Cassette compatibility

[nammynake]

I'd like to fit a wider ratio cassette to replace my 9-speed Shimano HG-50 12-25 cassette, which is fitted to my Specialized Allez. I'd like a lower gear to help me on the Fred Whitton in May (I have a 50/34 compact chainset). Ideally I'd like it to be compatible with my current Sora dérailleur.

Can someone help explain what would be a straight swap. Would this 11-28 fit for instance?

http://www.chainreactioncycles.com/Models.aspx?Mod...

[Jimbo.]

I presume that if your bike has a Sora mech, then it's a Sora/Tiagra/non-series drivetrain, and therefore 9 speed. The cassette linked to is a 10 speed, therefore it won't be compatible with your bike in its current form. For it to work, you'd need new, 10 speed shifters (Shimano 105, Ultegra or Dura Ace): it's the shifters which govern everything.

For cassettes, you'll be wanting:

http://www.chainreactioncycles.com/Models.aspx?Mod... (Tiagra: nowt wrong with it)

...or...

http://www.chainreactioncycles.com/Models.aspx?Mod... (9 speed Ultegra).

And yes, should you go for one, it's a straight swap. You may have to adjust the chain length, which, if the lowest gear (biggest sprocket) is a lot bigger, may require a new chain. But with a new cassette, it's good practice anyway

[nammynake]

Thanks, you're right - the whole groupset is Sora, and therefore 9-speed. Cheers for the info.