SRAM's X1 group harnesses all of the groundbreaking technological and design features of the more expensive XX1 and X01 groupsets, but renders it without the more expensive materials to keep cost down a bit. The SRAM X1 Type 2. 1 Rear Derailleur takes the original design and makes some tiny improvements to elements like the bearings and the clutch mechanism to ensure better performance and longevity. As mentioned, the X1 11 Speed Rear Derailleur packs in all of SRAM's top one by engineering to ensure rear shifts are smooth, accurate, and predictable. Starting with the offset pulleys, the tall square toothed X Sync profiles work to positively engage and manage the chain better than traditional pulleys. These pulleys work in conjunction with the X HORIZON's straight parallelogram design, which limits all movement to the horizontal axis, thus eliminating ghost shifting and reducing shifting force. SRAM's proven Roller Bearing Clutch is also present, which delivers maximum drivetrain stability by maintaining consistent tension on the chain even while riding in the most demanding conditions. Finishing off the rear mechanism are sealed cartridge bearings and SRAM's handy Cage Lock design that keeps the derailleur locked out of the way for easy rear wheel installationremoval. SRAM's X1 Type 2. 1 Rear Derailleur is available in one color and is only compatible with SRAM 11 speed XX1, X01, or X1 drivetrains.