I’ve just put some new wheels on my road bike.

The new wheels have a new cassette – I’ve gone from a 11-15 to a 12-26 cassette.

but the drivetrain sounds rough.

it sounds & turns fine when free wheeling.

it sounds rough from the rear mech.

is it just a matter of adjusting the rear mech?

Have you adjusted the rear mech?

Did you put a new chain on?

Is the chain the correct length, the old one would be too short going from 11-15 to 12-26 (think you mean 11-25?)

Can the RD cope with a 12-26t cassette?, a SS may be on the limit, a GS should be fine

Have you tried the Di2 trick of running the B screw the opposite way around?

nope not touched the mech.

no its the old chain

yep the old cassette was 11-25 the new 12-26

not sure its a sram red rear mech

not got a clue what you mean regarding b screw??

You really should put a new chain on with a new cassette as the old one will have worn for the old cassette.

Putting a new chain on will probably solve your problem.

The Di2 trick with the B screw is to allow Di2 RD’s to work with 11-28 cassettes, where you take the B screw and insert it the opposite way, effectivly giving a bigger range for the RD, I used this for a 9 speed Campagnolo RD which didn’t like a 12-27 cassette even though it was spec’d for it, works fine now.

You really should put a new chain on with a new cassette as the old one will have worn for the old cassette.

Not necessarilly in my experience, as long as the chain isn’t to worn. One of the chain checker thingys are useful in this respect, to gauage how worn your chain is.

It might be that the rear mech needs a little fettle – play around with it. And find out what the b tension screw does. 😀

cheers chaps – the chains not too old it isnt worn.

I’ll have a fiddle