Help Needed: Change of cassette from 12/25 to 11/28

Baybash
Baybash Posts: 136
edited September 2009 in Road beginners
I've been given a new cassette for my road bike. I have Shimano Sora 8 speed and the old cassette was a 12/25 and I now have a Shimano HG70 11/28. Can I just swap the cassettes?
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Comments

  • redddraggon
    redddraggon Posts: 10,862
    Depends on your chainlength. If the length is right it'll work.

    With the same length chain + medium cage mech I've successfully used all combinations of triple, compact and double, with 12-25 and 13-29 with all gears useable.
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  • Baybash
    Baybash Posts: 136
    What chain length should I have then?
    exercise.png
  • skyd0g
    skyd0g Posts: 2,540
    Cycling weakly
  • bigjim
    bigjim Posts: 780
    Fit it and try it. I doubt you will need to change the chain length. It's not a big jump.
  • redddraggon
    redddraggon Posts: 10,862
    Baybash wrote:
    What chain length should I have then?

    Depends on your chainstay length and stuff.
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  • I change my casstte between the sizes you have frequently and on different bikes. Never had any problems. There should be enough slack in the chain to cope with the 12-28. As the other person say just try it and see if you can get into the 39/28 gear
  • Baytt
    Baytt Posts: 102
    if you have a long cage mech, it should be able to handle it.
  • John.T
    John.T Posts: 3,698
    morrisje wrote:
    I change my casstte between the sizes you have frequently and on different bikes. Never had any problems. There should be enough slack in the chain to cope with the 12-28. As the other person say just try it and see if you can get into the 39/28 gear
    You need to be able to get into the big ring and 28 sprocket safely. If you can then no problem. You should not be using this one (much) but you will hit it one day. If the chain is too short and it can not go into it then the mech will go into the spokes.
  • bigjim
    bigjim Posts: 780
    Why would you go big ring and 28 sprocket?
  • John.T
    John.T Posts: 3,698
    You need to be able to use it safely because you will one day hit it by accident and it can be a long walk home. You would not normally use it. No go areas on a bike are not helpful.
  • turnerjohn
    turnerjohn Posts: 1,069
    er one thing no thing no one asked but are both the cassettes the same number of cogs? ie; 8 ! if not you got a prob ! if they are your be fine ! :-)
  • John.T
    John.T Posts: 3,698
    Baybash wrote:
    What chain length should I have then?
    Put the bike in big ring and small sprocket. The jockey wheels should line up vertically. There is a bit of tolerance either way but better with the lower one slightly behind the top one.
  • An 8 speed 11-28 (11,12,14,16,18,21,24,28) is a poor choice for a road cassette as the jumps between some gears such as 12 to 14, 14 to 16, 18 to 21, 21 to 24, and 24 to 28 are too big. In fact, only 11 to 12 and 16 to 18 are what i would consider acceptable.

    With 8 speed road cassettes it's best to stick to something like 12-25, 12-26, 13-26, or 12-23, 13-23 if you don't need a 25 or 26.