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Newbie question here.

Currently on my old Tiagra 4500, I have a Shimano HG50 9-speed Cassette, with 11-25T. I need another cassette, as I got a smart trainer, but it is a bit hard to find such a cassette. Can I use a CS-HG50 9S, but 12-25T cassette? What will be different?

1 Answer 1

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That will be fine.
The only difference is that you will lose ~9% from your top speed. Unless you are extremely powerful and wanting to sprint at the end of esports races you will never notice that loss of top speed.

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    Thanks! So I can replace it without changing the chain or other parts?
    – Dan Cantir
    Apr 20 at 12:14
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    You'll need a tool to tighten the lock ring. That can either be in the form of a dedicated tool or an adapter to use with a wrench.
    – Andy P
    Apr 20 at 12:21
  • The chain must accomodate both largest-largest as a maximum length, and smallest-smallest as a minimum length. your smallest-smallest - length increases (-> changes inside the previous lengths), so it can stay the same.
    – Burki
    Apr 20 at 18:39
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    @DanCantir People usually tell you it's a good idea to replace the chain when you're replacing the cassette. A worn chain might not mesh well with a new cassette. But if your chain is still pretty new (I have no idea if it is or not), you should be able to get away without it. Apr 20 at 21:57
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    @AndyP, OP will also need a chainwhip to tighten the lockring on the trainer because on a trainer the cassette will rotate clockwise freely. On a wheel the free-hub will keep that from happening.
    – Carel
    Apr 21 at 9:08

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