This is my first build, an e-Fatbike. I installed a BBSHD and 20 AH Panasonic PF Triangle Pack, both from Luna Cycles, onto a Motobecane Sturgis Bullet. I’ll try to provide enough details and photos to make the process clear.

This is not the first such BBSD/Sturgis build – MountainTime posted a very similar build at Endless Sphere a couple of weeks ago. I owe him thanks for his advice and help with dimensions, such as confirming that a medium frame could fit my triangle pack, and that a 100 mm BBSHD would not quite fit this frame without shimming and an offset left pedal.

This bike is a blast to ride. I put a 30T Mighty Mini sprocket on it from the start. I only have 5 miles on it, at sunset tonight, after finishing up the build. I was in PAS1 most of the time – it is the highest PAS setting I can keep up with, pedaling for real to help. I was not disappointed by how quiet and powerful this drive is, and I’m nowhere maxing it out yet. Tire knobs drown out the drive noise, which itself is very smooth and pleasant sounding. Sweet!

Frame size is 17.5″, Medium. I’m 6’1, but I wanted my 5’4″ daughter and wife to be able to ride it once in a while. It fits me fine, and they can stand over the frame. Barely. I cut one inch off the seat tube so it can go low enough for them. I set it to the full recommended extension, and it fits me well. Inseam 36″.

I chose that model bike in particular because it comes with a ($600+) Bluto fork and has a relatively open frame triangle for battery clearance. It also comes with nice components such as Mulefut tubless-ready clincher wheels and Snowshoe tires.

I chose the 120 mm BBSD kit. I wanted the crank arms centered on the frame. The right side pedal clearance is set by the motor, and nearly all the shimming was on the left side, so a 100 or 110 mm kit would have resulted in the same pedal spacing anyway, if I added a offset LH crank arm to get the pedal spacing symmetrical. You need to cut off about 5mm from the front derailer mount on the frame to center the install (motor just touching rear triangle) and that gave me the best chainline. That 120mm kit fit very nicely, with only shimming, once the frame was slightly modified.

First of all, removing the stock crank arms was not easy! I bought a puller tool that would thread into the arm, but the crank is hollow, so there was nothing to push on with the puller’s center bolt. I wound up heating the right crank arm to maybe 200F, and then pounding on a steel rod inserted through the crank from the left, hitting the puller tool hard enough to drive the right arm off. LBS said it should be ‘self extracting, no tool required. Well, I don’t agree. My stock bearings would probably click if I tried to use them again. Not recommended, but I didn’t want to wait a day for the shop to do it.

This tool fits the outer nuts on the stock crankset, but only after cutting off the ‘rear cassette removal’ half of the tool. With that 2nd tool still attached, it didn’t fit over the splines on the crank. Not hard to cut with a bandsaw, but I’d advise buying the same socket style WITHOUT the bonus tool on the back of it:
https://smile.amazon.com/gp/product/…?ie=UTF8&psc=1

For the inner nut, I used a Fox spring perch wrench from a snowmobile/dirtbike sized shock. I needed a 12″ total length handle to get that one off. Not bad.

So, how’s the chainline? Not bad! Centered, at least. But there is a fairly big zigzag at the extremes. Tire clearance is real good to the chain. I have not had any trouble with shifting, after re-adjusting the shifter cable length. I have not applied full power in top gear at high speed yet, though, either. I have floored it in low gear, no issue.

There is room for a bigger chainwheel to clear the frame, without making the chainline worse. I know there are a couple of 42T out there, like the Luna Eclipse. But they move the chain inboard. Perhaps too much, as this lines up pretty well in #5&6 gears (10 speeds). I think I’d like to try to put a 36T on there for slightly higher gearing. But I can’t find an adapter to fit the BBSHD for standard chainrings:

OK, that’s about it. Quite a marathon post. I’d be happy to answer any questions. I converted these wheels & tires to tubeless. I can show that process if anybody is interested. I used the Mulfut tape intended for these wheels, and Stan’s sealant. It’s pretty easy to do, and not hard to find the info elsewhere.

Only one thing surprised me about the BBSHD design. When pedaling with the motor off, the pedals seem to spin the gears inside the drive unit, which adds a noticeable amount of drag. It does not spin the motor, just the gears. I expected the pedals to be able to turn without spinning any of the internal drive parts, more like a regular bottom bracket. I’m not certain it is supposed to work that way, but I suspect it is by design. I haven’t seen anybody else mention it, though. I didn’t disassemble the motor to confirm this 100%, but I can feel the drag, and it feels like gears meshing, that kind of vibration. If it’s not the gears, then the clutch is rather draggy. It’s not enough to be a problem when pedaling only, probably not noticeable; I just found it interesting.

Turning the rear wheel backwards DOES spin the motor, with significantly more drag, but I don’t plan on riding backwards very much, so no big deal there. But it let me confirm I wasn’t feeling motor drag with the pedals.