Originally Posted by
Andrew R Stewart
BikePHL- (How i dislike having to title responses with some fake name...) Shimano will tell you that the max rear cog size for the Ultegra SL is 27T. A 28T will likely fit well enough. Not much more without comprimises of performance or chain wrap capicity. Andy.
That's correct which is why I qualified the Tiagra 12x30 recommendation. However, several posters have reported success with 30 and even 32T cogs with Ultegra rear derailleurs if the derailleur hanger geometry and b-screw cooperate. No guarantees, of course.