shimano xtr di2 rd-m9050 rear derailleur black, medium cage shimano on top of delivering smooth, effortless shifting in all conditions, shimano's xtr di2 rd-m9050 rear derailleur will make the aft-end of your drivetrain smarter than it's ever been before. with shimano's synchronized shift technology, the front and rear derailleurs operate in sync and have the ability to calculate your efficiency, thus the m9050 can automatically shuttle your chain from cog to cog to set you up with the best chain line for any given situation. this technology also protects the short cage derailleur, by making sure you never run out of chain when cross-gearing. moreover, shimano's e-tube system allows you to program your preferences beforehand, so your drivetrain is calibrated just the way you like it. of course, synchronized shift can be easily turned on and off as you please. the xtr di2 rd-m9050 rear derailleur is compatible with shimano's resilient and hassle-free e-tube wiring system.