changing rear wheels

kerryman

hi folks,

this may be a silly question..... but....

If i change the rear wheel on my bike to a wheel with a different size cassette do i have to adjust the rear derailleur?

flasher

No, indexing would remain the same, but you could need to change the chain, chain length and rear derailleur depending on the cassette size you want to move to.

andy_wrx

How different in size ?

Where the cassette might mean you need to adjust the rear mech is in the B-tension screw, if you swap to a much bigger cassette and find that the mech cage is rubbing on the big cog.

You might have to fine-adjust the rear mech slightly so it engages the gears cleanly, and to adjust the top/bottom end-stops slightly, but that would be due to changing the wheel to one with slightly different dishing/axle adjustment rather than because of the different cassette.

You might be lucky and need no adjustment, I have two sets of wheels which I swap around between my best bike and TT bike and they need no adjustment.

You might need to adjust the chain length : if you were changing from say a 12-21 cassette to a 12-27, then you'll need a longer chain.
But say 12-23 to 12-25 or 12-25 to 12-27 you probably won't.

If you want to fit a really low MTB cassette, like a 11-32, onto a roadbike fitted with a short-cage rear mech, then you'll need a new rear mech.

John.T

I have my chains set for 12/27 and regularly swap wheels and cassettes with no trouble. Providing you have enough chain for the largest cog you will use then the rst look after themselves. It is a good idea to make sure all cassettes and chains are in similar condition or you will get accelerated wear. The only adjustment I make is to the 'B' screw when using 11/21 as I like to bring the jockey closer to the cassette. Not essential but it seems to make for a bit better change.