You may have answered this question previously, but I cannot seem to find the right archive, so here I go again: Shimano has recently come out with a 10-speed off-road group. Previous generations of rear derailleurs used to be backwards compatible with 9- and even 8-speed and worked with STI shifters too, for ‘cross use. Is that still the situation or have they changed the cable pull ratio?
To pass the wintertime blues, I started messing around with a newish XTR rear derailleur with the intention of converting it to a short cage. I made the rounds to a couple of knowledgeable shops in my town and they could not give me a firm answer as to whether I can do so or not.
With the advent of its 10-speed MTB drivetrain, Shimano has changed the cable pull ratio, and it is no longer cross compatible with previous generations of Shimano MTB or road drivetrains. I actually have discussed this here: http://singletrack./tech-faq-what-about-1×9-or-10.