Fat Bike + BBSHD: Two Great Tastes That Go Great Together

Editor note: This was posted by user Arcanum in the new Electricbike.com forum section “Building Directions” where builders document what kits and parts and what donor bike they used and how they put it all together to get their  DIY bike electrified.  In this case it is the 1000w Bafang BBSHD and a Moose fat bike. You can see this entire build thread in our forum by clicking here. 

I bike commute year-round in Rochester NY. We get a lot of snow in the winter (usually). I’ve used a Kona Dr. Dew with studded tires in the past, but this past Spring I bought a fat bike. It was good, but as fat bikes can be, it tended to be a bit sluggish. Rochester winter did not improve this, though the fat tires did make the slush and mush and frozen bumps and ruts easier to manage. Riding to work and to get groceries during the winter was still a slog. So I thought, more torque from an electric motor will surely cure what ails me.

After doing a bunch of research and spending a bunch of money, I did the conversion about a few weeks ago. A BBSHD and 48V pack isn’t the most powerful conversion ever, but it’s got quite a bit of get-up-and-go with the small 30T chainring, and the work was relatively straightforward to do. I’ve ridden it for probably a couple hundred miles, and at low-mid assist levels it lets me make good time with an enjoyable level of exertion.

Moose Bicycle Moose XXL (2015) fat bike

Aside from the top tube and water bottle mount position making battery mounting difficult, this was a great donor bike. No chainstay or other spacing problems, unlike some fat bikes. The motor slotted right in with no problems. Note that this bike appears to be nearly identical to the BikesDirect Boris.

Bafang BBSHD 120mm mid drive kit

A 1000W (nominal, underrated) mid-drive motor powered by a 48V, ~25A continuous, 13.5 Ah pack. I say underrated because people with bigger balls than I have figured out that the motor is significantly overbuilt and will quite happily run at 1500W continuously with no problems. I went with a mid-drive because the bike’s gearing makes it more efficient at delivering power, better at climbing hills at speed since the bike’s gearing lets you take better advantage of the motor’s torque, and it generally feels like less of a kludge.

Lunacycle 48V 13.5Ah Shark battery pack w/ upgraded charger

~25A continuous output. The motor will quite gladly take 30A@52V, but I figured I didn’t need that much juice for my purposes. Bought the better charger due to more features, and not wanting my apartment burned down by a cheap charger made out of Chineseium.

Lunacycle Mighty-Mini chainring

Moar torque. At moderate pedal assist settings the BBSHD will actually spin this ring faster than you can pedal. I may swap it for a 42T ring.

Bafang C965 display

Bafang BBSxx Left Thumb Throttle

XT90-S spark resistant connectors

Water and spark resistant. I went with these instead of just crimping the wires because this is the hard disconnect for the battery until I buy a suitable button or switch.

Universal magnetic brake sensors

These cut the motor when you pull a brake lever. I have hydraulic disc brakes, so the mechanical levers that come with the kit were no good to me.


Original Bike


I soldered XT90-S connectors to the battery and pack leads, then potted them with E6000. I ride in rain and snow and salted slush, so I’m a bit paranoid. Had some power issues at first due to the E6000 getting on the contacts, but that cleared up once I scraped it off.

Pedals and cranks off

Trying to remove the bottom bracket.

Bicycle Mechanic uses LEVERAGE!

It is super effective!

First I tried removing the bottom bracket cups with the bottom bracket tool and an adjustable wrench. No dice, even with PB Blaster. So the next day I went and bought additional tools.

I loosely bolted the bottom bracket tool in place with an M8 fine thread bolt and tried just a big wrench, then upgraded to a big wrench and breaker bar. The bolt keeps the tool from popping off the teeth in the bottom bracket cup. After loosening the cup enough to turn the cup, you want to remove the bolt. If you leave the bolt in place while you remove the cup you can strip out the threads inside the crankshaft, thus ruining the bottom bracket. More information about the bottom bracket removal method I used here.

After that, most everything else was easy, though running and securing the cables was time consuming. Just follow the instructions in the manual and you can’t go far wrong.

Drive unit, itty bitty 30T chainring, and crank arms mounted.

Cables run and battery pack temporarily mounted with zipties.

I ran it with the battery mounted via zip ties for a week or so, then built a proper mount for the pack. For reference, the rear rack is an Axiom Fatliner, one of a very small number of rear racks that will mount on a fat bike that supports 5″ tires.

Aluminum bar with holes drilled.

The beginning of the permanent pack mount. Sadly the pack doesn’t quite fit on the downtube. 3′ of aluminum bar can be acquired at Lowes for about $15, if I remember right. Not a lot of money.

Bar bolted in place.

I had to correct a hole location as well. At first I tried putting some inner tube rubber around the bar. I was trying to prevent rubbing and wear, but realized it was both pointless and creating extra aggravation in mounting the pack. I’m probably going to have to go back and remove those scraps of rubber; I think they’re preventing those bolts from staying as tight as they should.

Pack mount bolted in place.

Spacers to keep it stable.

Pack mounted.

Completed (mostly) bike

Evaluation and Future Work
It’s got plenty of get-up-and-go, and in good conditions has a range of about 34 miles. I still want to wire in a battery disconnect button, a good power meter, and some lights driven off the main pack. I’ve already ordered the lights: A Schmidt Edelux II DC 6V-75V headlight (near the bottom of the page) and a Busch & Muller Toplight Line taillight (about 2/3rds down). You can see the headlight pattern here, about 1/3rd of the way down the page. The lights aren’t cheap, but the pattern is fantastic; as a year-round, day-or-night rider, I take my lighting very seriously.

Regarding the linked battery disconnect button: I emailed the site to confirm that it would work. They said it should, but the MOSFETs aren’t very high quality and may burn out at the voltage/amperage involved. I’ll probably buy one anyway and see how it goes. It would be nice, though, if a respected store in the ebike world, one that already contracts the manufacture of their own electronics, released a similar button or switch that was properly designed for the rigors of moderate-to-high-powered ebikes. Ahem.

Ride Report
I can’t say I have much experience riding ebikes. This is my first, in fact. However, I’m quite enjoying the combination of a fat bike and a BBSHD. The motor has pretty well cured the innate sluggishness of the bike and then some.

Most of the time I’m cruising at 12-15 mph while pedaling in PAS level 3 (of 9). I’ve had the bike up around 25 mph in PAS 8 and a high gear. That’s just leaning on the throttle; I find that pedaling along is pretty well out of the question at that speed with the Mighty-Mini chainring.

Range using my standard cruising speed in not-too-cold weather is around 34 miles. Shortly after that the power coming from the pack gets low enough that the motor starts acting like a misfiring two-stroke lawnmower engine. The whole system will also run gamely along in subzero (Fahrenheit) temperatures, but range is reduced substantially. If I were to build my own pack from scratch, I’d consider building in a heating system.

Ride-wise, it’s stable and mostly surefooted across anything from rutted and bumpy ice to fresh powder to the nasty mashed potato mush that I always hated on my skinnier tired commuter. Winter riding is considerably less stressful on the fat bike, and the ability to use the bike’s power and weight to plow through and over mounds help as well.

All that said, it’s not 100% sunshine and roses.

The dense snow of thick drifts can still throw it off and cause it to slide, though, and there’s only so much you can do about 18+ inches of heavy, wet, fresh snow.

I’ve been seeing odd battery and/or controller behavior right after turning the bike on: Sometimes, and only right after turning the bike on, shortly after I start pedaling voltage from the pack will briefly drop to near-nothing, then come back. That seems to confuse the controller and put it in a higher PAS level than it was previously set, though the PAS level on the display stays the same. If I change the PAS level myself after that happens, everything goes back to normal. It’s not a huge problem, but it’s weird and disconcerting.

On hard surfaces, at a certain speed that depends on tire pressure and the weight the bike is carrying, a weird harmonic bounce gets going, causing the whole bike to bob up and down as it goes along. It’s not the result of pedaling, either; it happens even coasting or relying entirely on the throttle. The bike probably would have done it without the electric motor, I just rarely had it going fast enough and with enough weight before. It’s mostly just annoying.

A bigger issue that that the extra weight of the electric hardware seems to make the bike more prone to be unsettled by certain surfaces. In particular, large stretches of a mildly undulating surface, like a large and poorly smoothed road patch, can upset the steering. Likewise if the front tire doesn’t quite go all the way into a sunken section of the road (such as a drainage grate) and instead rolls along the edge. This occurred before the electric conversion, but the conversion has made them worse/more noticeable.

Despite the few issues, I’m still very happy with the conversion. It’s quick and stable and has a good usable range.

Example Ride
We’ve had a shockingly mild winter so far here in Rochester, but we finally got a bunch of snow Tuesday, so I was finally able to use this beast for what it was meant for. Work was closed due to the snow, so I decided to ride out to brunch, and made a video of the ride. She worked like a champ, stable, powerful, and confidence-inspiring. Up until I encountered a big pile of snow left by the plows, anyway

(The camera was mounted on my handlebars, hence the odd motion and it not looking left and right at intersections. Also, the motor is louder in that video that it sounds to me when riding.)

Finally, I want to say that Tom and Lunacycle were very helpful in answering my questions and sanity checking my parts selection, even when the questions were a bit silly.

Hopefully this write-up will be useful to others. If anyone has any questions, I’ll be glad to answer them.

Written by Edward Huyer Febuary 2016

See entire forum thread here

Eric has been involved in the electric bike industry since 2002 when he started a 6000 square foot brick and mortar Electric Bike store in downtown San Francisco. He is a true believer that small electric vehicles can change the way we operate and the way we think.


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