First Look | Shimano GRX Di2 goes 12-speed

Last year Shimano updated its GRX gravel groupset to 12-speed, along with a whole host of other changes. Given that SRAM had added the extra cog quite a few years prior and Shimano had also trickled 12-speed down its range of MTB and road groupsets, it wasn’t exactly a surprise.

What was a surprise however, was that the update was limited to GRX mechanical. At the launch event Shimano was pressed and said GRX Di2 was coming but had nothing else to say.

Well, almost twelve months later, the big blue S has lifted the veil on GRX Di2. We have a groupset on the way that will be bolted onto our Cervelo Aspero long-term tester, but in the meantime, here’s what you need to know.

Related:

Shimano has added a cog to the back of its GRX Di2 groupset.

Less wires, not wireless

One of the best parts about SRAM’s AXS drivetrains is that it’s literally plug-and-play. By that, I mean you bolt the derailleur and shifter on, and that’s it. The rear brake hose is the only thing you have to route through the frame. Everything else communicates through the air. There are no connections to rattle loose nor junction boxes.

Bolt it on, wang the battery in, and go. The downside is that each piece needs its own battery.

Shimano’s Di2 traditionally runs everything off one battery, which is directly wired into all the components via a junction box. While the latest XT Di2 — which is only for e-MTBs — is still fully wired, the road groupsets went semi-wireless in 2021 and now this system has been trickled into GRX Di2.

This means the shifters are powered by 2x coin-cell batteries (claimed to last between 3.5 and 4 years!), and the derailleurs are wired directly into a large battery that lives inside your seatpost. This larger battery is claimed to last between 1,000km and 1,500km, depending on your shifting habits.

While the proliferation of dropper posts isn’t huge across gravel bikes, the battery living in the seat post complicates things — though there are some workarounds.

Toby Shingleton from Shimano, Australia, noted PRO makes an expander cap that allows you to stow the battery in your steerer tube. He also notes in some frames, you can actually run it in the top tube and sneak the wires through as well.

Shimano has opted for a pair of CR1632 batteries in the shifters. These have the same diameter as the common CR2023 batteries but are 4mm shorter. So you won’t be able to scab one off your riding mate who carries a spare for his SRAM shifters.

The front mech reveals all — maybe

While GRX mechanical is available in both 1x and 2x, Di2 is currently limited to 2x.

As to why, we can only speculate. However, pulling on our tinfoil hats, we’re guessing it may be to leave room for an XT/XTR Di2 derailleur. Like SRAM, Shimano’s Di2 components can talk to each other, so you can pair Ultegra or Dura-Ace derailleurs with GRX shifters and vice versa.

Does the lack of 1x GRX Di2 mean that the new MTB groupsets from Shimano will be electronic?

Given the popularity of 1x for gravel, the GRX mechanical not only has 1x but can be run with up to a 10-51T cassette. Trickling that 10T cog into gravel gave quite a nudge to wheel brands to start offering Microspline freehubs for the road and gravel wheels; it doesn’t seem like a huge logical leap to think this is where the brand is angling.

Of course, the theory starts to get a few holes when you remember a mid-2022 patent from Shimano showing a “coaxially” mounted rear mech. Given the wave SRAM made with Transmission, it’s also not a giant leap to expect that Shimano will respond in kind. Of course, this is purely speculation, so only time will tell.

GRX Di2 Gearing options

Now that we’ve had the chance to indulge our conspiratorial urges let’s return to what we actually know — gearing.

Using the same crank as the 1x system—and 11-speed—the RX820 level chainrings are a 48/31T combo, while the RX610 rings make for a 46/30T combo. While GRX employs a +2.5mm chain line, it’s still compatible with the road cranks for the big dogs with the engines to push larger gears.

Same as with the mechanical GRX, Shimano borrows the cassettes from the road groupsets. The 11-34T is available with Hyperglide in the Dura-Ace and Ultegra spec, while the 105 version and the 11-36T cassette do not get the premium ramping design that greatly improves shift quality.

According to Shimano, the maximum cog the rear derailleur will take is 36T.

GRX Di2 Shifting

Shimano’s Di2 shifting has always been SUPER fast, crisp and accurate. And the dual button shifting has once again been carried through. However, with the E-Tube Project app, you can customise what the buttons do and also toggle the Synchro and Semi-Synchro shifting, which sees the front mech shift automatically as you go up and down the cassette once you hit the overlapping gear ratios.

The rear derailleur is the captain of the GRX Di2 ship. It’s the piece that connects the shifters and derailleurs, talks to the E-TUBE app, cycle computers, and more. It’s here that you’ll charge the groupset, check the battery level, and pair in new bits and pieces like satellite shifters.

Shimano GRX Di2
The GRX derailleur sees the same adjustable clutch — or chain tensioner according to SRAM’s preferred nomenclature — as the MTB and mechanical gravel groupsets.

It’s claimed to weigh 310 g, and it’s shod with the brand’s Shadow RD+ Chain Stabiliser (AKA clutch).

Shimano is also introducing what it calls Front Shift Next. This changes the mapping so that one button is assigned to the front derailleur, and pressing that will shift to the other chainring — regardless of which direction it needs to go.

This frees up a shifter button that can be assigned to lights, scrolling through your computer, or even creating a copy of SRAM’s AXS shift mapping.

Shimano has also carried over the multi-function button which has graced Di2 Shifters since the early days. Initially, it was on top of the hoods; however, it has been moved to the inside to make it easier to reach with your thumb. Using the E-Tube App, this can be assigned to do anything the main buttons on the levers do.

Shimano GRX Di2
Shimano has moved the the multi-function button to from the top of the hoods to the inside so it’s easier to reach with your thumb. You can also run satellite shifters too.

The shift levers themselves have also been updated but have maintained their silhouette. One major critique of the mechanical GRX was that the levers weren’t closer to their electronic counterparts, as the Di2 version provides a substantially more locked-in feel over rough terrain and more braking control from the hoods.

Shimano has kept the high pivot point and shape of the brake lever and blade but has updated the ergonomics to better match flared handlebars. The brand says the hoods are rounder in shape to smooth the transition from bar to hood and create a larger surface area to eliminate pressure points.

The hoods also have some raised ribs for added purchase, and the brake lever blades see the anti-slip coating borrowed from the fishing part of Shimano’s business.

Shimano GRX Di2
The GRX Di2 levers are quite a bit different in shape to their mechanical counterparts, and we are big fans of the fit and feel of the previous version.

GRX Pedals

Shimano is launching a special edition set of GRX pedals alongside the new groupset. They aren’t any different to an XT pedal, Shimano has just jazzed them up with it’s United in Gravel graphics.

Shimano GRX pedals
While the graphics on the GRX pedals look nice, they are no different ot an XT pedal.

As we mentioned at the top, we have a full GRX Di2 groupset headed for Flow’s QLD HQ and will install it on our Peaches and Cream Cervelo Aspero long-term test bike.

GRX Di2 Pricing, availability and weight

GRX Di2 is available from dealers now, and if you’re looking at upgrading the full groupset it will cost you $3,341.83 AUD — adding up all the individual bits.

Here’s how the pricing shakes out for the components and the extra bits you’ll need:

And for good measure here is how much each part is claimed to weigh.

Before we bolt everything onto to Aspero, we’ll update this with the actual weights of each piece. Stay tuned folks!

Cervelo Aspero
We’ll be swapping in the GRX Di2 groupset on this Cervelo Aspero. Stay tuned for a full review.

 

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