In the search for a mid-drive motor kit I’ve found that most distributors neglect to state the size of the crank arm. The few that do have chosen a size that’s optimum for people 5’9" or taller.

The average US woman is 5’4", and the average Asian man is 5’7". These groups are being discriminated against in the market of DiY mid-drive motor kits.

It’s a one-size fits ~20% of the population scenario, roughly, and only one size is offered. Some kits are standard enough that it’s possible to buy a separate aftermarket crankset, but the specs are undocumented and this also entails spending $100+ more and then wasting the stock cranks after spending upwards of $500 on the kit. The industry needs to get its shit together.

model bottom bracket req. crank size optimum rider height notes
AFT n/a (straps to frame) n/a n/a shitty tor-hostile site
Bafang BBS02 68-73mm ? ?
Bafang BBSHD 68-73mm, 73-100mm, 120mm 175mm 5’11"
Bikee Bike ? ? ? uses Sony batteries (unethical!); app is iOS & Google Playstore only; shitty tor-hostile site
Binova Flow ? ? ? no useful info on website and their store blocks Tor. ~$2k
CYC x1-pro 3000w 68,73,83,100,120mm 170mm 5’9" same as GNG x1-pro? chain or gear drive; app is iOS & Google Playstore only
Cyclone 3000w 68-83mm, 95-120mm 170mm 5’9" $430
Ecospeed side-drive? ? ? for recumbants; dead
Ego side-drive? ? ? CloudFlare site
L-faster 68mm (+100mm for 750w motor) ? ? 250w,350w,500w,750w,1300w; chain drive & integrated versions; integrated speed sensor; $345 for 750w
GNG 2016 Premium belt 68-73mm 170mm 5’9" CloudFlare site
GNG 2019 3000w Cyclone Premium 68-73mm, 83-120mm ? ? CloudFlare site
GNG 2019 450w Cyclone Premium 68-73mm, 83-120mm ? ? CloudFlare site
L-R two stage 68-100mm ? ? $745; broken contact page
Luna Deluxe Mini Cyclone 68-83mm ? ?
Pendix 68-73mm ? ? 250w; >$1k
Tongsheng TSDZ2 68-83mm, 68mm,100mm,120mm 170 5’9" crank arms have an absurd Q-factor and should be replaced anyway. They are compatible with Bafang & Shimano Steps FC-E6000
Xing ? ? ? shitty tor-hostile site
Xofo 68mm ? ? Bafang knock-off? broken mfr site

The product information available is lousy all around. If anyone finds data for any of the above question marks, please post and I’ll update the table. These are the ideal crank specs (neglecting special circumstances like crouched over racing positions):

rider height optimal crank length (mm)
6’0" (1828mm) 177.5
5’11" (1803mm) 175
5’10" (1778mm) 172.5
5’9" (1753mm) 170
5’7" (1702mm) 165
5’5" (1651mm) 160


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