Has anyone added a front derailleur to a Bosch?

[Jeff Backes]

I've seen three or four difference cog sizes for the front of the mid drive. Most bikes use a front derailleur to switch between cogs.

Has anyone ever hacked a Bosch mid-drive to have multiple front cogs and a front derailleur?

Just off the top of my head, there is probably not enough difference between sizes, but I just love to do things the wrong way (and pay too much for it).

jeff

 

[Jeff Backes]

I did some math on the setup. There is lots of overlap with the smallest and largest sprockets readily available sizes. Still might be a fun hack. With new digital shifting solutions that move the front derailleur for you, it give some extra speed at one end and lots of climb at the other with LOTS of fine control. If my math is right that's 8 overdrive gears instead of two!

Below's list has two sprockets A = 14, B = 22

jeff

0.3889    A
0.4375    A
0.5000    A
0.5833    A
0.6111    B
0.6667    A
0.6875    B
0.7368    A
0.7857    B
0.8235    A
0.9167    B
0.9333    A
1.0476    B
1.0769    A
1.1579    B
1.2727    A
1.2941    B
1.4667    B
1.6923    B
2.0000    B

 

[pxpaulx]

Since they run 10-11 speed rear gearing, there really isn't a need to do this. The reason for the small cogs is that the bosch motor runs at something like a 3:1 gear ratio, vs a standard front drive train (yamaha and brose are both 1:1, which is why those can use a dual chainring up front). Because the difference would be so small, and the motor can't really handle much larger chain rings, it wouldn't really work, and the motor isn't designed for it.

 

[Chris Nolte]

I agree with Paul. It's not designed for it so it would be quite difficult to make it work. I would focus more on the gearing in the rear and if you need to you can swap the front sprocket.

 

[EddieJ]

The ratio is 2.5

You can buy a dual front sprocket kit, which has to be changed across manually.

By memory the ratio is 15t and 18t. 15t for off road use and 18t for on road use.