Originally Posted by
HillRider
However, that doesn't mean that a Campy shifter will work with a Shimano rear derailleur even if you use a Campy cassette and, in fact, it won't unless you use a converter such as a Jtek Shiftmate.
And this is because of the actuation ratio, I presume, as we discussed in another thread. The difference between Campy and Shimano is that Campy likes to randomly change the rear derailler actuation ratio whereas Shimano has always kept it the same (aside from a Dura Ace and possibly XTR exception here and there).