With an integrated chain stabilizer mechanism, the SHIMANO GRX derailleur provides a quieter experience and shifting security and precision on mixed terrain. For rides on smooth surfaces, the derailleur features an ON/OFF switch for the chain tensioner. Its compatible with current road dual control lever and gives you precise shifting every time. Shimano Grx RD-RX812 11 Speed Derailleur Features Adjustable chain stabilizer prevents chain slapping & drops Smooth and reliable mixed surface shifting Compatible with current road dual control lever Top sprocket: Max. 11T/Min. 11T Low sprocket: Max. 42T/Min. 40T Total capacity: 31T