The new RX800/805 rear derailleurs have many features in common with their "siblings", the ULTEGRA R8000/R8050 rear derailleurs, including the same high level of precision or the SHIMANO SHADOW RD rear derailleur design.
However, the new RX800/805 rear derailleurs are now equipped with the stabiliser mechanism (SHIMANO SHADOW RD+), which stabilises the chain especially on rough, uneven surfaces. As with the SHIMANO mountain bike rear derailleurs, the switch for this SHADOW RD+ friction damper is located on the top of the rear derailleur body. In the "On" position, the forward and backward movement of the rear derailleur cage is extremely slowed down, which reduces the impact of the chain (and thus the risk of jumping off and shifting) as well as the development of noise.
The RX800/805 rear derailleurs are compatible with SHIMANO's dual control shift/brake levers (Di2 or mechanical) and can be used as the largest pinion for cassettes with 28 to 34 teeth. This makes these rear derailleurs the ideal complement for racing bikes intended for off-road or adventure use, including bikes with cyclocross or compact ratios from 46-36Z to 50-34Z cranks