RD-M9100 12 Speed Rear Derailleur The XTR M9100 series of derailleurs brings a new level of drivetrain silence thank to decreased tension in the low gear position and an added bumper on the pulley cage. Larger 13T pulleys increase efficiency and chain management while compatibility with SHIMANO's new 12-speed cassettes boosts range. Medium Cage: Enhance shifting performance -Optimized for new drive system Silent drivetrain -Decreased rear derailleur tension at low gear position, to prevent high chain tension at low gear -Add bumper at rear derailleur pulley cage for silent drive -Bigger 13T pulley Low profile design SHIMANO SHADOW RD+ For more aggressive riding -28 mm better ground clearance (vs. RD-M9100-SGS) Low sprocket combination -10-45T (12-speed) Long Cage: Enhance shifting performance -Optimized for new drive system Silent drivetrain -Decreased rear derailleur tension at low gear position, to prevent high chain tension at low gear -Add bumper at rear derailleur pulley cage -Bigger 13T pulley Low profile design -SHIMANO SHADOW RD+ Low sprocket combination -10-51T (12-speed) SKU: RD-M9100 ***These are OEM Shimano Parts, Brand new, Never Installed on Bike, Never used in any way, just NOT in the retail packaging.***