Shimano FD-RX815 GRX Di2 Front Derailleur
Gravel bikes are here to stay, and anyone who says otherwise has Shimano to answer to. The Shimano GRX gravel bike groupset adapts typical Shimano road technologies to mixed-terrain use. One of the most important components of any road adoption to gravel is the inclusion of a wide gear range. The Shimano GRX RD-RX815 Di2 Rear Derailleur and RD-RX817 Di2 rear derailleur takes care of that and then some.
Simply put, the Shimano GRX RD-RX815 Di2 rear derailleur is a combination of the Shimano Ultegra RX rear derailleur and a Shimano mountain bike rear derailleur. It features a slim Shadow profile and clutch mechanism but has a slightly stronger clutch compared to Ultegra RX. It is also very slightly heavier than Ultegra RX, but the overall quality matches that of Shimano Ultegra. The Shimano GRX RD-RX812 rear derailleur is 1x-specific
The Shimano GRX RD-RX815 Di2 rear derailleur for electronic shifting is optimized for Shimano 2 x 11 drivetrains, though it can also be used with narrow-range 1x11 Shimano drivetrains as well. It is compatible with all Shimano Ultegra R8000 Di2 and Dura-Ace R9100 Di2 shifters.
For wide-range 1 x 11 Shimano gravel drivetrains, Shimano recommends the Shimano GRX RD-RX817 Di2 Rear Derailleur, which can easily run an 11-42t cassette option.