Shimano Mountain Rear Derailleurs XT RD-M8120 Rear Derailleur

The last time we saw an update to Shimano’s workhorse XT group was back in 2015 when they made the switch to 11-speed. Fast forward four years and XT gets another refresh, so it comes as no surprise that Shimano’s new XT RD-M8120 Rear Derailleur makes the move to 12-speed, along with other refinements that improve shifting performance while bringing a new level of silence to your drivetrain.

These changes start with larger 13t pulleys that increase chain wrap, resulting in greater efficiency and better chain management. The XT derailleur is also quieter thanks to decreased tension in the low gears and an added bumper on the pulley cage that keeps things silent in rough terrain. Shimano also claims faster shifting and smoother transitions between gears, which is attributable in part to the Hyperglide+ technology of the cassette and chain, in addition to the larger pulleys. One thing that hasn’t changed is Shimano’s proven Shadow RD+ low-profile technology that keeps the derailleur tucked out of harm’s way when you’re riding through ankle-biting rocks that threaten to rip off your derailleur. It also retains the chain stabilizer switch that helps to eliminate chain slap and dropped chains by increasing spring tension. The switch can also be turned off which allows for easier wheel removal and installation.

The new XT 12-speed derailleur comes in two versions, the M8100 and M8120. This M8120 model is designed specifically for 2 x 12 gearing, to be paired up with Shimano’s new 10 – 45t cassette. It only works with the 10 – 45t cassette, though Shimano states it can be used with a single chainring up front if desired.

Shimano sticks with the old-reliable aluminum components in the XT derailleur. All of the linkage plates, knuckles, and cage sides are made from it, so while it may lack the carbon-fiber-laden aesthetic of the XTR line, it’s more affordable, and if you’re been running XT derailleurs as long as most of us around the office have, you know you’ll get plenty of mileage out of it.