Originally Posted by
Ritterview
I'd like to believe this W2, but while a triple definitely is an indication for a longer cage length, so too is the size of the cassette.
Campy, however, which used to require a medium cage RD for its 13-29 cassette, has rigged its new 11-speed RD to be capable of handling cassettes all the way from 11-23 to 12-29.
That's why I said to look at the spec sheet. Maximum sprocket capacity on all Shimano road groups that have GS and SS versions is 27T although it can shift a larger sprocket on the road, minimum sprocket is 11T. The capacity change is in the maximum chainring difference with SS spec'ed at 16T and GS at 22T. Campy might be different.
All mountain groups that have a GS and SGS versions allow 34T max. 11T min. sprockets.
The difference is usually listed as total capacity which is the size difference between the largest and smallest chainrings, and the size difference between the largest and smallest sprockets on the cogset added together. Shimano lists total capacity as Road Short=29T, MTB Short (Medium)=33T, Road Long=37T, MTB long=43T, so as long as you don't exceed 14T difference in the crankset you can use the largest 10sp cogset Shimano makes with any size cage. if you go to a triple where typically Shimano supplies a 52-39-30 you have to switch to a GS because you have exceeded chainring capacity difference, the rear cluster capacity does not change.