Shimano's XTR Di2 RD-M9050 Rear Derailleur's coolest feature is definitely Shimano's Synchronized Shift system. You might think effortless, perfect-in-all-conditions shifting that's never compromised by wear and contamination would trump any entrant in this category, but, well, it doesn't. We even admit to being skeptical at first, since Synchronized Shift automatically shuttles your chain from cog to cog without any input from you, but the results of just one ride on this system speak for themselves. The RD-M9050 intelligently manages the fleet of cogs at the aft-end of your drivetrain.
By putting the rear and front derailleurs in communication with each other, Synchronized Shift can actually calculate your efficiency and perform simultaneous front and rear shifts to eliminate cross-chaining and set you up in the best chain line for any given gearing. These shifting patterns depends on the direction you're shifting and the combination you're shifting into, and they're also programmable via Shimano's E-Tube system, so you can set your preferences in advance to ensure that your internally-communicating drivetrain isn't conspiring against you.
Another category of big winners in the Synchronized Shift game are short cage derailleurs, which the system protects by making sure you never run out of chain when cross-gearing; it just adjusts the front and the rear to give you the gearing you want without tearing your derailleur off. Still, if you decide against Synchronized Shifting, then you can turn it on or off as your preference demands.
The shifting itself is peerless, as the derailleur always knows where it is, so its travel isn't restricted or lengthened by imperfect cables. It situates the chain squarely on every cog and it jumps between those positions with startling speed. No hesitation, no grinding. Ever.
As with other Shimano Di2 bits, the XTR rear derailleur is compatible with Shimano's rust-, stretch-, freeze-, and generally worry-free E-Tube wiring system. Its modularity makes it easy to set up on virtually any frame, though it does cohabitate with less friction when the frame is built with Di2 in mind.
- Synchronized Shift technology
- Shifting pattern can be programmed to your preferences
- E-Tube wiring system