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Swapping cassettes

JLIJLI Posts: 3
edited March 2009 in Workshop
I'm having a bit of bother with bigger hills in the Peak District and Pennines and I want to swap my 12-23 cassette for a 12-27. I've never done this before so I'd be very grateful for some advice. Do I need to get an 8 speed, like the existing cassette, and will I need a different chain (the bike is nearly new so the chain isn't at all worn).

Many thanks

John.

Posts

  • MonzaMonza Posts: 27
    Last week i had my first go at changing a rear cassette. I bought a chain-whip and lock ring removal tool from halfords for £14, and watched a vid on you tube. I cant post a link because i know nothing about computers but type in "how to change rear cassette" and bobs your uncle. The 8 speed cassette will match your 8 speed shifters.
  • nicklousenicklouse Posts: 81,520 Lives Here
    Good info on parktools linky in sig.

    the cassette needs to be the same spd and make, or have the same spline pattern. Shimano/sram use the same.
    as you want to fit a bigger cassette you will need a longer chain if you intend on using the big cogs together (not good to do)
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
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  • toslowtoslow Posts: 85
    you may need to check that your rear mech will be ok to accept a larger lower gear , as i always thought, wrongly or rightly that a short cage mech was not suitable for a 27 tooth bottom gear . anyhow you will need a new chain im afraid.
  • John.TJohn.T Posts: 3,698
    The short cage mech is fine with a 27 cog. You don't say if you have a double or a triple. If a double you will almost certainly need a new chain (unless you have a couple of spare links you can add). If a triple you will have a long cage road mech and may also have a long enough chain. Check on Parktools for how to set chain length and see if you have. If you have any doubts get a longer chain. It is far cheaper than getting your rear mech out of the back wheel after you forgot and hit big/big by mistake.
  • JLIJLI Posts: 3
    Many thanks everyone for your advice. I'll sort it out this weekend and see how much effect the change has in the Peaks next week.

    John.
  • An 8-speed cassette isn't availabe in 12-27. It is however available in 12-26. With a 52/42/30 triple this should get you up anything!
  • Chopping each cassette and rebuilding sprocket-by-sprocket to suit different rides FTW!

    Easy if you keep the same spacers.
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  • John.TJohn.T Posts: 3,698
    You can get 11/28 which will work on Shimano road mechs with a bit of care setting up. Several here.
    http://www.spacycles.co.uk/products.php?plid=m2b0s150p0
  • a_n_ta_n_t Posts: 2,011
    I went from 11-23 to 13-26 campag and didnt change the chain. works fine!
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  • RhodsRhods Posts: 400
    Not meaning to hijack, but a question along the same lines:

    If I were to have one wheel with a 12-25 and one with an 11-25, would it mean having to fiddle with the cable length from the shifters?

    Thanks
  • John.TJohn.T Posts: 3,698
    It should not. The most you should have to do is tweak the cable adjuster a little. I have 4 wheel sets and 2 bikes and swap them around with no adjustment needed.
  • itboffinitboffin Posts: 19,773
    It makes much more sense to change the last three sprocket block rather than a whole new cassette.
    Does anyone know if or where you can buy individual replacement sprockets for Shimano cassettes?
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  • alfabluealfablue Posts: 8,497
    itboffin wrote:
    It makes much more sense to change the last three sprocket block rather than a whole new cassette.
    Does anyone know if or where you can buy individual replacement sprockets for Shimano cassettes?
    I think St John Street Cycles sell them.
  • steve-msteve-m Posts: 106
    alfablue wrote:
    itboffin wrote:
    It makes much more sense to change the last three sprocket block rather than a whole new cassette.
    Does anyone know if or where you can buy individual replacement sprockets for Shimano cassettes?
    I think St John Street Cycles sell them.

    More an academic question since I have already ordered, but going from a 12-27 to 11-23 presumably it would be possible but a bit of a faff?
    Fixed, commute: Langster 08, FCN6
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  • John.TJohn.T Posts: 3,698
    If you are on Shimano 105 an up it is difficult to substitute any of the larger sprockets as they are on carriers and Shimano have carefully made things so it is almost impossible to do this. You would have to discard all the ones on the carrier and fit the ones you want from other suppliers.
    More an academic question since I have already ordered, but going from a 12-27 to 11-23 presumably it would be possible but a bit of a faff?
    If this is just a cassette change there is no problem at all. Going the other way may entail lengthening the chain slightly. It would depend on what method was used to set the length in the first place.
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