Colin reviews the Shimano GRX Di2 Groupset

Shimano unveiled its GRX Di2 gravel groupset roughly a year after it gave the mechanical version of the group the 12-speed treatment.

That groupset brought Shimano up to — 12 gears both 1x and 2x — and saw the Japanese outfit begin to close the gap on SRAM in terms of range.

At the launch event itself, the Shimano crew were pressed by multiple editors about where Di2 was, and the murmurs circulating through the bunch was one giant question mark that overshadowed the new parts. The clearest answer we could get was ‘it’s coming’, and that was it.

Related:

• New Shimano GRX 820 12-Speed Review | Boring but brilliant
• 2024 Cervelo Aspero Review | Cervelo’s new gravel racer is just peachy
• 2025 Giant Revolt Advanced Pro 0 Review | A versatile gravel shredder that’s easy on your body

For better or worse, Shimano has always been a brand that moves at its own pace, and 12-speed GRX Di2 did, in fact, come, breaking cover in May of this year as 2x only. While we now have answers to the first big query, that double chainring on the front has left us with more questions. Reframing those questions, however, might just reveal something about the long-awaited XT/XTR update.

For the last six months or so, I’ve been testing the new GRX Di2 groupset, and its performance has me salivating about what could be to come.

An overview of Shimano GRX Di2 and what’s new?

The latest iteration of Shimano GRX Di2 sees much of the electronics seen in its road groupsets trickled into the drop bar gravel setup.

Beyond the fact that Shimano has brought its servo motor-based shifting to 12-speed for gravel, the major headline here is that, for the time being, it’s 2x only. This omission of 1x shifting for gravel is notable. Shimano’s official line is the familiar moniker of ‘it’s coming.’

When Shimano unveiled this groupset, I wondered aloud if the lack of GRX Di2 1x was because the new mountain bike groupsets would once again make the jump to Di2 and play nice with GRX. A few months on, you’ll find me with the most enormous tin foil hat you’ve ever seen firmly planted atop my noggin. I am convinced this is the case — more on this later.

Like the mechanical GRX, some of the parts are carried over from the previous generation, namely the crankset, which is, beyond the chainrings, the same as the 1x group and the previous generation 11-speed GRX.

The brake callipers are borrowed from the mechanical group, the cassettes are 105 and Ultegra, and the chain is your standard XT/Ultegra M8100 unit.

Less wires, but not entirely wireless

Shimano has adapted the semi-wireless protocol seen on its road groupsets to GRX Di2. This means that a cable connects the derailleurs to a battery housed inside the seat post. Shimano claims it should last between 1,000km and 1,500km. So far, in six months, I’ve charged it twice.

With the battery hidden inside the frame, everything must be charged in situ. While Shimano has always run Di2 with one larger battery, it’s not a surprise this system has continued.

The shifters on the other hand, are wireless and powered by a pair of CR 1632 coin cell batteries, which are said to last four years. You can still hardwire the shifters if you’re worried about reliability, outright shift reaction time, or some bad actor hacking your groupset and taking over your shifting. In practice however, there really isn’t any reason to do so.

Bar the brake hoses, all of the other cables are sequestered to the rear triangle. These dainty wires are completely rattle-free thanks to Shimano’s not exactly elegant, but definitely effective EW-SD50-I cable ties that you stuff in the frame to damp any sound or vibration.

Speaking of those shifters, the ergonomics have been tweaked, and Shimano has updated the multi-function button on the inside of the hood, which can be used to shift or do things like scroll through the pages on your Garmin or Wahoo computer.

The whole kit and kaboodle is now based around the rear mech which is the brain of the operation, and replaces the junction box which previously needed to be stored somewhere on the bike.

The front derailleur is new as well and, like its predecessor, has been optimised for 17-tooth jumps to match the ratio Shimano has settled on for its 12-speed front chainrings.

Shimano GRX RX825 Di2 Prices

Starting from scratch, a full GRX Di2 groupset will cost you $3,341.83 AUD. Though if you’re upgrading from 11-speed you don’t need a crank, you will need chainrings. That’s $1,180 AUD more than the mechanical group costs. For context, a SRAM Force AXS 2x group will cost you $3,317 AUD.

• RX 825 Right shifter w/ Brake Caliper and hose | $649.99 AUD
• RX 825 Left shifter w/ Brake Caliper, hose and adaptor | $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
• CS HG710-12 cassette, 34-11T | $179 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

Shimano GRX Di2 weight

And while we were looking at individual components, here are the actual weights of everything according to the Flow Scales of Truth™. Funny enough, quite a few of the components were a handful of grams under the claimed weight, which is the opposite of how things usually go.

And while we were handing out kudos, the distinct lack of plastic in the packaging should be commended. All of the boxes are designed so that bubble wrap and the like aren’t needed, and small parts like lock rings and washers come in paper envelopes.

• RX 825 Right shifter | 220g
• RX 820 Front Brake Caliper w/ hose and adaptor | 167g
• RX 825 Left shifter | 220g
• RX 820 Rear Brake Caliper, w/ hose | 160g
• RX 820 Crank 170mm | 700g
• RX 825 Rear derailleur | 309g
• RX 825 Front derailleur | 138g
• CL-800 Rotors front and rear | 228g
• CS-HG710-12, cassette 34-11T | 340g
• CL 800 Rotor 160mm | 112g
• CL 800 Rotor 140mm | 94g
• BT-DN300 Battery and wiring harness | 75g
• Total | 2,763g

GRX Di2 Ergonomics

The GRX Di2 levers are an ergonomic marvel and, and to my hands, are the most comfortable drop bar levers out there.

With a shape resembling the head of a xenomorph from the 1979 cinematic masterpiece Alien, Shimano has only slightly changed the ergonomics of the Di2 levers for this group. The ‘hook’ at the top of the hood has been slightly reduced, and its girth front to back has been increased. The important thing here is that it still creates the sensation of being locked into the hoods. There is also some subtle shaping on the inside of the hood that gives your thumb a nice place to rest.

Along with the form of the previous Di2 lever, it allowed Shimano to raise the pivot point of the lever blade (which is finished in a non-stick coating borrowed from the fishing side of Shimano’s business) higher in the assembly. This provides more leverage at the hoods and significantly more control than SRAM’s Force AXS levers  The action is light, with a well-defined contact point followed by a strong bite, with easily modulated power. I haven’t personally used the new Red AXS XPLR, which claimed a similar benefit allowing for one-finger braking, so I can’t offer a real-world comparison just yet.

The rubber hoods also have some texture under your palm and where your fingers wrap around underneath the lever. The first-generation GRX ribs always gave me blisters, but Shimano has toned it down a touch, and I can happily ride all day without gloves.

There is enough room to comfortably fit three fingers behind the lever blade and an ample amount of reach adjust to make the setup comfortable for smaller mitts.

Shimano also says the transition from the bar to the hoods has been made rounder in shape to create a larger surface area and eliminate pressure points. This is not something I can say I noticed. Something I did notice however is that the reach on these levers is longer than on the mechanical levers, so it is a factor you’ll have to consider when it comes to bike fit.

Servo motors + HG+ = top notch shifting

Unsurprisingly when you combine servo motors with Shimano’s Hyperglide+ cassettes, the shifting is damn near flawless. Fast, crisp and accurate regardless of whether everything is surgically clean or caked in mud and with a chain that hasn’t been lubed in a fortnight.

When you are just cruising along, sometimes rear shifts are so seamless and quick, it’s hard to actually tell that anything has happened. Under power, the shifts are precise and unwavering. Not quite to the level SRAM Transmission will eat a poorly timed shift without making a fuss, but we’re splitting hairs here.

We rarely talk about front shifting nowadays here on Flow, but Shimano has always been on the front end of the pack here. That’s not to say you can’t confuse the new front mech, but dropping the chain on this Di2 setup is extremely difficult. Jumping 17 teeth is no easy task, and even purposely moving the chain up and down through eyeball-rattling rough sections while cross-chaining, I haven’t managed to send it over the edge yet.

Of course, the clutch — or chain stabiliser, as Shimano would prefer we call it — is in part worthy of praise in this instance, too. But I digress.

Including the new button on the inside of the hoods, there are now three buttons on each side, which can be programmed for shifts and controlling your computer or light, which is all done through the E-Tube app.

Looking at the shifters, the actual buttons are more pronounced than the previous version, and the texture has changed from dots to stripes, which combines to make them easier to recognise — especially with gloves on. I do wish that Shimano would pump up the haptic feedback, as the click is akin to that of a computer mouse.

Front Shift Next

The new GRX Di2 carries over Shimano semi-auto shift modes Synchronized and Semi-Synchronized shifting. These launched as far back as the original XT Di2 and never really caught on.

Front Shift next, however, is new, and with this fresh shift mapping enabled, the front derailleur will put the chain where it isn’t when you press the button — regardless of whether that is up or down. This means you only need one button to look after your front shifting, freeing up space for other things.

I played around with this a fair bit, emulating a form of SRAM’s shifting arrangement and moving things all over the place to see where it would be the most useful. As it turns out, the new multi-function button on the hoods was the ideal spot.

I tend to eat and drink with my left hand, meaning I can move up and down the cassette while stuffing my face. Quite often, I’ll hit a pinch and run out of gears while still trying to get food in. Being able to swap that front chainring with my right hand is pretty handy.

GRX Di2 Gearing

The gearing is the same as the 2x mechanical groupset with the RX820 level chainrings, which 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 those riders with a diesel engine. Third-party outfits like Wolf Tooth components offer bigger rings as well.

At the back, Shimano borrows the 11-34T Ultegra cassette with Hyperglide+, while the 11-36T is taken from the 105 product range and misses out on the fancy ramping that makes a real difference to shift quality. Officially the rear mech is limited to 36T.

I’ve been riding the 48-31T combo paired with the 11-34T cassette, which provides ample range for most folks (myself included) and small jumps between the gears. With the 1x version, I mentioned that about two-thirds of the way down the cassette — between the 21T and 14T cog — I was often left searching for a gear, unable to find a comfortable cadence at cruising speed.

I chalked this up to the two to three-tooth jumps between the gears — SRAM’s 1x cassettes are the same. Unsurprisingly, with the one to two tooth jumps available on this section of the 11-34T cluster, no such searching was required.

I didn’t find myself often spun out, however sometimes having a slightly larger gear to push when you’re motoring through a rough section can take some of the pressure off the saddle for a little bit of comfort. With the 48/11T being the biggest ratio available, occasionally, I did find myself wanting the 10T you get on a SRAM cassette seeking relief.

On the flip side, the 11T cog means these Shimano cassettes play nice with a standard HG freehub body, so for those upgrading from 11-speed, there is no faffing about needed. Bang that lockring in and go.

What about GRX Di2 1×12? Colin’s blue-tinted tin foil hat and what it could mean for the MTB groupsets

Much ink…errr pixels…have been spilled about the lack of 1x GRX Di2. If you’ll allow me to don the tin foil once more I will run through my full Shimano GRX Di2 1x conspiracy theory.

Shimano’s MTB groupsets are a bit long in the tooth and well overdue for a revamp. Given we’ve seen Specialized and Santa Cruz launch frames that don’t have holes to route mechanical groupsets, there has to be a wireless electronic groupset coming from Japan.

There is simply no way that these two industry behemoths have cornered themselves into just working with one component supplier for OEM. From a business perspective, it doesn’t make sense.

It also doesn’t make sense to launch an MTB-shaped derailleur, capable of shifting a chain onto an MTB-shaped cassette with a 51T cog for gravel, when the MTB groupsets are theoretically overdue for a glow-up.

As it currently stands, all 12-speed Di2 components can talk to one another. So you can pair GRX Shifters with Dura-Ace, Ultegra or 105 derailleurs.

Still with me? Great, because it’s time for my grand 1x Di2 conspiracy manifesto. As I laid out in the launch piece back in May, I believe that the new generation of Shimano MTB components will be Di2 and wireless. AND I think that the electronic derailleur will be compatible with GRX.

But wait, I’m not done yet — hang onto this red yarn and box of thumbtacks, would ya? Given Shimano’s current bent on building its latest gear around current staples that already work extraordinarily well (see the crank), I think it will utilise the same Hyperglide + chain and cassette we have now. Given that both of the latest generation GRX groups, mechanical and 2x Di2, follow this trend, I can’t see why Shimano would throw a curveball.

Of course, there are some holes in my theory and things I do not have answers to. Will it be a hanger-less setup like SRAM’s T-Type Transmission?

My instinct would say yes, given a 2022 Shimano patent that shows a “coaxially” mounted derailleur.

Then there is the battery. Looking to the road for a moment, when Campagnolo launched its latest wireless Super Record groupset, the batteries are specific to the front and rear derailleur. Campy says that navigating the plethora of patents held by its competitors made it an insurmountable task to come to market with a universally interchangeable battery.

As it stands, the current seatpost-mounted Di2 battery poses an issue because everyone is running a dropper post. Shimano does have a solution for storing the battery in the steerer tube, but of course, that requires a wire to run from the rear dropout to the head tube, and still doesn’t address these frames that lack the holes for such a connection.

A 2023 Shimano patent does show an interchangeable battery design, but like Campy, these appear to be component-specific.

So all of this is to say, I will eat my hat if the next generation of Shimano MTB components aren’t wireless and don’t speak the same language as the GRX shifters to make for a 1x Di2 gravel groupset.

Of course, this is all speculation, and trying to read the tea leaves using patent documents which I understand about as well as my two-year-old comprehends a macroeconomics textbook.

So I shall wrap this up in the way that all good conspiracy theories end — do your research kids.

Flow’s Verdict

Shimano’s GRX Di2 is nothing short of fantastic, but it’s difficult to look past this performance being limited to 2x.

SRAM is well and truly ahead in this respect. Want a 1x gravel group? Have your choice between 12 or 13 speeds and multiple gear ranges. Keen for 2x? No worries, that is available too, and here are three sizes of chainrings.

SRAM is very good at listening to what the market wants and getting that on bikes surprisingly fast. Shimano often takes longer to do the same things, but the result is usually a more refined product.

Does that highly refined gear matter when your main competitor has already taken up all the air in the room? That’s a question I can’t answer.

And what Shimano has produced is nothing short of brilliant! The shifting is fast and accurate regardless of how hard you’re pushing on the pedals. The brakes have oodles of power on tap but aren’t short on control, and those funny-looking hoods make for a locked-in and comfortable place to rest your hands for hours.

As someone who perpetually forgets to charge things, I can appreciate the larger capacity battery hidden in the seat post. It also can’t be lost, and it’s a heck of a lot more protected from water and blunt objects. But living in the seatpost complicates things if you’d like to jam a dropper into the seat tube. For someone motivated enough, there are ways around this problem, but it’s an inherent issue with the system — albeit one that isn’t going to trouble most gravel folks.

It’s not a game changer or revolution or any other highfalutin buzz words, but GRX Di2’s performance is nothing short of fantastic. And if you’re in the market for a 2x gravel groupset, there is no better option.

ABOUT THE REVIEWER - Colin Levitch

Hometown

Gold Coast, QLD

Height

175cm

Weight72kg

RIDING STYLE

Aggressively mediocre