Does switching cassettes affect motor engagement?


New Member
I swapped out the SRAM PG-1230 Eagle (11-50, 12 speed) that came with my Powerfly 9.7 with an Eagle GX (10-50, 12 speed) and I notice some weird inconsistency with the motor, the top 5 gears of the GX are the same as the PG, -1 tooth per cog. However, it feels as if the motor doesn't quite know how to handle these gears: Assistance is not as smooth as it was with the original cassette and I also notice some weird intermittent vibration through the crank while in top gear.

Are the bosch units in these bikes SPECIFICALLY tuned to the gears that come with the bike and changing any of them throws the motor out of sync?

I have read in some forums that the motors have a specific wind per application and some people have experienced issues when tinkering with gears and such.

I have seen on the Trek site that the new Rail 9.9 has a rear cassette with the same gears as this Eagle GX I bought, (which makes me think there's no reason why I can't use similar hardware) but I wonder if the control unit and/or motor on the Rail is tuned specifically for that set up.

Is there an "ECU reflash" available? perhaps a Bosch technician can access the Purion unit and configure it to a new set of gears?

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New Member
Yes they can update the gearing in the firmware.

What about putting the original cassette back and swapping the front chainring/sprocket?

I've seen numerous vids/posts where people have swapped in larger/smaller chain rings depending on the riding environment.
It seems like a cheap and easy way to change your bike's transmission characteristics.


Same can take it to a dealer and they program the gearing in I believe. But you don't have to do any of that....I just don't know what the true effects are.