Max cassette size?

ben@31
ben@31 Posts: 2,327
edited January 2015 in Workshop
Hello.
On one of my bikes I have a 12-25 Tiagra HG50 cassette. I'm thinking of replacing it with a cassette with a lower gear. I'm wondering how big a sprocket would work with the current rear derailleur? Would a 27T, 28T or 30T be compatable?

Thanks.
"The Prince of Wales is now the King of France" - Calton Kirby

Comments

  • arthur_scrimshaw
    arthur_scrimshaw Posts: 2,596
    What's the RD? On a standard 105 RD you can get away with a 30T but bear in mind your chain will almost certainly be too short if you fit this.
  • ben@31
    ben@31 Posts: 2,327
    Arthur Scrimshaw wrote:
    What's the RD?.

    9 speed Tiagra from 2011.
    "The Prince of Wales is now the King of France" - Calton Kirby
  • arthur_scrimshaw
    arthur_scrimshaw Posts: 2,596
    According to this the max is 27 which means you will get away with a 28 maybe a 30.

    http://www.chainreactioncycles.com/shim ... -prod19461
  • gozzy
    gozzy Posts: 640
    You can always screw the b-tension screw through from the other side to increase the clearance if it's tight on a larger cassette.
  • AntM
    AntM Posts: 10
    I switched from HG50 11-25 to Miche 12-30 with a short Tiagra RD on my old winter bike. There was loads of clearance between the top pulley and the 30 gear. I could have gotten away with a 32!
    It all really depends on the geometry of the rear hanger. It won't work on all bikes. Just don't ride in big-big gear! as you might not have enough chain lenth.

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