The Shimano GRX RX827 Di2 Wireless rear derailleur paired with a 10-51t cassette (cassette sold separate) gives riders and racers the speed range and robustness to pursue any gravel challenge. With built-in automatic impact recovery an impact-deflecting shape and solid pulleys this derailleur stands up to hard impacts and still retains its lightning-quick shifting performance.Fully wireless shifting built for rough gravel terrainA wide link structure skid-plate design durable aluminum plate and solid pulley add robustness and longevityAutomatic Impact Recovery function instantly returns the derailleur to its original position after impactFeatures Shimano Shadow ES: A slimmer stronger evolution of Shimano's pioneering chain-stabilizing Shadow RD+ conceptTucked safely inside an enclosed space the battery won't budge even in rough terrain while remaining easily removable for charging