to both wheels but impossible to do so.
  3. Even slight differences in wheel circumference between the two would make terrible things happen.
  4. 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, putting more power to your back wheels is not 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 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 you can ride through just got a lot wider.

If on the other hand if 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 an exotic sports car. Powered traction is delivered to the ground across twice as much rubber. 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 feels wonderful, like 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 its effortless for the bike to do what it is 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, especially with 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.

  1. 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.
  2. 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.
  3. 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. 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 their hubs need no maintenance. You will also get slightly increased 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 them do this. When I look, I see the sort of features – and mistakes – from when I first started kludging AWD bikes together. The reality is, 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 a proper AWD bike coming from a commercial vendor unless one goes on a mission to sell a great bike and not take such a high profit margin.

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 this 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 up top.