The new Shimano GRX 12-speed drivetrains are officially here. As gravel has evolved, so have the drivetrains and as a result, Shimano is offered three distinct options for the new GRX. You have the choice of a 1×12 with a 10-45t cassette, a 1×12 with a 10-51t cassette, or a 2×12 system with an 11-36t cassette.
I mostly use my gravel bikes for exploring and riding easy MTB trails, so I chose the 1×12 group with a 10-51t cassette for my build (Tyler chose the same). However, even gravel racers are starting to look to wide-range 1x drivetrains – just look at SBT GRVL which was won this year on a 1x drivetrain with a 10-52t cassette, and 52t chainring!
It’s notable here that this group uses the existing 12-speed MTB cassettes and chains for better cross-compatibility and fewer part numbers. Better still, the RX822 rear derailleur has the option to swap out the derailleur cage so you can run either 1x cassette option without having to buy an entirely new derailleur.
You also have the choice with the 1x group of choosing either a left brake lever-only, or a left brake lever with a ‘shifter’ that acts as a dropper post lever. I went with the dropper lever version as I wanted to see if you could run it both with, and without a dropper installed.
Finally, there are some Shimano PRO components to finish off the build.
Shimano RX820 Actual Weights
Starting with the shifters, it’s 296g for the right ST-RX820-R, and 274 for the left ST-RX820-LA . The non-dropper post version (ST-RX820-L) would likely be even lighter if you never plan to run a dropper. The brakes come disconnected and are both exactly 166g. The addition of the front mounting plate makes up for the extra housing length for the rear (1000mm vs 1700mm). And since this is not an electronic group, you’ll need some cables and housing. The shifter includes split housing and a cable that weighs in at 46g. For a lot of bikes, you’ll likely need an additional cable kit if your bike uses full housing.
Going along with the brakes, you’ll need some brake rotors. In this case, Shimano uses the same RT-MT800 rotor for Ultegra, GRX, and Deore XT. This one is a 160mm Centerlock rotor with Freeza tech which weighs 108g. Depending on your frame, you might need the SM-MA-R160D/D brake mount adapter which will add 17g. Included longer brake mount bolts are 14g, while the short ones are 7g.
Moving to the gearing, the rear derailleur for the 51t cassette checks in at 294g. The XT CX-M8100 10-51t cassette weighs 469g. The CN-M8100 12s chain is 283g for the 126L e-bike-rated version with the connecting link.
For the crankset, the RC-RX820-1-12 is a 1×12 crank with a 40t chainring (42t is also an option). This example is a 172.5mm length, and weighs in at 648g without a BB. Shimano still does not make a bottom bracket for BB386. Since I’m planning to build up the T-Lab X3-S I just reviewed, I needed to source my own. Fortunately, Enduro Bearing makes some of the best bottom brackets out there. So they sent over an XD-15p thread-together BB386 for the build that weighs 125g.
Shimano GRX Wheel Actual Weights
Shimano also has a new tubeless wheelset for GRX, mostly because of the new hub requirements. In order to use the exisitng MTB cassettes, the hub needs a Microspline freehub. So, the C32 WH-RX880 wheelset features hooked carbon rims with at 25.32mm internal width, 24 spokes, and sealed bearing hubs with a Microspline freehub. The rear checks in at 779g, while the front is 663 – both weights include tubeless rim tape and valve cores.
Shimano PRO Component Actual Weights
If you want to run a dropper and keep it all in the family, the Discover dropper post is available in a 27.2mm diameter with 70mm travel. The 414g dropper post includes cable and housing which adds another 83g uncut.
Finishing off the build from Shimano, the PRO Discover bar and stem along with an off-road saddle. The stem is an 80mm length with 6º rise with a weight of 160g. The 440mm aluminum bar with a 12º flare is 296g. Both have 31.8mm clamping diameter. The Stealth Off-Road saddle checks in at 202g.
For the complete tech overview on this group, read our launch coverage here.
