The Shimano RD-RX815 GRX rear derailleur is Shimano's first GRX Di2 rear derailleur. The 815 in the model name indicates that this is the short-cage version of the GRX rear derailleur. It utilizes an adjustable chain stabilizer to prevent chain slapping and drops.
Like other Shimano clutch derailleurs it has an ON/OFF switch that lets you switch the clutch on or off.
This rear derailleurs ensures silent and uninterrupted rear shifting on rough terrain, smooth and reliable mixed surface shifting.
It is compatible with any current road dual control lever and of course the GRX specific dual control levers.
Top sprocket: Max. 11T/Min. 11T
Low sprocket: Max. 42T/Min. 40T
Total capacity: 41T