Shimano GRX RD-RX827-SGS Di2 Wireless Rear Derailleur - 12-Speed Long Cage Shadow ES BLKShimano GRX RD RX827 SGS Di2 Wireless Rear Derailleur 12 Speed Long Cage Shadow ES Black. 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