With an integrated chain stabilizer mechanism, the Shimano GRX derailleur provides a quieter experience with shifting security and precision on mixed terrain. For rides on smooth surfaces, the derailleur features and ON/OFF switch for the chain stabilizer. The RD-RX817 Di2 version offers the digital precision of Shimano electronic shifting, as well as synchronized shifting and is compatible with MTB cassettes with a max cog size of 42T. - Adjustable, gravel-tuned chain stabilizer prevents chain slapping and drops - Switch stabilizer ON/OFF to match the terrain - Silent and uninterrupted rear shifting on rough terrain - Compatible with current road Dual Control Levers - High cog: Max. 11T/Min. 11T - Low cog: Max. 42T/Min. 40T - Total capacity: 31T