SHIMANO’S GRX Di2 GRAVEL GROUPSET BRINGS MUCH OF THEIR ROAD PROWESS AND ADAPTS IT BEAUTIFULLY TO DIRT

Words and Images - James Raison

We were lucky enough to get our hands on a set of Shimano’s brand spankin’ new gravelicious GRX Di2 groupset in January. Since then, we’ve built it up and thoroughly beat it up. After a few months of mistreating an expensive drivetrain we’ve got some thoughts on Shimano’s first push into the growing gravel scene. There’s plenty to cover so let’s jump right in!

BUILD

Groupset:

Shifters: ST-RX815 - $1,299 including brakes
Crankset: FC-RX810-1 40t - $399
Rear derailleur: RD-RX817 - $549
Cassette: CS-M8000 40t - $179
Brakes: BR-RX810 - included with shifters
Rotors: SM-RT800 - $89 each
Battery: BT-DN110-A - $229
Junction box: EW-RS910 bar end plug style - $189
Extra for cables.

The Bossi Grit Ti was me weapon of choice with Shimano’s GRX Di2

The GRX was built onto a proud Aussie Bossi Grit Ti. It was used with Shimano’s GRX RX-570 wheels which we also reviewed, and a set of Bossi’s own RD1 wheels. Overall it made for a beautiful, clean build. Exactly the sort of bike you’d expect GRX Di2 to appear on.

SHIFTING

I love what Shimano has done with the GRX shifting operation, more so than the shifting itself which is classic Di2.

The shift buttons seem to grow with every iteration which is fine by me

I kept the shift settings to their out-of-the-box default. It’s the familiar Di2; accurate, perfectly consistent, and neither quick nor slow. Getting Di2, whether road or GRX, means you can largely abdicate responsibility for your shifting decisions. Mash a shift button at almost any time and the drivetrain will sort itself out. Even when chewing stem on brutal gravel climbs I could flail at the buttons and the derailleur would dutifully move cogs without fuss. It lacks the romance and artistry of well-executed mechanical shifting but you don’t buy Di2 for that anyway.

The textured part of the shifter is a button that became my favourite way to shift gears

Let’s move onto what GRX adds to Shimano’s Di2 shifting. The familiar Shimano Di2 shift buttons are still here, but they’ve moved the shifter-top buttons from the road levers onto the inside of the hood, pictured above. It’s placed slightly above where your thumb sits. That button, and the regular shift buttons, can be mapped for different functions using Shimano’s E-Tube software so I chose to make every button on each shifter perform the same function. It’s a 1x system without a D-fly so all I needed was basic shifting. So I set all 3 buttons on the right shifter to move the chain to the right, and all buttons on the left shifter to move the chain to the left. I’ve basically SRAM-ed the shifting. That means I can hit any button on each shifter and it’ll shift in that direction. That extra button became my favourite one to use because you don’t have to relax your finger grip. Just lift your thumb and squeeze. It’s very handy when you’re climbing or just trundling along the gravel road. I love this system.

GRX hasn’t really changed Di2 shifting; just refined the hardware to give you more ways to map your shifting functions.

ERGONOMICS

Shimano has, and I don’t say this lightly, designed the most comfortable hydraulic shifters I’ve used by quite a wide margin. They are amazing, eclipsing all of Shimano’s road shifters, and Campagnolo’s outstanding Record 12 Disc design.

They’re fantastically comfortable at the hoods, with sympathetic sculpting to reduce stress on the fleshy part of your hand, some subtle texturing for grip, and added length compared to most hood designs. I have larger than average hands and appreciated having more to hang onto. They’re comfortable to wrap your fingers around too. Each iteration since the rudimentary-in-retrospect R785 design has brought small improvements. The GRX’s ST-RX815 shifters are the finest on the market for all-round comfort, not just the best for Shimano.

The GRX shifters matched well with PRO Discover Medium Flare handlebars

They’re still comfortable when angled for gravel bars too, which makes sense given how popular and evermore crazy gravel handlebars are getting. I used them on a set of Pro DIscover Medium Flare bars (which are excellent) which have a 12° flare. They’re far superior to SRAM’s mechanical shifters generally, but especially on an angle when the SRAM blockiness gets less comfortable.

I’m crossing my fingers that the GRX ergonomics cross over to road shifters. They’re not pretty but I will trade looks for this comfort every day of the week.

BRAKING

There’s excellent power and consistency in the braking system. Shimano adapted the servo design from their MTB levers to give more power for less lever throw. You can notice it too. I threw the Bossi down some steep and loose descents and never felt a lack of power, and didn’t find myself locked up and sliding.

The RX815 shifters moved the pivot higher in the lever meaning you get much more leverage when braking on the hoods compared to their road Di2 shifters. There’s a short lever throw to get your braking power too, another improvement over older Shimano hydro shifters.

Brake calipers are badged GRX but are ostensibly the same dual-pivot design and work with the same pads and rotors made for the road. That’s fine by me, because the improvements have been made in the shifter which makes the whole system feel better despite re-used parts. On the rotors, I found they managed heat well but did sometimes overheat. On occasional gnarly plummets needing firm and constant braking for control they’d often take some time to cool down and recover. It was generally rare though.

Brake noise has been the closest to silent I’ve had with disc brakes. A whisper is all I get when hitting the skids. When wet, the whisper got slightly louder. There has been no screaming or screeching at all. I’ll add the caveat that the Bossi frame had its brake mounts properly faced when it was getting built, a process I featured in this article on why Facing is important but almost nobody does it, which is crucial to ensure caliper alignment is correct which does wonders to make brakes quiet. So the message here is that a proper build and install will let the Shimano brakes function properly, and be the quiet brakes you’ve always wanted from discs.

During the months of testing the only maintenance I’ve done is straightening a rotor. The front brake could do with a bleed but there’s still ample pad left in both calipers. No fuss, no muss.

REAR DERAILLEUR

There’s plenty to talk about with the rear derailleur, both good and not-so-good.

Starting with its shadow-inspired profile. Shimano has done an excellent job giving the beefy shape a low external impact. The derailleur tucks in close to the frame. That means it’s more protected from taking hits, and won’t obliterate your derailleur hanger if the bike takes a tumble onto the drive side. That matters with gravel riding and bikepacking. I’ve managed to bend a hanger on every bikepacking trip I’ve done so I’ll take every tweak designed at resilience I can get.

I have mixed feelings about the clutch mechanism. It’s quite slack out of the box and I noted more chain bounce than I’d expect from a clutched derailleur. I even managed to throw the chain off the front ring on a particularly bumpy descent. After that I tightened up the clutch; a simple process that involves popping open a small port and winding on tension with a hex key. After that it was much firmer, but there’s a friction cost that comes with it, which I talk about below.

The Clutch in the ON position. Occasionally I found it slid behind the cage occasionally

The clutch lever had a strange tendency to drop into a third position. There’s the standard ON/OFF positions you can click between, but every few rides I’d see it had moved beyond the ON position to sit slightly behind the derailleur cage. I’d have to dig it out carefully with a small hex key or whatever other tool I had at hand. The clutch is still on, but it’s an inconvenience to move it back to the regular spot. Its movement beyond normal positioning has also marked the derailleur cage slightly which could annoy some people.

The rear derailleur has some cool design, but that clutch has been a little iffy in my months of testing.

FRICTION

There’s a mix of factors, the clutch being one of them, that gives the GRX noticeable drivetrain friction. When on the granny gear you can feel resistance as the clutch and extreme chainline angle add up to drivetrain pressure when you turn the cranks backwards. You can feel far less friction doing the same test with a SRAM Apex and Force 1x drivetrains. That friction disappears into pedalling effort on the bike, but it’s something worth noting. Shimano isn’t quite on SRAM’s level with their smoother clutches and bendy chains.

FROM THE PARTS BUCKET

Shimano has chosen to use some existing assets to complete the GRX parts ecosystem which means most perishables are already widely available, and the tier system means there’s multiple price options. That suits the gravel riding ethos where perishable parts tend to need replacement more often. It’s undoubtedly a strength for GRX. The running costs of GRX Vs Force AXS will be very different over a few years thanks to Shimano’s decisions to keep some hardware choices simple. Compare an M8000 cassette to a SRAM Force 12 speed and you’ll see what I mean. It’s a substantial difference.

So, the good news is that all existing 11 speed road and MTB cassettes, chains, brake pads, and Di2 electronics are compatible. There’s no need for a new freehub either. You need only adhere to the recommended cassette to derailleur compatibility depending on your single or double drivetrain choice to stay within manufacturer recommendations.

Now, I’m going to argue against myself about a lack of innovation.

1X11 IS NOT VERY 2020

Having just lauded Shimano for keeping GRX simple, I think the 1x option is perhaps a little too simple.

1x11 with cassette topping out at 42t is not where I want to be in 2020 when there’s a 2x option. I think a 1x12 is the crossover where I’d consider buying a 1x drivetrain over a double drivetrain. I always felt a gear short at both ends of the cassette. SRAM’s 12 speed AXS ecosystem lets you fit an Eagle 10-50 cassette/derailleur with a single front chainring and road shifters for gravel builds. Expense aside, that’s an amazing option to have, and covers my full range of riding.

I caught up with Jayson from gravelcyclist.com in January and we were able to have a look over each others’ GRX Di2 drivetrain. His T-Lab had the 2x version and I was very jealous!

I haven’t tested the 2x GRX yet, but I expect it’s got all the excellence of their road groupsets. That’s the groupset I’d want to get. For me, the simplicity of the 1x has to offer a minimum range before I’d take it over an equivalent 2x, and that range isn’t here. The gravel market was moving towards 1x as the chosen drivetrain format but I think GRX will swing it back to 2x because Shimano is so damn good at consistent and reliable front derailleur shifting.

THE RIDE

Despite everything above, I want to talk about how completely seamless the GRX Di2 ride is. Your equipment should always facilitate the enjoyment of riding a bike and never detract from it and GRX Di2 has done exactly that.

The excellent ergonomics improve your hand comfort, as does the small input needed for brake power. You don’t have to think about shifting because it’s so reliable and consistent. Only when I noticed my chain whacking away at the bike frame was I distracted from enjoying the ride. Tightening it up did improve it, but didn’t entirely eradicate it.

The Bossi and GRX groupset have done the full spectrum of gravel riding from short trail loops, up to 10 hour days getting properly regional. As yet the only untested area is bikepacking which has been on pause for a couple of months. I’d have no hesitation adventure riding with GRX Di2. The Di2 battery life is massive and I don’t see any potential issues in the rest of the drivetrain.

VIDEO

WRAPPING UP

Shimano’s GRX Di2 is the refinement of existing strengths within Shimano’s drivetrain line-up. They’ve largely taken what they know, and adapted it to the new discipline. The shifting is unsurprisingly excellent, the brake system is a clever adaptation to the rigours of gravel, and the ergonomics are outstanding.

It may not represent great innovation, but the gravel and adventure market is far more likely to favour simplicity, reliability, and cost over new and radical. My only function gripe is in that clutch design and the drivetrain friction I found. That’s an area that needs improvement.

Otherwise, Shimano’s big push into the booming gravel market is impressive. This GRX groupset with its many variations is going to be everywhere before long with people upgrading their current bikes and buying new rigs with GRX builds. It took them a long time to get it out, but Shimano GRX is definitely something the gravel market needed and something buyers can rightly look forward to using.

Disclosure statement: This groupset was sent by Shimano Australia for review.