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; ecospeed.com 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 |
| ? | ? | ? | 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 |
(source)
I didn't know this was a problem! I'm really sorry that this is the case and I hope that you are able to find a kit that works with your body without having to spend even more on a 2nd crank arm