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Judicious dicking around with the b screw might save you but if not a short cage 10 speed SRAM mtb mech such as X9 will work. You'll need an inline barrel adjuster too.
The difference in chain between max max and min min determines the length of cage required but unless you have a bonkers large chain ring short cage should do 39/53 12/30.
Howard-
a short cage 10 speed SRAM mtb mech such as X9 will work
Official SRAM policy is to use the mid-cage for 2×10 with a big sprocket of 28-32, and long cage for 2×10 with a 36T sprocket.
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Judicious dicking around with the b screw might save you but if not a short cage 10 speed SRAM mtb mech such as X9 will work. You'll need an inline barrel adjuster too.
The difference in chain between max max and min min determines the length of cage required but unless you have a bonkers large chain ring short cage should do 39/53 12/30.>Just getting back to this, I have managed to get it working. 53/39 -> 12/30 on the back. Screwed the b screw all the way in to get clearance and it's shifting fine all the way through the gears. So, old 10 spd rival short cage can just work with a 12-30t cassette. sweet! until the sping snaps and derailleur explodes....
gbj_tester
TRA
Cleverly bought a bargain Ultegra 10spd cassette - 12-30T. Thought I could whack it on the bike without a compact chainset to give myself slightly better climbing gears. Turns out my old tech 10spd Rival derailleur wont get up to the 30T without interfering on the jockey wheel. Do I need WiFli or long cage rear mech? Any reason I couldn't use a MTB mech? Could also just bin the idea if it's more than £30.