The top of the line SRAM XX1 Type 2.1 rear derailleur features small improvements over the previous model, to give you smooth, precise shifting and ultra-reliable performance with your SRAM 1x11 drivetrain. With its "horizontal parallelogram" design and pulley offset, the SRAM XX1 Type 2.1 11-speed Rear Derailleur keeps the chain gap constant across all 11 gears, providing fast, precise shifts. By limiting all movement to the horizontal axis, this design is faster, reduces shift force and eliminates ghost shifting. Roller Bearing Clutch technology reduces bounce and chain slap, while Cage Lock technology makes wheel removal and installation easier than ever before. Paired with the XX1 shifter, the X-Horizon rear derailleur forms the backbone of X-Actuation technology for unbelievably smooth shifting action.