Quote Originally Posted by DebW View Post
Is your crankset double or triple, and how many teeth in each ring? A RD has a maximum cassette cog it can handle as well as a maximum tooth difference (add differences in cassette large-small and chainring large-small). Tooth difference defines the amount of chain that the RD can wrap up.
It's a compact 50/34. Yes, I was basically told the same thing by a LBS...that my current 6600 SL RD is maxed out with my current 12-25 cassette...so it would not be able to accommodate a 27t or 28t cog. However...when I do the formula you provided above, I get a maximum difference of 29...so now I'm confused...