The SLX M7100 series of derailleurs deliver advanced shifting performance with decreased tension in the low gear position and an added bumper on the pulley cage. Advanced shifting performance provides the confidence to enjoy any trailLow-profile designExtra wide range 12-speed drivetrain -10-51T (12-speed) -10-45T(12-speed)Decreased rear derailleur and chain tension in low gearNew bumper added to rear derailleur pulley cageBigger 13T pulleyShimano have pulled out all the stops to provide you with a derailleur that provides super smooth shifting performance that s fast and without any nasty shocks or noises. The larger 13T pulleys increase efficiency and chain management while compatibility with SHIMANO's new 12-speed cassettes boosts the range of gears you can now benefit from.