something not right after a cassette change

Adam0071 Posts: 31
edited January 2012 in Workshop
After my dearest wife bought me a new rear cassette for christmas I fitted it to find that the chain doesnt run smoothly when on the largest cog - I've changed from a 11-25 to 12-27 on a compact crankset. Is it that my chain needs changing for a longer/shorter one?? its fairly new as it is so didnt change it when I put the new cassette on. The gears shift smoothly up and down the cogs but the jockey wheel almost seems as though its resting on the cassette when its on the large cog - is it something basic that im just not familiar with being a beginner or is it a visit to the LBS??
Boardman Team Hard Tail
Specialized Allez


  • big_p
    big_p Posts: 565
    you need to screw in the b tension screw on the derailer, the top jocky wheel will be rolling along to top gear.
  • racingcondor
    racingcondor Posts: 1,434
    What are the two cassettes? If you moved from a SRAM 10 speed cassette to a Shimano one then you need to add the spacer behind the Shimano cassette otherwide it could just need a little bit of fettling per big p.
  • sungod
    sungod Posts: 16,873
    check the make/model of the rear mech, then look up the instructions to adjust it, it's straightforward to do...

    shimano, here...

    sram, here...,381
    my bike - faster than god's and twice as shiny
  • Thanks for the replies everyone - looks like its the B screw adjustment that is my problem then - as soon as I have some daylight I'll see what I can do with it. Thanks again.
    Boardman Team Hard Tail
    Specialized Allez