Originally Posted by
alias5000
Thanks for this. That's unfortunate regarding 20 vs 700C. Does this apply generally across the board, or is this bafang-specific? Does bafang offer a torque option (they have this bottom bracket that senses something - is that torque? Does it use that for pedal assist?)
According to the cargo bike manufacturer, a front hub system would not work as the fork is not rated for that load (and they say that there have been actual accidents from people ignoring that advice).
yeah, can't use a 700c motor in a 20" wheel, or vice versa. (well, I do, so there is that).
For the motors I use, 32km/hr is about 200 rpm in a 700c wheel, and probably 330 rpm in a 20" wheel. The no load motor speed is determined by windings and is a fixed thing. So, with a major brand (MAC, Bafang, Cute), you have the choice of # of windings - which determines the no load speed. Generally you match that to the wheel size (and load you will be carrying).
If you want to use the same motor for 29" and 20", you are gonna need a mid-drive - where you can use chain gearing to match the speed of the motor/wheel.
I'm not sure that a mid drive is more vulnerable to winter. Certainly it is gonna get a LOT more road spray, so there is that. I use a hub motor in Ontario conditions, and it works for me. The best thing (by far) is that I can use super efficient summer slicks or super inefficient studded tires (600 studs total) and cruise at 32km/hr either way. It really doesn't make much difference. I guess that my range might be reduced in the winter (with the cold and inefficient tires), but I never really run a battery dry in the winter. Wind chill can be an issue though. ;-)