Upgrading the chainring, but what about the chain?

DonWerner

New Member
Hey guys,

I just bought a new chainring for my Bosch CX motor, an 18 teeth instead of the standard 15 teeth. Will I need to change lenght of the chain itself or will the new 18 teeth sprocket fit okay with the standard chain?
 

DrewSkates

New Member
I'm surprised no one has responded. How did the install of the 18T workout and did you have any issues to contend with. Really interested in finding out as I am now considering the same.
 

Chris Nolte

Well-Known Member
The chain might be okay without adding any length. Keep in mind that the Bosch system likes to spin fast and adding a larger chainring might not necessarily be the best for performance.
 

DrewSkates

New Member
Chris,
Thanks. The reason for the larger chairing is for speeds above 20 mph after the motor kicks off. I found the gears to be a bit limiting for powering down a flat at say 24+ mph trying to keep up with my son and also on long downhills. I would just use a smaller gear in the back under 20 mph while the motor is engaged. Any other concerns I should be aware of.
 

Chris Nolte

Well-Known Member
Chris,
Thanks. The reason for the larger chairing is for speeds above 20 mph after the motor kicks off. I found the gears to be a bit limiting for powering down a flat at say 24+ mph trying to keep up with my son and also on long downhills. I would just use a smaller gear in the back under 20 mph while the motor is engaged. Any other concerns I should be aware of.
The only concern is if you change the ratio to a ratio it could throw an error. It's not that likely, but it's possible. Bosch has a check to avoid users from tampering with the speed sensor.
 

DrewSkates

New Member
Chris,
Can you shed some light on the error and what would happen. I don't believe this would be tampering with the speed sensor as I am only changing the front sprocket from 15t to 17t or 18t. No other change.
 

Chris Nolte

Well-Known Member
It really shouldn't happen, but it could and if you see something like this it could be the culprit. It would only happen in the rare instance that your crank is moving at the same rpm as your wheel, but even then it's not guaranteed to happen.

I didn't mean to alarm you, I just wanted you to be aware of a potential challenge. As I mentioned you should be okay.
 

BurbManDan

Member
My Felt NINEe 20 came with a 15T chainring, which was replaced very early on with an 18T. I've had no issues from the sprocket, in over 30k miles. I do drop the chain off the front sprocket periodically - it's a bare chainring with no guide like you see on Haibikes and some others cranks, but I don't think this is related to the change in size. Definitely helps with higher gear ratios, though the increased size will produce higher torque loading on the motor drive side bearing, which is the primary weak spot of the Bosch motor design... However, my latest speed motor now has almost 13k miles on it (all with the 18T chainring), which is the highest mileage I've seen yet from any single motor. (hopefully I didn't just jinx it ;)