Can't shift to lowest gear with Bafang mid-drive motor installed

SdotC

1 mW
Joined
May 13, 2022
Messages
10
Location
Calgary, Alberta
I have a Bafang BBS02 mid-drive motor installed on my Cannondale Quick 4 hybrid with 9-speed cassette and Shimano shifter. It works really well, EXCEPT the the shifter cannot raise the chain to the largest (lowest gear) rear sprocket. The drive sprocket is the standard 44-tooth one that was supplied with motor. It is not a great hinderance unless I ride without the motor where I want to use the lowest gear.

Is there a solution for this, such as a concave 44-tooth drive sprocket that would allow the shifter/chain to travel the the whole range of 9 gears at the back?
 
SdotC said:
I have a Bafang BBS02 mid-drive motor installed on my Cannondale Quick 4 hybrid with 9-speed cassette and Shimano shifter. It works really well, EXCEPT the the shifter cannot raise the chain to the largest (lowest gear) rear sprocket. The drive sprocket is the standard 44-tooth one that was supplied with motor. It is not a great hinderance unless I ride without the motor where I want to use the lowest gear.

Is there a solution for this, such as a concave 44-tooth drive sprocket that would allow the shifter/chain to travel the the whole range of 9 gears at the back?

Are you using the stock chain? If so, it may not be long enough to go from the stock 38T to the BBS02 44T with the largest rear cog.
 
If the front chainring is larger now than it used to be, then you'll need to add half as many links to the chain as the difference in number of teeth for the largest gear in front, between the smaller one the bike used to have, and the larger one it has now.

Or change the front chainring to one that is the same number of teeth as the one the bike used to have.

If you also changed the rear gearing cluster to a larger number of teeth, you'd need to *also* add another half as many links to the chain as the difference in that number of teeth as well.

(each link referred to here is the two hinged parts, the "skinny" one and the "wide" one, and covers two teeth, so you only need to add 1 link for every two added teeth).


SdotC said:
I have a Bafang BBS02 mid-drive motor installed on my Cannondale Quick 4 hybrid with 9-speed cassette and Shimano shifter. It works really well, EXCEPT the the shifter cannot raise the chain to the largest (lowest gear) rear sprocket. The drive sprocket is the standard 44-tooth one that was supplied with motor. It is not a great hinderance unless I ride without the motor where I want to use the lowest gear.

Is there a solution for this, such as a concave 44-tooth drive sprocket that would allow the shifter/chain to travel the the whole range of 9 gears at the back?
 
FME, the right BBS02 crankarm is displaced about 10 - 15 mm farther from it's chainstay than the left. You can use a Lekkie chainring, which brings the chainring in enough to access all the gears. Also a Lekkie "curved" right arm will overcome the problem of the "unsymmetrical" system (the left on the set is straight). I used three gears 11-17-28, spaced all the way to the right, on my first BBS02 to ensure the chain wasn't over-stressed by needing to operate at an extreme angle (these three were all that was necessary with the motor). The "17" provided a straight chainline, so the other two gears were only one click "off".
 
I really appreciate all the responses. I've discounted the chain-too-short solution as the original front sprocket was 48 teeth, and the new Bafang one is 44 teeth.
However the right crankarm (and sprocket) is indeed displaced a few mm further out than on the BM (before Motor) bike, so I think that explains it. I can run just fine with just the gears 2-9, the lowest gears is not really necessary with the motor. Nice to have the low gear if I want to run without motor (or run out of battery). Will look in to the Lekkie chainring after biking season.
 
SdotC said:
I really appreciate all the responses. I've discounted the chain-too-short solution as the original front sprocket was 48 teeth, and the new Bafang one is 44 teeth.
However the right crankarm (and sprocket) is indeed displaced a few mm further out than on the BM (before Motor) bike, so I think that explains it. I can run just fine with just the gears 2-9, the lowest gears is not really necessary with the motor. Nice to have the low gear if I want to run without motor (or run out of battery). Will look in to the Lekkie chainring after biking season.

Ride around for a while to figure out which cog(s) you don't use. Then you could remove the cassette and move that/those cogs to the inside.
 
Back
Top