Derailier

[Gains84]

I almost changed my rear derailleur recently but as mentioned above, to be cheap changed the cable and outer housing first and that improved the performance incredibly so try that first id say - quite a therapeutic fettle too...in a way!

 

[Zee]

If that's the case then you can choose any 9/10 speed shimano or sram component

Before you go and pull the trigger on a SRAM derailleur, I should mention that Shimano STI shifters/Sram rear derailleurs and vice versa are not fully compatible.

Shimano road shift levers move the shift cable a greater length per shift (2:1) compared to SRAM road shifters (1:1)

2:1 = 2mm cable pull at the shifter results in 1mm movement at the rear derailleur
1:1 = 1mm cable pull per 1mm rear derailleur movement

so when pairing SRAM to Shimano, you will run into shifting issues on the rear, ie. you will have skipping and won't have all your gears..

I am not sure why the shop recommended you change just the rear derailleur to SRAM unless they were also insisting you change both shifters plus front and rear derailleurs. Best double check with the mechanic rather than the salesperson.

 

[Zakalwe]

Seeing as a derailleur doesn't have any set notches of movement and are essentially just a set of pulleys on a spring, I don't see how any discrepancy in shifter lever action would be incompatible with a derailleur provided the two extreme sides of movement are wide enough. Indexing is entirely managed by the shifters, derailleurs haven't changed changed since the days of down tube friction shifters. Try pulling the cable manually and you'll see. Shimano and SRAM use compatible cassettes and chains so are pretty interchangeable generally.

 

[cyberknight]

Seeing as a derailleur doesn't have any set notches of movement and are essentially just a set of pulleys on a spring, I don't see how any discrepancy in shifter lever action would be incompatible with a derailleur provided the two extreme sides of movement are wide enough. Indexing is entirely managed by the shifters, derailleurs haven't changed changed since the days of down tube friction shifters. Try pulling the cable manually and you'll see. Shimano and SRAM use compatible cassettes and chains so are pretty interchangeable generally.

See what Zee said above......
Although the deraillier is not indexed the amount of cable movement to produce the same amount of movement of the mech is different between sram and shimano and i assume campag as well.I do know that microshift parts are compatible as they operate the same ratios as shimano These differences are down to the way the mech is designed , even not getting the cable clamped on the right side of the bolt on the rear mech can induce poor shifting even using compatible shifters + mech.

 

[Zee]

Seeing as a derailleur doesn't have any set notches of movement and are essentially just a set of pulleys on a spring, I don't see how any discrepancy in shifter lever action would be incompatible with a derailleur provided the two extreme sides of movement are wide enough. Indexing is entirely managed by the shifters, derailleurs haven't changed changed since the days of down tube friction shifters. Try pulling the cable manually and you'll see. Shimano and SRAM use compatible cassettes and chains so are pretty interchangeable generally.

Thanks for chipping in Zakalwe. It seems illogical to me too but the fact of the matter is although they share the same basic construct, SRAM and Shimano rear derailleurs will move different distances across the cassette for a given amount of cable pull.

As such the different indexing of the shifters leading to the 2:1 and 1:1 cable movement at the shifter lever will cause mis-shifts when paired with the opposing make's rear derailleur. (front derailleurs are spared from this issue)

The compatibility of SRAM/Shimano cassette and chains stem from the identical standards of chain and drivetrain teeth width shared by the two systems rather than similarities between the shifting mechanisms.


edit. ta cyber, didn't see your reply there.

also, just to make things more confusing. If I recall correctly, the shimano's flatbar shifters for their hybrid groupsets do share the same 1:1 pull ratio so will be compatible with SRAM derailleurs- possibly what the bike shop guy had in mind.