Aftermarket Mid-Drive Q-Factors & Axle widths

[Mark Pace]

Is there a handy chart or database anywhere that lists the bb axle widths of various mid-drive motors? Not the frame BB widths they fit, but of the axle the cranks fit on.

Unboxing and installing a Bafang M225 motor (which I think is otherwise known as a BBS02 in a '250W' configuration) I was sorry to see that its axle measures a whopping 174mm long, which is right in the middle of what most fatbikes with 4 to 5" tires use. It may be as short as usually possible on the right, but the left is much longer than it needs to be. When I last installed a 500w iteration of the same motor, over a year ago, I don't remember it being so very wide, but maybe it was.

With the supplied Bafang crankarms (90°, but with a slight offset) the 'q-factor' (aka tread) will be close to 195mm, which looks pretty silly on a bike with 45mm tires and 90mm wide chainstays (where they are closest to the pedals.) With the slimmest, straightest, most zero-offset arms I know of (Schumpf, and only in their 170mm length) that 195 can be improved by maybe 10-12mm, but that's about it. With any arms having substantial (and nowadays typical) offset, it is really ridiculous.

So my 2nd question is, does anyone know of any square taper arms in any lengths shorter than 170 that are 90° with 0 or near-0 offset? I have some 160's, but they stick out so far on this motor that you can just about put your fist between the chainstays and crankarm ends.

 

[Chalo]

Unicycle square taper arms are traditionally very square and come in short lengths. I used 152mm ones on my BBS02. Steel arms seem to have the least offset.

United Black Cotterless Cranks -150mm

United cotterless crank arms for distance riders. 102-mm, 8-inch, 12-inch. 110-mm & 127-mm, 20-inch wheel. Req. crank puller tool from dropdown menu.

www.unicycle.com

 

[Mark Pace]

Thank you, Chalo. Those are some very good lengths, especially for recumbents. I'd rather have them in aluminum, but may become desperate enough to use those.
I think I will try some of their pretty ISIS cranks in a 114 for another customer, but am not sure if they will actually fit her Bosch Active Line Plus motor. I don't know which version it is, but the crank bolts are only 10mm -- neither the 12 or the 15mm that I see as the only currently available replacements. If it fits the spline, it still may not clear the motor on the right, but if that's not too far off, I think I can remove several mm's of material on the inside without any risk of her ever breaking it. If it is the 'mini' type of ISIS, I don't see any of those in short lengths, anywhere. I wrote to Bosch on the matter about 32 hours ago, but they have yet to "get right back" with me.