More than one year ago, Shimano released new, 12 speed GRX components. This was expected, but what wasn't expected was that the Di2 electronic shifting version would only come in a 2x, (double chainring) version. The much-wanted electronic shifting 1x GRX 12 speed Di2 components designed around a single chainring were missing in action, a strange oversight.
The wait is over, however, and as of June 2025 there are now new 1x-specific versions of the Di2 components of Shimano's 12 speed GRX group. Let's take a look at the new components, as well as review which stay the same (like the crankset).
What you need to know about the GRX 1x Di2 rear derailleur
Here's the short summary of the new GRX Di2 1x rear dearailleur:
- It's fully wireless. Unlike the current Dura-Ace / Ultegra road groups, there is no wire connecting the rear derailleur to an internal seatpost battery. Instead, the battery is integral to the rear derailleur, following the pattern set by the mountain bike XTR group released in Spring 2025.
- The new RD-RX827 rear derailleur is more like an MTB derailleur than a road derailleur, picking up off-road features like a skid plate and "Shadow ES" low profile design
- It also includes an "automatic impact recovery" feature, which claims to reset the derailleur in the event of impact, like with a rock. This could be very useful for cyclocross, where we have seen Di2 derailleurs crippled by impact in the past.
- the RD-RX827 handles big, 10-51 cassettes
- the new RD-RX827 removes the manual on/off clutch feature found on some previous Shimano designs, and is replaced by an "always-on" spring setup instead.
There's a new shifter, also
The GRX Di2 shifters are mostly unchanged, however, there's now a 1x-only option, saving some weight since there are no left side shifter electronics needed to operate a front derailleur.
How about that crankset?
The venerable GRX crankset stays the same, which is good, because there's nothing wrong with it. It's aluminum, durable, pretty lightweight, not too expensive, and reliable. This component has had quite the lifespan, also staying essentially unchanged during the transition from GRX 11 speed to 12 speed - even though it received a new model number it's really identical.
The crank comes in the same 40 and 42 teeth chainring options as it did before, and since this is a very popular model, there are plenty of 3rd party chainrings available that fit it, such as those from Wolf Tooth and other brands.
The new GRX Di2 12 speed wireless is ideal for older bikes
Why, you say? Well, modern bikes that were designed for electronic shifting featured slick integrated ports to hide the wiring inside the frame tubes. Older bikes that pre-dated electronic shifting's popularity could be retrofitted with electronic drivetrains, but would often have wires zip-tied outside the frame tubes, which is not only ugly, but leads to snagging.
Since the new 1x GRX 12 speed kit is fully wireless, there's no wire to hide inside the frame tubes or snag on anything - easy to retrofit, even to older bikes.
Another reason GRX is a good match for older bikes - unlike SRAM's "Transmission" style components, GRX doesn't require an updated, modern frame design, any old "classic" type derailleur hanger will do. If you're feeling shut out because your older frame wasn't designed for Transmission, GRX might be for you.
Battery life
Claimed battery life of the new GRX 12 speed Di2 1x setup is 1000 kilometers (620 miles) - that's good enough for multi-day bike packing adventures, long training weeks, and so on.
For reference, I have a reminder to charge my 12 speed Di2 Ultegra-equipped road bike set on my calendar to fire off monthly. Sometimes the automatic battery life reminders that popup on your Garmin or similar head unit don't provide quite enough advance notice, so I prefer to set a manual reminder, and will likely do the same for a GRX 12 speed Di2 bike as well.
Shimano GRX 12 speed Di2 1x limitations and downsides
While GRX 12 speed Di2 1x largely seems like a win, and was widely wanted/anticipated, it does come with some downsides:
- While it can technically be used with a "classic" HG free hub rear wheel, it really needs Microspline (more on that below) which might mean many riders need new wheels, too.
- There's no power meter option. While Shimano does have their own power meter intended for road (Dura-Ace, Ultegra) applications, it doesn't have the best reviews, and won't work for GRX applications. That leaves 3rd parties to fill the void for GRX... options include the 4iiii Innovations and Stages models. If crank-based power meters aren't for you, pedal-based power meters are always an option too.
- With short cranks all the rage these days, note the higher-end GRX RX820 option doesn't include a 165mm option for shorter riders.
A word about Microspline
Unlike the prior GRX 11 speed mechanical and Di2 groups, it's worth noting that the 12 speed version of GRX is built around Shimano's Microspline freehub body. While many wheels offer the ability to change out the freehub body to accomodate, some don't - for example, I own a set of Zipp 303s wheels, which sadly, aren't convertible.
I might experiment with using a 12 speed cassette with an HG freehub instead - but that precludes the use of all the wide-range 12 speed mountain bike cassettes that were intended for use with GRX. With HG 12 speed cassettes, the 10 tooth small cog isn't available, and from what I can find, the large cog maxes out at 36 teeth. That's unsuitable for steep off-road riding with 1x setups, and not a great compromise.
So if you really want to use the Shimano GRX 12 speed Di2 group in a 1x setup, you'll need a Microspline rear wheel to match - without it, your cassette and gear range choices are severely limited.