Shimano STi compatibility

Timp2
Timp2 Posts: 2
edited October 2008 in Road beginners
I was woandering wheter a set of shimano 105 sti levers would be compatible with my tiagra 8 speed rear mech or would i also have to replace the rear mech, casette and wheel? I am currently using Sora levers
Thanks for any advice.
Tim

Comments

  • Harp
    Harp Posts: 79
    A rear mech isn't speed related, it works on a spring return. The indexed amount is done by the levers. I've used "9" speed rear mechs on a "10 " speed rear cassette.

    I don't think you could use 9 speed STI levers on an 8 speed cassette though as the indexing would be different. In saying that, I've used Ergo levers ( Campag ) on Shimano rear meach and cassette OK after being advised the indexing is different and it doesn't work.
  • andy_wrx
    andy_wrx Posts: 3,396
    As Harp says, the rear mech will be fine. The mechs don't 'know' how many speeds the you have. The shifters pull a certain amount of cable, the mech moves sideways that far. 9sp shifters pull slightly less cable per 'click' than 8sp shifters do, so the mech will happily move slightly less. 10sp shifters pull slightly less again.
    In fact, Tiagra is 9sp, so you're currently running a '9sp' rear mech ! This will work with 8sp, 9sp or 10sp systems.

    If you have a Sora 8sp system currently and want to go to 105 10sp shifters (or 10sp Ultegra or Dura Ace) or to older 9sp 105 (or 9sp Tiagra, or 2008 9sp Sora, or older 9sp Ultegra) then you'll need to change your 8sp cassette and chain.

    But the rear mech, front mech and chainset will be OK and you can fit 8/9/10sp cassettes on the wheel.

    Plus you'll need new bartape if you're changing shifters and you might as well fit new cables while you're at it.

    But the rear mech, front mech and chainset will be OK and you can fit 8/9/10sp cassettes on the wheel.

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