Shimano’s 2012 XTR Rear Derailler

Shimano’s 2012 XTR Rear Derailler Explained on how the system works and to get the low down on its “ON” and “OFF” switch,
The newest addition to the XTR Dyna Sys drivetrain is the RD M985 Shadow Plus rear derailleur. The Shadow Plus feature provides a selectable pivot for the pulley cage that can use a heavier spring and increased pivot friction to counteract the forces of up and down chain momentum in rough terrain.
The chain bouncing can often cause noise as the chain slaps the top and bottom of the chainstay, or even cause the chain to derail from the front ring in extreme circumstances.
The new pivot when selected to the ON position dampens the cage and consequent chain movement for a nearly silent and stable riding experience. In the OFF position the derailleur will function like a standard Shadow rear derailleur and eases the installation and removal of the rear wheel by relaxing the spring tension on the cage.


Shimano didn’t waste anytime updating both their XT and XTR groups. Reissued in 2010 with Dynasys and 2×10, IceTech and directional chains, both groups aren’t exactly aging. But, for 2012, both will see improvements.

XTR gets the new Shadow Plus rear derailleur, which claims to all but eliminate chain slap and dropped chains…which means a quieter, more flawless ride. XT gets a far more drastic update, adding a 2×10 option and borrowing a lot of the brake technology from XTR to virtually create a whole new group. In the video above, Shimano’s Bicycle Components Project Manager Matt Robertson runs through the changes.

Inside the new XTR Shadow Plus rear derailleur is a locking cam gear that holds the lower pulley cage in place. The effect is considerably more resistance to the cage pulling forward, even when pushing on it manually with more force than a bouncing suspension is likely to generate on bumpy trails or big drops. The gold switch should be turned downward (off) to remove the wheel and adjust the shifting, but for riding, it should remain on. As it rotates upward, a graduated cam pushes the silver band closed, clamping down on the ratchet gear and holding it in place.

The assembly adds a bit of weight, but nothing that trail/all-mountain riders should balk at for the potential gains in performance, quiet and keeping the chain where it’s supposed to be. I played around with it on the demo bikes and it does add some resistance to the downshift (thumb lever), but most people should acclimate to it quickly. It should be available in June.

2012 Shimano XTR rear derailleur details:

  • Uses Shimano’s new Shadow Plus technology
  • Weight: 210 grams
  • MSRP: $249.99
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