Shimano Releases New 2x12 GRX Di2 Drivetrain

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Today, Shimano announced its new electronic 2x12 gravel drivetrain, GRX RX825 Di2. Rather than overhauling the system, Shimano has brought updated tech from its electronic road groups over to its 2x12 gravel-specific platform. The announcement came just in time for next weekend’s Unbound Gravel, which has morphed into one of the best-attended bike races in the country, so there’s a good chance you’ll see a few Shimano-sponsored pros in the field on brand new off-road Di2. I got a chance to preview the new group at Stetina’s Paydirt in Carson City, NV, last week, so here’s an intro to GRX Di2, as well as my first impressions.

Electrified Gravel

Shimano first introduced GRX in 2019 with 1x11, 2x10, and 2x11 options, and electronic Di2 11-speed. While GRX mechanical was updated to 12-speed last summer, we’ve been waiting to see what that meant for the battery-powered version of the group.

Photo: Cy Whitling

What about GRX is gravel specific? It has easier gearing for more interesting terrain, a derailleur with a clutch mechanism (Shimano’s is called SHADOW RD+) for less chain slap, ergonomic, textured brake hoods and friction-coated brake levers for better control and comfort, and a wider chainline for more tire clearance. I’ve spent half a year on the mechanical wide-range GRX drivetrain and find it to be utterly appealing.

This launch also includes "GRX" pedals. They're rebranded XTs, which are a go-to for many mountain and gravel riders for a reason. Photo: Kevin Fickling / Shimano

The new GRX Di2 group combines those features with the upgrades that Shimano has rolled out on the road side over the past couple of years. While the derailleurs are still wired to a battery installed inside the frame, the cockpit is now wireless. The rear derailleur does all the “thinking” for the system and is where the charging port is located. The shifting modes and layout are ultra-programmable via the E-Tube Project Cyclist app.

Pricing and Weight

The whole groupset retails for around $2,535, almost a grand more than the mechanical 2x12 version, which costs $1,585, but nearly the same price as the prior generation of GRX Di2.

GRX Di2 mounted to my Canyon Grizl (review coming soon). Photo: Kevin Fickling / Shimano

Shimano says the group as a whole is a touch lighter (2,925.5 g) than mechanical 2x GRX (2961.5 g). The electronic rear derailleur gains 40 g, the front derailleur gains another 47 g, and the battery itself weighs a claimed 53 grams. However, the Di2 brake/shifter assemblies are about 90 g lighter each, and if you want to get pedantic, cable and housing weighs about 120 g for each derailleur, while Di2’s wires are only 7.25 grams.

In total, you're not making significant weight gains or loses when moving to Di2. That’s generally the case with Shimano’s electronic systems on the road side too – the choice between Di2 and mechanical shifting should be motivated by performance concerns, not weight.

Gearing Options

As with the mechanical 2x12 GRX components, Di2 is available with a 48/31T up front, or 46/30 if you opt for the more affordable 600-series crankset. The GRX cassette is either 11-36T or 11-34T and only works on an HG L2 freehub body, not the MS freehub body Shimano's 1x systems mate to.

The brain of the entire system lives in this rear derailleur. Photo: Kevin Fickling / Shimano

This product update shows Shimano’s continued commitment to the front derailleur even as other brands have moved away from it – apparently, around one-third of aftermarket mechanical GRX sales in North America are 2x12 (and that percentage is even higher in Europe). Based on what I heard when I was infiltrating a media camp full of roadies, there’s still plenty of demand for big gears. The other editors in attendance were bummed that the GRX front derailleur tops out at 48T and the rear cassette’s hardest gear is only an 11T rather than a 10T, and that the crank isn’t offered with a power meter. However, it is possible to run a bigger road crankset like Ultegra, as long as you pair it with its corresponding road front derailleur (and accept a little less tire clearance), and that way you can get a power meter too.

The front derailleur is a sleek affair, wired to the battery in the seat post. Photo: Kevin Fickling / Shimano

Based on some hints from the Shimano product launch team, it sounds like electronic 1x12 for gravel might be in the development phase but is still a ways off. Since 2x12 GRX Di2 borrows all of its technology from the brand’s road groups, it was a logical next step after the update to the mechanical groups last year, whereas a 1x12 group will require a redesigned system.

Customization and “Front Shift Next”

If you’re not familiar with the Di2 ecosystem, it’s a little complicated to explain all the possible iterations of shifting options available. Using the E-Tube app, you can choose from one of three primary shifting modes: manual, semi-synchro (the rear derailleur automatically adjusts to minimize the jump in gear ratio when you shift the front derailleur), or full synchro (the front derailleur shifts automatically when the rear reaches a certain gear on the cassette). You can also change the speed of shifting.

Hidden button (top, on the inside of the hood) and satellite sprint shifter (lower, peeking out from the bar tape). Photo: Cy Whitling

There’s a hidden button on the inside of each hood, and as if that wasn’t enough, GRX is now compatible with satellite shifters that can be purchased aftermarket and go anywhere on your handlebar. I tried out a bike with satellite sprint shifters installed in the drops and because I usually descend in the drops, I really liked being able to shift securely on fast downhills.

Photo: Kevin Fickling / Shimano

Along with the GRX Di2 announcement, Shimano released their “Front Shift Next,” a firmware update for all Di2 systems. The update allows any single switch to move the front derailleur into whichever gear it’s not currently in. I tried it out on the stealthy left hand hood button and it was impressive–any haphazard mash of the button would instantly shift the front derailleur onto the other chainring, up or down.

With this dizzying array of buttons, you can program each to do exactly what you want it to, including switch screens on your bike computer and turn on your lights.

So where’s the battery?

The cylindrical Di2 battery is designed to fit into the seat post or seat tube. It’s bigger than the rear derailleur-mounted SRAM AXS battery but its power is supposed to last much longer (Shimano says a thousand kilometers of heavy shifting between charges). Each brake lever contains two coin cell batteries (1632) and shouldn’t need to be replaced more than once every two to four years. Battery life can be monitored on the E-Tube app or by pressing and holding a button on the rear derailleur and on the levers.

The battery lives inside the seat tube, so you'll still need to fish cables to the front and rear derailleurs, but you don't have to deal with routing them from the head tube. Photo: Cy Whitling

Because it’s wired to the derailleurs, the Di2 battery (product name DN300, cost: $185) is not something you’re pulling out all the time. The built-in battery means that you can’t absentmindedly leave it behind when you’re driving to ride somewhere but unfortunately it also means you can’t carry a spare battery just in case. The charging port is on the rear derailleur–to charge the system you need to find an outlet near where your bike lives, rather than bringing the battery inside to charge. That Di2-specific charging cable costs $50 too, so don’t lose it.

Charge your whole drivetrain through your rear derailleur. Photo: Cy Whitling

Shimano does not offer or recommend a wireless dropper post in its Di2 system, and because the 2x12 levers don’t have a swing action, they can’t be used to actuate a wired dropper. One possibility is to program the shifters so that all action takes place on the right hand, and then run Shimano’s left hand mechanical GRX dropper lever or use an actuator that attaches elsewhere on the handlebar. However, the battery is in the way of where a dropper would be, and to find workarounds you have to look to Reddit. The recommended hacks there seem questionable at best.

Shimano's GRX shifters feature textured, contoured hoods, and two buttons on each paddle, differentiated by position and texture. The ergonomics of the hoods are excellent, but I sometimes struggled to find the right button. Photo: Kevin Fickling / Shimano

While the road and gravel cockpits are now wireless, Shimano’s mountain bike Di2 systems are still fully wired. The XT Di2 12-speed HyperGlide+ and 11-speed LinkGlide drivetrains are only compatible with e-bikes (and we didn’t hear a peep about future plans on that front).

In Conclusion

Shimano’s updated 2x12 GRX Di2 isn’t groundbreaking, it’s a refinement of previous generations of the brand’s excellent gravel groupset, paired with the high-tech trappings brought over from the Di2 electronic road drivetrains. So how does it ride? Check out my first impressions here.