Changing cassette - re-index gears?

TKF
TKF Posts: 279
edited September 2013 in Workshop
I have a new cassette and chain arriving in the post tomorrow. Will I need to reindex the gears?

The only thing changing over the outgoing cassette is the number of teeth. Going from 12-25 to 11-28.

I'm assuming that there will be no need to change anything?

Comments

  • Mad_Malx
    Mad_Malx Posts: 5,183
    Probably not, but if you can change a cassette I'm sure you can manage indexing.
  • Crank spank
    Crank spank Posts: 11
    You will need to increase your gear cable tension to allow for the greater step up of the new cassette. Very easy to do.
  • Barbarossa
    Barbarossa Posts: 248
    ^??
  • Crank spank
    Crank spank Posts: 11
    The new cassette has a different ratio which will require slightly more cable tension. Hope that's clearer, don't know how else to say it.
  • Mad_Malx
    Mad_Malx Posts: 5,183
    Don't think tension will change. The cogs are in the same position horizontally. May want to adjust 'b' screw, but it'll probably be fine.
  • rolf_f
    rolf_f Posts: 16,015
    Mad_Malx wrote:
    Don't think tension will change. The cogs are in the same position horizontally. May want to adjust 'b' screw, but it'll probably be fine.

    That's the only thing I can think of. I never change the cable tension going from 25s to 27s and 29s and can't see why it would be necessary - not only are the cogs in the same position, more importantly so is the rear mech!

    Anyway, to check b screw, stick the bike in the largest sprocket and see how the chain runs from the sprocket to the upper jockey wheel of the derailleur. If the cage is too close to the sprocket it will not run smoothly between the two. The b screw allows you to move the cage away from the cassette.
    Faster than a tent.......
  • majormantra
    majormantra Posts: 2,094
    Crank spank wrote:
    The new cassette has a different ratio which will require slightly more cable tension. Hope that's clearer, don't know how else to say it.

    If you're going to post mechanical advice, try not to make it totally wrong.

    As above, you might need to adjust the B screw but otherwise, as long as you include the correct spacers (if any) the cassette will be in the same position.
  • TKF
    TKF Posts: 279
    Rolf F wrote:
    Anyway, to check b screw, stick the bike in the largest sprocket and see how the chain runs from the sprocket to the upper jockey wheel of the derailleur. If the cage is too close to the sprocket it will not run smoothly between the two. The b screw allows you to move the cage away from the cassette.
    Good tip thanks.
  • rolf_f
    rolf_f Posts: 16,015
    TKF wrote:
    Rolf F wrote:
    Anyway, to check b screw, stick the bike in the largest sprocket and see how the chain runs from the sprocket to the upper jockey wheel of the derailleur. If the cage is too close to the sprocket it will not run smoothly between the two. The b screw allows you to move the cage away from the cassette.
    Good tip thanks.

    So good I should remember to follow it myself when I change cassettes! :oops:
    Faster than a tent.......
  • keef66
    keef66 Posts: 13,123
    Crank spank wrote:
    The new cassette has a different ratio which will require slightly more cable tension. Hope that's clearer, don't know how else to say it.

    -1. Whatever you do, don't do this. Cable tension and sprocket size are completely unrelated.

    You will need to make your new chain a bit longer than the old one was to cater for the larger sprocket, and as has already been mentioned you may need to adjust the B screw for the same reason. Indexing should remain exactly the same though.
  • TKF
    TKF Posts: 279
    keef66 wrote:
    You will need to make your new chain a bit longer than the old one was to cater for the larger sprocket
    Do I definitely need to do this?

    And if so can I fit the quick link from a KMC?

    The chain is 6701 (116 links) and cassette is 6700.
  • keef66
    keef66 Posts: 13,123
    Going from a 25t biggest sprocket to a 28t you'd ideally need a slightly longer chain, possibly just one link (inner plus outer)

    This is assuming your old chain was the optimum length for the old setup.

    All I really meant was don't just automatically cut the new chain to the same length as the old one.

    Using a KMC link is fine. In fact it's preferable in terms of convenience than joining it using the Shimano snap-off pin.
  • TKF
    TKF Posts: 279
    How does this look? Worth adjusting further away?

    It seems to run fairly smoothly pedalling by hand.

    4798c357a65e8d39859c78cf0fcf94c0.jpg
  • rolf_f
    rolf_f Posts: 16,015
    TKF wrote:
    How does this look? Worth adjusting further away?

    A little too far already I'd say - you want it as close as possible for the best shifting - but not so close that the chain can't run smoothly. A case of trial and error to get the best balance.
    Faster than a tent.......

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