Shimano GRX Di2 1x12

For mountain bikers, it's been a busy month in the electronic drivetrain world, with Shimano launching the long-awaited XTR Di2 and quickly trickling down the fully-wireless technology to XT and Deore mere days later. If you somehow missed those announcements, or need a refresher and a full breakdown on the technology, riding impressions, and more, Pete has you covered for XTR and Uncle Dave got the lower-cost componentry unboxed.

In the drop bar world, it's also been busy. In the short window between the XTR Di2 and XT/Deore Di2 launches, SRAM trickled down the full-wireless, full-mount, 1x only Red XPLR 13 speed group to Force and Rival level. I reviewed Shimano's semi-wireless 2x12 GRX gruppo last year but if you wanted a wide-range one-by setup from Japan, you were limited to mechanical. The astute among you will be able to figure out this leaves Big Blue one offroad hole left to fill, with wireless Di2 technology: 1x GRX Di2, which lands today.

I've got a lightly checkered past with GRX, Shimano's flagship gravel gruppo, here on NSMB. The first gravel bike review this site ever saw - the Canyon Grizl - came with a 2x11 mechanical setup I converted to 1x using parts from Ukrainian/Polish machining company Garbaruk left me unsatisfied with its low gear resolution. I probably should have seen that coming, but it was an interesting experiment and the Garbaruk components were great.

More recently, I reviewed the Japanese giant's 2x12 "semi-wireless" GRX Di2 variant, and while it wasn't lacking in performance and will fill the needs of many riders well, the addition of batteries and electronic brains wasn't enough to overcome my general bias against using two derailleurs offroad.

Components

The spoiler here is that there's (almost) no new components here. The heart of the GRX 1x system is RD-RX827-SGS, a re-badged XT derailleur identical to the one Dave showed last week and only available in the long-cage SGS configuration. This runs a chain up and down the same CS-M8200-12 cassette; if you're using the GRX derailleur, you're constrained to the 10-51 variant. User input is enabled by the ST-RX825 brifters I reviewed as part of the 2x system. The BR-RX820 brakes are unchanged (they do not use the new low viscosity fluid), and the FC-RX820-1 crankset is pulled from the existing 1x12 mechanical GRX gruppo, available with 40 or 42 teeth, and in 170, 172.5, and 175mm lengths. The only new component available today is BL-RX825-L, a left side brake lever that eschews any electronics and cabling for cost - and weight savings.

Effectively, this is what gravel folks refer to as a 'mullet' setup - with drop-bar brifters paired up to a 1x mountain bike derailleur and cassette for a wider gear range. Bikepackers and touring folks have been cobbling together various solutions to do this with cable-operated systems for years - bikepacking.com has a good breakdown from 2021 of options that existed at the time. I used a kit from Ratio Technology to convert my SRAM 1x11 1-42 Force drivetrain to shift a 1x12 Eagle derailleur over a 10-52 cassette in 2018; from 2019 onwards folks who ride SRAM have been pairing AXS mountain components with AXS brifters, and these setups have won everything from Unbound to Leadville under guys like Keegan Swenson, and helped bikepackers get their heavy Tour Divide rigs up all the hills from Banff to Antelope Wells.

Pricing

As you'd expect from a fully wireless electronic drivetrain, none of this comes cheap. However, given the backwards compatibility with previous generations of components, those upgrading can expect to find some savings by keeping some of their existing components. Eschewing buttons on the left side brifter also saves 250 USD, should you choose to go that route - given there's three buttons on the right side, you should be able to find a configuration that works.

Setup/installation

Installation of GRX is a familiar procedure that anyone with a modicum of experience on hydraulic brifters and Shimano derailleurs will be capable of. My T47 bottom bracket required an aftermarket solution as Shimano doesn't make one, but otherwise it was straightforward to get everything hung and bled. Then, it was on to electronics.

I made no secret of the fact that I didn't get along with Shimano's app - E-Tube Project Cyclists - in my previous electronic GRX review. This is still true, I find it frustratingly slow and not a great user experience. I believe it's a product of a culture I see in many aspects of Shimano's products - it's deeply ingrained in the company that the solution is whatever the engineering department decides; how else do you defend the continued use of cup-and-cone hubs other than a data deep-dive on energy and watts. But cup-and-cone hubs suffer from the same issue that ultimately killed the previous mountain derailleur clutches; while they were a great solution on paper, without proper maintenance, performance degraded. And the average consumer isn't adjusting hubs, or derailleur clutches. Sometimes, the quantitatively 'correct' engineering solution isn't the best one for the real world.

With that said, there's no arguing that E-Tube provides a deep level of customization and options that aren't available in other electronic drivetrain ecosystems. Unlike some competitors, using the app is also required for setup and initial pairing of components, using a combination of physical buttons on the components and QR codes. Firmware updates to the derailleur are possible, however updates to the brifters require a shop to plug in with cables. I connected to the new derailleur, paired up my brifters, and it was on to setup. While my b-tension and limit screw adjustment muscles haven't been used in some time, decades of muscle memory meant I was on to trimming the derailleur inside E-Tube, and on the groad, in short order with some baseline control settings.

Riding Impressions

I've got about 200 kilometers on the group so far, so consider these impressions preliminary. I think one of the most interesting things is how "Shimano shifting" this feels - despite being controlled by electromagnetic waves travelling through the air. Shifts feel distinctly different from SRAM's gravel-specific Force XPLR kit it replaced on my bike. It's hard to describe - but it's almost a more delicate feeling, like the derailleur is gently coaxing the chain into the desired position instead of mandating it. The result of this is a more traditional feeling drivetrain, where backing off the power momentarily yields improvements in shift quality. To try and explain, this is the opposite of SRAM's mountain T-Type drivetrains which practically rewards high-load shifting. I've heard Linkglide is similar, although I have no personal experience with Linkglide.

The system takes slightly longer to wake up than SRAM - Shimano says this is an effort to increase battery life, especially in transport. In practice, a couple of quick clicks as you hop on make this a non-issue.

Shift quality isn't as high as I was expecting, and in an effort to improve it, I've slowed down shift speed in E-Tube, from 'normal' to 'slow'; I can't tell if it's placebo, but I think I'm experiencing crunchy downshifts less often now, although my 3->2 shift is still regularly bad. Upshifting isn't quite as smooth as I'd like, with the occasional ka-CHUNK of yore, as the chain hops down to the smaller cog. I'm hoping that a bit of tuning and tweaking can improve things, and I'm going to continue to play with both the mechanical and electronic ends of the gruppo to see if I can dial everything in.

There's an obvious sacrifice in 1x12; gear resolution. Depending on your use case, this matters or it doesn't. As a general rule, it's only on smooth gravel or tarmac I find myself hunting for gears if I'm solo; if you're regularly in groups it can exacerbate the issue, but this is a choice, and if you want more resolution there are other options.

Navigating the SKUs

The real story here - perhaps - isn't that Shimano now sells a wireless derailleur that says GRX on it, but that Shimano now has a full ecosystem of wireless components that gravel and all-road riders can pick and choose from to find their ideal setup. It's all backwards compatible as well, enabling folks to use existing cranksets, cassettes, and in some cases retaining brifters, depending on your specific current configuration. There's a huge amount of new and old components that work together now, which is good for those that like to play bicycle LEGO.

If I were assembling a group myself, I'd probably be going with an XT mid-cage derailleur paired with an XT 10-45 cassette; sacrificing a bit of overall gear range for improved gear resolution. If cost is no object, I'll have a spare long cage derailleur and 10-51 cassette for trips that make gear range trump resolution. Alternatively, you could keep the mid-cage derailleur and swap cassettes for the XT 9-45. If you're looking for a lower gear with this arrangement, you'd also need to change front rings (and likely chain). The pauper version is a smaller front ring and spare chain, giving up top-end.

The first option is effectively what I run now as my personal setup, with a 10-46 Force XPLR mated to a 42T front ring most of the time, and a 10-52 XO1 and GX T-type quickly poached off a mountain bike for big, heavy trips. I'm able to do this on the same chain, which is convenient, and the swap takes about 5 minutes.

I'd pair these XT bits with an ST-RX825-R brifter for shifting control, and a ST-RX810-LA brifter on the left. While designed for 2x bikes, this component can also control a cable-actuated dropper post, and as Mike discussed yesterday I love having a dropper post on my gravel bike. While both Shimano and Fox are tight-lipped about any future development or compatibility between their wireless components, for consumer's sake I hope they can forge some kind of technology agreement, because my dropper is what I'm missing most at the moment.

For cranks, I'm not sure exactly what I'd do. While I use a 172.5mm length and 42T ring, I'm accustomed to a powermeter and there's no official Shimano way to get that combo, short of aftermarket chainrings on a Dura-ace or Ultegra crankset.

Overall the new GRX brings mullet gravel drivetrains to the Shimanophiles, and once everything was set up, riding this setup has been very similar to the Specialized Diverge I reviewed and raced in the BCBR Gravel Explorer XLT.

Given Shimano's history I don't have any particular longevity concerns, especially with components built for mountain bike abuse. I'm hoping I can tune the shifting to improve a bit, and tame the shifter rattle; I'll be keeping this for long-term review, so stay tuned in for an update in a few months.