Shimano GRX Drivetrain: Gravel From The Get Go

A ground-up design for the new world of riding

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And to think if we’d only waited three years we could’ve shown up at Dirty Kanza aboard a gravel bike spec’d with a Shimano derived  Di2 1x drivetrain. It was after all back in 2016 when we built a project bike to ride at DK that used a variety of pirated parts including a Shimano Ultegra crank with a WolfTooth Drop Stop chairing mated to a mountain bike derived XTR rear derailleur to get the needed 11-42 gear spread. Ah, those were the days!

But no longer is there a need to look in the rear view mirror. Today marks the beginning of a long-awaited love affair between gravel riding and those with a predilection to using Shimano components. Shimano is launching what they’re calling “the world’s first gravel specific component group.” Though late to officially jump into the dual-sport world, in typical Shimano character, the gravel specific group was years in the R&D process prior to launch. From Almanzo in Minnesota to Dirty Kanza to the Rock Cobbler in California, we’ve seen Shimano techs and ambassadors at several gravel events.

Shimano’s road product manager Dave Lawrence said when they first caught wind of the 2014 Almanzo ride getting over 700 riders showing-up all based on social media, the product group were forced to ask themselves, “How does that happen?!” And so the investigatory process began.  Two years later Shimano took a deep dive with field testing in Kansas with former DK200 winner Dan Hughes. With Japanese and European techs in tow, Shimano was intent on finding out how to translate their gravel findings with other users and markets.

As big of news as the introduction of this ground-up, gravel specific Shimano GRX group is, there are some who will simply rejoice that Shimano is finally offering an official 1x gravel specific drivetrain. And still, there will be others who lament that it’s not a 12-speed system.

To this last point, as Shimano road brand manager Nick Legan offers, “We still think there’s a lot of skin on the 11-speed bones. We’re always working on new things and you can probably guess that if 12-speed comes it will be with Dura-Ace. Our goal with GRX was to not only design components that reflect the variety of gravel riding that’s out there, but important too was to make sure there was a high-degree of upgrade compatibility with what people are already using.”

Shimano 1x GRX drivetrain.

“Over the last few years we have realized that there is a new level of diversity in road riding which was more than just an extension of road riding and that it required its own family of products. Things are changing in the drop bar world, and the experience that people are looking for is different.”

THE CRUX OF IT ALL

The quick and dirty is that Shimano’s GRX gruppo is comprised of both a 1x (RX810-1) and 2x (RX810-2) drivetrain in your choice of either mechanical and electronic guise.  Up front the aluminum crank uses either a 1x has chainring sized in either a 40 or 42t configuration with the 2x offering a choice between a 48/31 or 46/30 combo. Actually, Shimano’s GRX gravel hug even extended to cyclists with 10-speed drivetrains.

The 17 tooth delta found with the 48/31 combo is the largest ever used by Shimano and they say that it’s intended to embrace the wide diversity of dual-purpose riding. As Legan (a veteran of Dirty Kanza, Trans Iowa, Gravel Worlds, Tour Divide and the author of “Gravel Cycling” ) explained, “When people say they’re riding gravel, that can mean something completely different from California to Kansas to New England and that’s the rider this group is intended for!”

2x  46-30 GRX chainrings and crank

Both cranks are offered in 170, 172.5, and 175mm lengths and both can be converted from a single chainring to a double arrangement. To better accommodate wider tires for gravel riding, the chainline has been pushed out 2.5mm which necessitates a GRX front derailleur with the 2x crank.

The 1x chainring teeth mimic those used on the mountain bike parts and feature a wider and taller profile.

In the rear Shimano is using either an 11-40 or 11-42 cassette for the 1x and 11-34 for the 2x. If there is a bias to be found in the available gear inches, it’s definitely to the side of climbing versus top gear speed sessions. As Legan added, “I know for many gravel riders a 1:1 ratio is not low enough for certain situations. Our goal with GRX  was to create a gear range that would encourage you to stay in the saddle.  Bike shops will appreciate the lack of new part numbers as the GRX cassettes and chains are all compatible with previous parts.

GETTING LEVER’D

The Di2 (ST-RX815) levers receive an 18mm higher brake axis which provides a bit more leverage. The lever blade itself is curved slightly making it easier for your fingers to access, and the hoods and the brake lever blades get a textured surface to prevent hands from slipping as well as an increased hood perch to better secure your hands in the hoods.

The 1×11 mechanical options in the GRX range created an opportunity to provide a specific lever that foregoes any shifter elements. Additionally, GRX features a left-side lever designed to actuate a (gasp!) dropper post.

For Di2 there will not be a dedicated 1x left lever, but they will feature additional buttons which can be programmed as shifters or to flip through the pages on your paired cycling computer

One of the more surprising elements of the GRX line-up is the addition of new “sub-levers” which is a left/right side,  inline ever that clamps to the tops/flats of the handlebar for an added braking position.

THE REAR MECH

Between the mechanical (RD-RX810) and electronic (RD-RX815) drivetrains there are four different derailleurs to accommodate the different gear spreads.

LEST WE ROLL

Along with all the drivetrain parts Shimano is also rolling out a new gravel intended wheelset available in both 700c and 650b sizes. The aluminum wheels use 12mm thru-axles, have a nice wide 21.6 internal width and are tubeless ready. Best of all, they will sell for $419.99.

If all goes to plan, we were told that a dozen or so GRX spec’d bikes will be competing at the upcoming Dirty Kanza, most likely underneath some previous event winners.

For more info on Shimano GRX

 

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