The Sora 9 speed STI levers on my road bike are borked but the rest of the kit is fine. So I have a plan.
Buy some new 10 spd 105 STIs, a 10 speed cassette and chain. My research tells me this is fine, the 9 speed tiagra rear mech has the same cable pull ratio as the 10 speed so it will work OK. Won't it?
I can't see any reason the 105 Double STI won't work with my Sora compact front mech.
So my issue is with the spare back wheel I use on the turbo trainer. It has a 9 speed cassette. I don't want to buy another 10 speed cassette just for the turbo. What will happen if I run the 10 spd set up with the 9 speed cassette? Obviously it won't shift properly but thats not really an issue on the turbo. Will any other mishaps befall me or my bike?