Originally Posted by
cpsqlrwn
I posted this in the Mechanics Forum, but I thought I might get more response here. My apologies for it not really being C&V.
I am about to install an Ultra Drive 10-speed 12-30 rear cassette onto one of my bikes and I am contemplating the use of a Campy 10-speed medium cage rear derailleur. This would be the derailleur that came out when Campy came out with the first 10-speed 13-29 cassettes. The documentation on this derailleur indicates the max cog is 29, but I'm thinking that may be because Campy's max cog at the time was 29. In any case, I am interested in knowing if anyone out there has used this derailleur with a 12-30 and if it handles that cassette acceptably. Or must I go with a long cage dereailleur. This bike will be for mountain riding so I am sure the large cog will be used occassionally. Would the concern with this setup be adequate chain wrap or would the concern be pulley clearance from the cassette or are both of these things issues? Thanks very much for any assistance!
First, Campy's recommendation before the 12/30 was to use the medium cage derailleur with a compact and the 13/29, and to use the long-cage for a triple with 13-29. I have a 13/39 with triple on one bike, and the long cage. If I am not careful with chain length (number of links), I can get interference between the jockey wheel and the large rear sprocket. I would take Campy's recommendations as they state them, unless I have time and $$ for a lot of experimenting. Shimano is said to have margin in their specs, but I'm not sure if it's true for Campy.
Second, the 12-30 has a spread of 18 teeth, where the 13-29 has a spread of 16 teeth and a larger large sprocket. That might have been enough for Campy to alter the rear mech geometry, unless the cassette is intended for compacts.
I really don't have experience with making a 12-30 work. But I do have a lot of Campy experience, and I would go with their guidelines.