Shimano's new M9000 XTR Rear Derailleur puts the components giant back on track in its never-ending battle with SRAM for drivetrain supremacy. Though years late to the one-by party (and, some would say, still not quite there), the new XTR derailleur is capable of handling cogs up to 40 teeth, while still allowing for a 10-tooth difference in front chainrings, should you choose to run them. Shimano altered the parallelogram of the derailleur a bit, and also moved the top pulley wheel to allow for greater capacity without resorting to bottoming out the B-screw. While it was at it, Shimano also decreased the profile of the derailleur cage by about 30mm to better keep rogue sticks and muck from getting to it. The clutch is now externally adjustable, too, so no more fiddling with that tiny wrench. While most of us will probably keep leaving it in the "on" position, the ultra-smooth shifts that accompany the "off" setting are tempting when the change is so quick.