GRX Di2 goes semi-wireless
Shimano has announced the release of GRX Di2 RX825 – its long-awaited 12-speed electronic gravel bike groupset.
GRX Di2 RX825 adopts the same semi-wireless design first introduced on Shimano’s road-specific Di2 groupsets, with a set of wireless shifters paired to semi-wireless front and rear derailleurs.
The derailleurs are then wired to, and powered by, Shimano’s standard separate Di2 battery.
The rest of the GRX Di2 RX825 groupset is made up of existing 12-speed components from Shimano’s GRX RX820 mechanical groupset and its range of electronic road groupsets.
Unlike the original GRX Di2 RX815 groupset, GRX Di2 RX825 will only be offered in 2x (‘Undroppable’, as Shimano refers to it) configurations at launch.
Shimano has confirmed 1x GRX Di2 RX825 “is coming”, but it declined to offer a specific timeline for this.
Shimano has also announced a new shifting mode called Front Shift Next, for GRX Di2 RX825 and its 12-speed Di2 road groupsets. This enbles users to designate any Di2 shifter button to actuate a front shift (in either direction) when pressed.
A limited-edition GRX pedal set is also available, which takes a Deore XT SPD pedal set and adds ‘United in Gravel’ graphics.
Simon von Bromley has weighed every component of new GRX Di2 RX825 and you can read up on his findings here.
Shimano GRX Di2 RX825 | What you need to know
- Shimano’s first 12-speed electronic gravel bike groupset
- 2x-only at launch, with 1x groupsets coming later
- New wireless shifters with updated ergonomics
- Semi-wireless front and rear derailleurs
- Two cassette options – 11-34 and 11-36t
- Two chainring set options – 48/31 and 46/30t
- New Front Shift Next customisable Di2 button functionality
- Limited-edition GRX pedal set
Semi-wireless, 12-speed GRX Di2
Like GRX RX820 – Shimano’s 12-speed mechanical gravel bike groupset – GRX Di2 RX825 is pitched at the same ‘level’ as Shimano’s Ultegra Di2 R8100 and Deore XT M8100 groupsets.
As things stand, then, there’s still no GRX-equivalent for Shimano’s flagship road and mountain bike groupsets, Dura-Ace Di2 R9200 and XTR M9100.
When we put this to Shimano, it said it is focused on supporting its “biggest group of riders first”, and while it didn’t rule out producing high-end GRX components, it also declined to confirm whether it had plans to do so.
Compared to the original, 11-speed GRX Di2 RX815 groupset, the key changes with GRX Di2 RX825 are the move to wireless shifters and the adoption of 12-speed, semi-wireless front and rear derailleurs.
As with Shimano’s 12-speed road bike rear derailleurs, the new GRX Di2 RD-RX825 rear derailleur houses the ‘brains’ of the groupset, eliminating the need for a dedicated junction box elsewhere in the setup.
Shimano says the GRX Di2 RD-RX825 rear derailleur uses the same electronics as the latest Dura-Ace Di2 RD-R9250 rear derailleur, however it doesn’t claim it has the same, 58 per cent faster shifting speed as that.
In fact, Shimano isn’t making any specific claims surrounding improvements to shifting performance with the entire GRX Di2 RX825 groupset.
Shifting aside, though, the groupset sees a number of refinements, including a tweak to the shifter ergonomics and a slight expansion to available gearing range.
As noted, GRX Di2 RX825 will only be available in 2x configuration at launch, although Shimano has confirmed a 1x 12-speed GRX Di2 groupset is in development (more on this later).
Shimano GRX Di2 ST-RX825 shifters
Like Shimano’s latest-generation Di2 road shifters (or ‘dual control levers’, as Shimano calls them), the GRX Di2 ST-RX825 shifters move to a wireless design.
This means there are no more Di2 wires running from the shifters to the central Di2 battery housed within the frame. Instead, each shifter is powered by a set of two CR1632 batteries. Shimano claims these should last for around three-and-a-half to four years.
The move to a wireless design helps tidy up the front end and eases installation, especially as gravel bikes become ever more integrated. Of course, there are still brake hoses to route – like its mechanical equivalent, GRX Di2 RX825 is only compatible with hydraulic disc brakes.
As well as being wireless, the new GRX Di2 shifters feature updated ergonomics and improved compatibility with flared gravel bike handlebars.
The overall shape and design is similar to the outgoing 11-speed GRX Di2 ST-RX815 shifters, although Shimano notes the new shifters are rounder.
The shifter buttons layout is the same, with two buttons on the outside of either brake lever, plus an additional customisable auxiliary button on the inside of each shifter hood.
The ST-RX825 shifters also include wire ports for Shimano’s SW-RS801-T satellite shifters (available separately).
Shimano has also announced a new customisation option called ‘Front Shift Next’, which enables any single button to be assigned to actuate a front shift in either direction (more on this later).
As with the latest 12-speed mechanical GRX shifters, Shimano says the new 12-speed GRX Di2 shifters are better optimised for use on flared handlebars. It also claims the transition point between the hoods and handlebar has been improved to lessen the risk of pressure points.
The brake levers also get the same anti-slip coating designed to improve grip and braking confidence in wet conditions. According to my colleague Liam Cahill, who attended the mechanical GRX launch, this tech has been borrowed from Shimano’s fishing rods and reels.
The claimed weight for a set of Shimano GRX Di2 ST-RX825 shifters is 415g.
That’s up 42g compared to the previous generation shifters (which were claimed to weigh 373g per set), though ditching the junction box and additional wires should help even things out.
Shimano GRX Di2 RD-RX825 rear derailleur
The new GRX Di2 RD-RX825 rear derailleur is now 12-speed and contains the brains of the new GRX Di2 groupset, wireless connectivity and the charging port.
As with Shimano’s 12-speed road bike electronic groupsets, this negates the need for a separate junction box elsewhere in the system.
Its wireless connectivity also enables it to communicate with the new ST-RX825 shifters, as well as compatible bike computers and smartphones running Shimano’s E-Tube Project app.
Despite this, the new RD-RX825 rear derailleur remains impressively svelte – partly thanks to the fact it’s wired to, and powered by, a central internal battery (typically housed within the bike’s frame or seatpost).
In contrast, SRAM’s AXS and Campagnolo’s Super Record Wireless derailleurs are a little bulkier because each carries its own detachable battery.
There’s just a single cage length available for the GRX Di2 RX825 rear derailleur, but where previous 2x GRX Di2 had a maximum cassette size of 34t, the new one can shift up to a 36t sprocket.
As with 2x mechanical GRX RX820, cassette options for GRX Di2 RX825 start with an 11t cog.
Shimano’s 12-speed 1x mechanical GRX groupsets use cassettes starting with a 10t sprocket, though, and we expect that to be adopted whenever a 12-speed 1x GRX Di2 groupset becomes available.
As before, the GRX Di2 RD-RX825 rear derailleur uses Shimano’s Shadow Plus clutch to help keep the chain in check while riding on rough terrain.
It also receives a small aesthetic update, with a more uniform, dark grey colour similar to that of Shimano’s Ultegra Di2 R8100 groupset.
Sadly, the polished silver finish seen on GRX Limited is nowhere to be seen.
Claimed weight for the GRX Di2 RD-RX825 rear derailleur is 310g – an increase of 23g from the 287g claimed for the previous 11-speed version.
Shimano GRX Di2 FD-RX825-F front derailleur
The new 12-speed GRX Di2 front derailleur features a reprofiled cage alongside a slightly updated main body.
As before, it’s designed to work with chainrings up to 48t (if you need larger chainrings, you can use a 105, Ultegra or Dura-Ace Di2 front derailleur) and has a total capacity (the difference in tooth count between your two chainrings) of 17t.
The chainline is also 2.5mm wider, compared to a road bike front derailleur, to help improve tyre clearance (useful because the best gravel bike tyres keep getting wider).
Notably, the new 12-speed GRX Di2 front derailleur doesn’t benefit from the smaller form factor afforded to Shimano’s latest Ultegra and Dura-Ace Di2 groupsets (which are both 33 per cent smaller than the previous versions).
Instead, the GRX Di2 FD-RX825 front derailleur looks more akin to the one found on Shimano’s 105 Di2 R7100 groupset.
This matters because Shimano claims the latest Ultegra and Dura-Ace Di2 front derailleurs also benefit from smaller and more powerful motor systems that boost front shifting speed by a claimed 45 per cent.
In contrast, the 105 Di2 R7100 front derailleur uses the bulkier motor system from the previous-generation Ultegra Di2 R8000 and Dura-Ace Di2 R9100 groupsets. Consequently, it doesn’t benefit from the improved shifting speed offered by Shimano’s pricier road groupsets.
Shimano’s press release likewise doesn’t claim any specific performance improvements for front shifting compared to 11-speed GRX Di2.
When we put this to Shimano, however, it said the GRX Di2 front derailleur uses a stronger motor than its road-specific equivalents, due to the more challenging circumstances it operates in.
It also confirmed there have been internal design changes for the new GRX Di2 RX825 front derailleur, though it declined to say whether these result in any improvements to performance.
Shimano’s claimed weight for the GRX Di2 FD-RX825 front derailleur is 142g, up 7g from the previous version (135g).
Everything else
The rest of the 12-speed GRX Di2 RX825 groupset is made up of existing Shimano components.
That includes the FC-RX820-2 crankset, which features 48/31t chainrings, or the FC-RX610-2 crankset with 46/30t chainrings.
Both cranksets have a 151mm Q-Factor and there are only three crank lengths available – 170, 172.5 and 175mm. In contrast, Shimano’s Ultegra R8100 road crankset is available in five lengths, from 160 to 175mm.
There are two cassette choices – an Ultegra-level CS-R8101-12, 11-34t option or the wider CS-HG710-12, 11-36t cassette introduced with Shimano 105 Di2. Both are compatible with HG and HG+ freehubs.
The brakes are the same BR-RX820 calipers as used on mechanical 12-speed GRX. These feature 10 per cent greater pad clearance, an updated bleed port location and Shimano’s Servo Wave technology.
The rotors are Shimano’s latest RT-CL800 model, which have a “more robust” carrier and redesigned braking surface. These are designed to reduce deformation and fade under sustained, heavy braking, leading to quieter and more consistent performance.
The chain is the 12-speed, Ultegra / XT level, CN-M8100 model.
The BT-DN300 Di2 battery, EW-SD300 wires and EW-EC300 charging cable are all adopted from Shimano’s latest 12-speed electronic road bike groupsets.
This means the new 12-speed GRX Di2 components are not backwards compatible with older 11-speed parts, such as the BT-DN110-A battery, EW-SD50 wires or SM-BCR2 charger.
Why no 1x?
At this time, Shimano is only launching 12-speed GRX Di2 as a 2x groupset.
When asked, Shimano did confirm “1x is coming”, but declined to put a date on when it might arrive.
If we were to speculate, we suspect – given the similarity between Shimano’s 1x 12-speed GRX components and those from its mountain bike groupsets – it might launch concurrently with a new range of 12-speed electronic mountain bike groupsets.
We don’t know when – or even if – that will happen, of course. Given we haven’t seen a new Di2 MTB groupset since 2016, when XT M8050 Di2 launched, though, it surely can’t be too far away now.
What about power meters?
A 1x iteration arguably isn’t the only thing missing, however – there’s still no native power meter option for GRX either.
While SRAM now offers power meters at every level of its wireless AXS groupsets, Shimano has yet to port over the power measurement technology from its Dura-Ace and Ultegra road bike cranksets.
When asked if it had any plans to introduce a GRX power meter crankset, Shimano said it couldn’t “speculate on future product developments”, but that it would consider doing so if there was appropriate demand.
It’s likely there will be third-party options from the likes of 4iiii (Stages sadly ceased operations amid financial difficulties in recent weeks, according to reports from numerous sources), though. Alternatively, riders could use power meter pedals, such as Favero’s Assioma Pro MX, Garmin’s Rally XC200 or Look’s new X-Track Power.
Shimano GRX Di2 RX825 claimed weights and pricing
Weights
Adding everything up gives a claimed total weight of 2,747g for a complete groupset, excluding wires and brake hoses.
That’s a little heavier than its 11-speed predecessor, which had a claimed weight of 2,679g in a comparable spec.
However, given the 11-speed groupset uses more wires, the real-world difference between the two groupsets may be smaller.
| Shimano GRX Di2 RX825 (12-speed) | Claimed weight (grams) | Shimano GRX Di2 RX815 (11-speed) | Claimed weight (grams) |
|---|---|---|---|
| ST-RX825 shifters | 415 | ST-RX815 shifters (pair) | 373 |
| RD-RX825 rear derailleur | 310 | RD-RX815 rear derailleur | 287 |
| FD-RX825-F front derailleur | 142 | FD-RX815-F front derailleur | 135 |
| FC-RX820-2 crankset (48/31t, 172.5mm) | 721 | FC-RX810-2 crankset (48/31t / 172.5mm) | 710 |
| CS-R8101-12 cassette (11-34t) | 345 | CS-HG800-11 cassette (11-34t) | 335 |
| BR-RX820 calipers (front and rear, including hose and fluid)) | 282 | BR-RX810 calipers (front and rear, excluding hoses and brake fluid) | 265 |
| RT-CL800 (160mm pair) | 228 | SM-RT800 rotors (160m, pair) | 256 |
| CN-M8100 chain (126 links) | 252 | CN-HG701-11 chain (114 links) | 257 |
| BT-DN300 battery | 52 | BT-DN110-A battery | 50 |
| EW-RS910 junction box | 11 | ||
| Total | 2747 | Total | 2679 |
In terms of actual weights, the complete GRX Di2 RX825 groupset weighs 2,892g on our scales. That figure includes small parts such as brake hoses and fluid, Di2 wires, rotor lockrings and the mounting parts for the Di2 battery.
Our test groupset also differs slightly from the standard spec, with a set of the older RT-MT900 brake rotors plus the wider-range (and lower tier) 11-36t CS-HG710-12 cassette.
Our crankset also has 170mm cranks, whereas Shimano offers its claimed weight for a 172.5mm version.
For a full breakdown of every part, though, click through to see our actual weights and first impressions of Shimano’s new GRX Di2 RX825 groupset.
Pricing
| Shimano GRX Di2 RX825 | Price (£) | Price ($) |
|---|---|---|
| ST-RX825 shifters and BR-RX820 brakes | 799.98 | 1113.98 |
| RD-RX825 rear derailleur | 324.99 | 409.99 |
| FD-RX825-F front derailleur | 184.99 | 209.99 |
| FC-RX820-2 crankset (48/31t / 172.5mm) | 229.99 | 249.99 |
| CS-R8101-12 cassette (11-34t) | 119.99 | 164.99 |
| RT-CL800 rotors (160m, pair) | 109.98 | 111.98 |
| CN-M8100 chain (126 links) | 49.99 | 75 |
| BT-DN300 battery | 174.99 | 184.99 |
| EW-SD300 (750 and 1000mm) | 57.98 | 60 |
| EW-EC300 charging cable | 44.99 | 49.99 |
| Total | 2097.87 | 2630.9 |
In terms of pricing, the individual component prices for GRX Di2 RX825 have gone up compared to their 11-speed equivalents.
However, at approximately £2,100 / $2,631 / €2,479, the total price for the GRX Di2 RX825 groupset is similar to the previous 11-speed version.
This is because you don’t need as many wires, connectors or a junction box, and the latest Di2 charging cable is also significantly cheaper than the old version.
The exact price will depend on the configuration of the groupset you choose and, as always, real-world prices may vary.
Front Shift Next
As part of the GRX Di2 RX825 launch, Shimano is also unveiling a new shifting logic option called ‘Front Shift Next’.
This enables riders with 12-speed Di2 drivetrains to assign any shifter button in the system to actuate a front shift.
Pressing this button then prompts the front derailleur to shift up or down, depending on what chainring you’re using when you press the button.
According to Shimano, Front Shift Next is designed to simplify its Di2 shifting logic for “less-experienced riders” and offer a one-button front shifting option for experienced riders.
By assigning front shifting to a single button, Front Shift Next can also help free up an additional Di2 button for other tasks, such as controlling a compatible bike computer or lights.
Shimano says Front Shift Next can be set up on GRX Di2 RX825 and all three of its 12-speed Di2 road bike groupsets, via its E-Tube Project app for smartphones.
Limited-edition GRX pedals
Last but not least, Shimano is also debuting a new set of limited-edition GRX gravel pedals.
Shimano says the GRX SPD M8100-UG pedal is a “celebration of gravel cycling”, thanks to some snazzy new ‘United in Gravel’ graphics.
Essentially, these appear to be Deore XT PD-M8100 pedals with some updated graphics, but perhaps that’s no bad thing – in our experience, those are great off-road pedals.
The GRX SPD M8100-UG pedals are compatible with Shimano’s SPD cleats and compatible shoes (Shimano naturally recommends its own gravel shoes, such as the RX8 or RX6), and offers dual-sided entry and exit.
The claimed weight for a set of GRX SPD M8100-UG pedals is 342g – exactly the same as the standard Deore XT version.
They are priced at £114.99 / €109.99.