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changing rear wheels

kerrymankerryman Posts: 33
edited March 2009 in Road beginners
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?


  • flasherflasher Posts: 1,734
    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_wrxandy_wrx Posts: 3,396
    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.TJohn.T Posts: 3,698
    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.
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