Rear derailleur compatibility

secretsam

I have an 11 speed 105 bike. 11-28 and short cage.
Considering wider cassette. I have a 9 speed Sora long cage mech. Will it talk to the shifters? I am under the impression that rear mechs are "stupid" and just do what they're told.

whyamihere

No, it won't work. Shifters and derailleurs need to have the same pull ratio, and those parts don't.

secretsam

whyamihere wrote:

No, it won't work. Shifters and derailleurs need to have the same pull ratio, and those parts don't.

Yeah, just seen a similar post on buying advice. Weird. I assumed rear mechs didn't "care"

photonic69

If you already have it then it will cost you nothing to try it. Go ahead and report back your findings.

whyamihere

SecretSam wrote:

whyamihere wrote:

No, it won't work. Shifters and derailleurs need to have the same pull ratio, and those parts don't.

Yeah, just seen a similar post on buying advice. Weird. I assumed rear mechs didn't "care"

That used to be true, within brands at least. Shimano 6, 7, 8, 9 and some 10 speed all used the same pull ratio. In that case, the mech didn't 'care', the number of gears you had was defined by the shifter and cassette/freewheel. Unfortunately, the manufacturers then started changing pull ratios and cross compatibility was lost.

davidof

SecretSam wrote:

I have an 11 speed 105 bike. 11-28 and short cage.
Considering wider cassette. I have a 9 speed Sora long cage mech. Will it talk to the shifters? I am under the impression that rear mechs are "stupid" and just do what they're told.

You could probably go x30 or even x32 on the top end with that setup.