With an integrated chain stabilizer mechanism, the Shimano GRX derailleur provides a quieter experience along 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-RX815 Di2 version offers the digital precision of Shimano electronic shifting with synchronization and is compatible with road cassettes with a max cog size of 34T. - Adjustable, gravel-tuned chain stabilizer prevents chain slapping and drops - Switch stabilizer ON/OFF to match the terrain - Total capacity: 38T - Smooth and reliable mixed surface shifting - Compatible with current road Dual Control Lever - Maximum front difference: 17T - High cog: Max. 11T/Min. 11T - Low cog: Max. 34T/Min. 30T