The Shimano GRX 11-speed rear derailleur provides silent and uninterrupted rear shifting on rough terrain. 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 ONOFF switch for the chain tensioner. The RD-RX812 rear derailleur is compatible with MTB cassettes with a 42T low sprocket max.