Piecing together a 1x Di2 gravel drivetrain from individual boxes means matching GRX shifters, the right Di2 wiring, and a rear derailleur to whatever cassette you land on — and hoping the cage length and capacity actually line up. Shimano's GRX Di2 1x 11-Speed Kit takes the guesswork out of that by bundling the shift, brake, and rear-shifting hardware around a wide-range 1x cassette. The 1x-specific derailleur and cassette are already matched, so the range decision is made and the parts talk to each other out of the box.

The heart of the kit is the RD-RX817 rear derailleur, Shimano's 1x-only Di2 unit. The RD-RX817 rear derailleur is the 1x-specific Di2 unit with a longer cage designed for mountain bike cassettes up to 42 teeth. Shadow RD+ geometry tucks the derailleur close to the frame for protection and ground clearance, while the adjustable clutch tensioner keeps chain tension consistent over rough terrain. The clutch is tuned for gravel conditions and includes an on/off switch for easier wheel removal, and with 31 teeth of total capacity, the derailleur handles the jump from an 11-tooth small cog to 40 or 42 teeth without issue. One thing worth knowing before you build: the RD-RX817 was developed by Shimano specifically for use in 1x bikes, which means running this rear derailleur with a front derailleur is officially not supported. If you ever think you'll want a front shifter down the road, this isn't the derailleur for that plan.

For the cassette, this kit is built around wide-range 1x gearing. It includes an 11-42T SLX CS-M7000 cassette, which steps through 11-13-15-17-19-21-24-28-32-37-42 teeth, using steel cogs through 37 teeth with an aluminum 42-tooth climbing cog mounted on an aluminum spider that keeps weight reasonable while maintaining stiffness. The cassette fits standard HG11 freehub bodies, including road freehubs with the included spacer. That 11-42T spread gives you a low gear for loaded climbs and a tight enough top end for paved connectors between dirt sectors.... Read More