First Look | Shimano GRX Di2 12 speed

Last year Shimano updated their GRX gravel groupset to 12-speed, along with a host of other changes. Given that SRAM had added an extra cog a few years ago and Shimano had also dropped 12 speeds down its MTB and road groupset, it wasn't exactly a surprise.

What it was surprisingly however, the review was limited to GRX machines. At the launch event, Shimano was pressed to say that the GRX Di2 is coming, but he had nothing else to say.

However, almost twelve months later, the big blue S lifted the veil on the GRX Di2. We have a bunch of teams on the way that will be tied to our Cervelo Aspero long-term tester, but for now, here's what you need to know.


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

Small wires, not wireless

One of the best parts about SRAM's AXS drivetrains is that they are literally plug-and-play. By that, I mean you close the derailleur and open, and that's it. The rear brake hose is the only thing you have to move to the frame. All other communication is in the air. No connections to rattle loose or junction boxes.

Turn it on, turn on the battery, and away you go. The downside is that each piece needs its own battery.

Shimano's Di2 typically runs everything from a single battery, which is wired directly to all components via a junction box. Although the latest XT Di2 – for e-MTB only – is still fully wired, the road groups go wireless in 2021 and now this system has been forgotten on the GRX Di2.

This means that the shifters are powered by 2x cell batteries (which are said to last between 3.5 and 4 years!), and the derailleurs are wired directly to the main battery that sits inside your saddle. This larger battery is said to last between 1,000km and 1,500km, depending on your driving habits.

While the dropper post increase isn't huge on all gravel bikes, the battery sitting in the seat makes things difficult – although there are workarounds.

Toby Shingleton of Shimano, Australia, noted that PRO makes an expander cap that allows you to bend the battery into the steerer tube. He also notes on some frames, you can run on the top tube and snap the ropes again.

Shimano chose CR1632 batteries for the shifts. These have the same diameter as standard CR2023 batteries but are 4mm shorter. So you won't be able to scrub one riding your buddy with a spare of his SRAM shifts.

The front mech reveals it all – maybe

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

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

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

Given the popularity of the 1x for gravel, the GRX machine not only has a 1x but can be run with up to a 10-51T cassette. Tricking that 10T cog into a hub provided the impetus for wheel brands to start offering Microspline freehubs for road and dirt wheels; it doesn't seem like a huge logical leap to think that this is where the product is headed.

Of course, the theory starts to get a few holes when you remember a mid-2022 patent from Shimano that shows a “coaxially” mounted rear mech. Given the wave SRAM made with the Transmission, it's not too much of a stretch to expect Shimano to respond in kind. Of course, this is just speculation, so only time will tell.

GRX Di2 Gearing Options

Now that we've had a chance to indulge our conspiracy desires let's get back to what we really know – gear.

Using the same crank and 1x system—and 11-speed—the RX820's chainrings are a 48/31T combo, while the RX610's are a 46/30T combo. Although the GRX uses a +2.5mm chainline, it's still compatible with road cranks so the big dogs with engines can push big gears.

Similar to the GRX machine, Shimano lends cassettes to road teams. The 11-34T is available with Hyperglide in Dura-Ace and Ultegra spec, while the 105 version with the 11-36T cassette does 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 VERY FAST, clean and precise. And the two-button switch is done again. However, with the E-Tube Project app, you can customize what the buttons do and toggle Synchro and Semi-Synchro shifting, which sees the front mech shift automatically as you move up and down the cassette when you hit extreme gear ratios. .

Rear derailleur captain ship GRX Di2. An episode connecting shifters and derailleurs, talking about the E-TUBE app, cycling computers, and more. This is where you'll charge the groupset, check the battery level, and pair up new bits and pieces like satellite shifts.

Shimano GRX Di2
The GRX derailleur sees the same variable clutch – or chain tensioner according to SRAM's preferred nomenclature – as the MTB and gravel groupsets.

It is said to weigh 310 g, and is outfitted with the brand's Shadow RD+ Chain Stabilizer (AKA clutch).

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

This frees up a shift button that can be assigned to lights, scrolling on your computer, or even copying SRAM's AXS shift map.

Shimano has also carried over the multi-function button that has graced Di2 Shifters since the early days. At first, it was on the hoods; However, it has been moved inside for easy access with your thumb. Using the E-Tube App, this can be given to do anything that the big buttons on the level do.

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

The shift levers themselves have also been updated but retain their silhouette. One of the biggest criticisms of the mechanical GRX was that the instruments were nowhere near their electronic counterparts, with the Di2 version offering a more confined feel in rough terrain and more brake control from the hoods.

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

The hoods also have raised ribs for added leverage, and the lever blades feature anti-slip features borrowed from Shimano's fishing division.

Shimano GRX Di2
The GRX Di2 levers are slightly different in design from their mechanical counterparts, and we're big fans of the fit and feel of the previous version.

GRX pedals

Shimano presents a special edition set of GRX pedals alongside the new group. They are completely different from the XT pedal, Shimano just put them together We met at Gravel graphics.

Shimano GRX pedals
Although the graphics on the GRX pedals look good, they are no different than the XT pedal.

As we mentioned above, we've got a full collection of GRX Di2s headed to Flow's QLD HQ and we'll be putting them on Peaches and our long-term Cream Cervelo Aspero test bike.

GRX Di2 price, availability and weight

The GRX Di2 is available from retailers now, and if you're looking to upgrade to a full team kit it'll cost you $3,341.83 AUD — including all the individual pieces.

Here's how the price works out for the components and the additional pieces you'll need:

  • RX-825 Right shifter w/ Brake Caliper, hose $649.99 AUD
  • RX-825 Left Shifter w/ Brake Caliper, hose & adapter $649.99 AUD
  • RX-820 Crank 170mm, 172.5mm, or 175mm $349.99 AUD
  • RX-825 Rear derailleur, $560.99 AUD
  • RX-825 Front derailleur $289.99 AUD
  • RT CL-800 Rotors front and rear $179.98 AUD
  • Cassette CS-HG710-12,12-speed 36-11T $145.99 AUD
  • M8100 12-speed chain $74.99 AUD
  • EW-SD300, 900MM Di2 Wire $34.99 AUD
  • EW-SD300, 1200MM Di2 Wire $34.99 AUD
  • BT-DN300 Battery $299.99 AUD
  • EW-EC300 Charger $69.95 AUD

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

  • RX-825 Right shifter w/ Brake Caliper, hose 415g
  • RX-825 Left Shifter w/ Brake Caliper, Hose & Adapter 415g
  • RX-820 Crank 170mm, 172.5mm, or 175mm 721g
  • RX-825 Rear derailleur, 310g
  • RX-825 Front derailleur 142g
  • RT CL-800 Rotors front and rear 228g
  • Cassette CS-HG710-12,12-speed 36-11T 391g
  • M8100 12-speed chain $74.99 AUD 247g
  • EW-SD300, 900MM Di2 Wire 7.25g
  • EW-SD300, 1200MM Di2 Wire 7.25g
  • BT-DN300 Battery 53g
  • Total claimed weight: 2.52g

Before we tie everything to the Aspero, we'll review this with the actual weights of each piece. Stay tuned folks!

Cervelo Aspero
We will be swapping the GRX Di2 set for this Cervelo Aspero. Stay tuned for the full review.

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