We take an in-depth look at Shimano’s latest electronic gravel groupset
Shimano’s 12-speed GRX Di2 RX825 is finally here and we’ve got our hands on a full groupset.
In this article, we’re going to weigh every component and compare it to Shimano’s claimed figures.
We’ll also give you our first impressions on Shimano’s new flagship gravel bike groupset.
Unusually, Shimano’s press release doesn’t make any reference to the overall weight of the new GRX Di2 RX825 groupset – could it have gained weight compared to the outgoing 11-speed GRX Di2 RX815 groupset? Let’s find out.
If you want more information on the launch of Shimano GRX Di2 RX825, head over to our news story.
Shimano GRX Di2 RX825: a primer
- GRX Di2 RX825 is Shimano’s first 12-speed electronic gravel bike groupset
- It’s 2x-only at launch, with 1x groupsets coming at a later (unspecified) date
- It adopts the semi-wireless design of Shimano’s 12-speed electronic road bike groupsets, with wireless shifters and semi-wireless front and rear derailleurs
- Pitched at roughly the same level as Shimano’s Ultegra Di2 R8100 and Deore XT M8100
- There are two cassette options – 11-34 and 11-36t – plus two chainring set options – 48/31 and 46/30t
Shimano GRX Di2 RX825 groupset components first impressions and real weights
Shimano GRX Di2 ST-RX825 shifter weight
The big update for the GRX Di2 ST-RX825 shifters is the move to a wireless design.
As on Shimano’s 12-speed road Di2 groupsets – Dura-Ace Di2 R9200, Ultegra Di2 R8100 and 105 Di2 R7100 – this means there are no longer any wires running from the shifters to the Di2 battery (which still powers the derailleurs – more on this later).
Instead, each shifter is powered by a pair of CR1632 coin cell batteries. According to Shimano, these should last around three-and-a-half to four years – depending on how much you use your shifters.
There are still hoses for hydraulic disc brakes to consider, of course (Shimano’s patent for electric braking remains just an idea for now), but removing the Di2 wires should go some way to making installation easier on today’s increasingly integrated gravel bikes.
Ergonomically, it’s evolution not revolution – which will be welcome news to the many who liked the previous-generation shifter shape.
Rather than adopting the new shifter shape seen on Shimano’s 12-speed electronic road groupsets, Shimano has instead lightly updated the shape carried over from 11-speed GRX Di2 RX815.
Overall, the new shifters are slightly rounder on top, while Shimano says they’re also better optimised for use on flared gravel handlebars.
The claimed weight for a set of GRX Di2 ST-RX825 shifters is 415g – 42g more than the 11-speed ones.
On our scales, though, our set of test levers weighed a bit more, at 440g. It’s possible, then, that Shimano’s claimed weights may not account for hydraulic brake fluid (mineral oil, in this case).
- Claimed weight: 415g
- Actual weight: 440g
Shimano GRX Di2 RD-RX825 rear derailleur weight
As part of the move to a semi-wireless setup, the new GRX Di2 RD-RX825 rear derailleur takes on the role of the groupset’s ‘brain’. This negates the need for a separate Di2 junction box elsewhere in the system.
The charging port has also been relocated to the rear derailleur, as has the groupset’s wireless connectivity.
As with its 11-speed predecessor, the 12-speed GRX Di2 rear derailleur remains wired to a central Di2 battery, typically housed in the bike’s seatpost or seat tube.
This enables it to retain an impressively svelte design, though of course it means whoever’s installing it will need to do some internal cable routing when setting it up.
There’s a single cage length available, although it’s not rated for cassette sprockets up to 36 teeth (up from 34t on the previous version), giving riders a touch more range at the low end.
Looks-wise, it’s a case of continuity again, with only a small aesthetic change compared to the previous generation.
The 11-speed GRX Di2 RD-RX815 rear derailleur used a two-tone grey finish, with an embossed GRX logo attached to a hollow outer parallelogram plate.
In contrast, the 12-speed RD-RX825 rear derailleur uses a monotone, dark grey finish, with a solid outer parallelogram plate and a painted logo. This is more in line with the finish on Shimano’s latest Ultegra Di2 R8100 groupset.
Is it an improvement? Aesthetics are subjective, of course, but it’s not the most exciting finish.
Personally, I’m disappointed the design wasn’t influenced more by Shimano’s polished silver GRX Limited groupset.
In terms of performance, Shimano isn’t claiming any specific improvements to shifting speed or accuracy.
It did tell us that the new GRX Di2 RX-RX825 rear derailleur has been redesigned with the electronics from the Dura-Ace Di2 R9200 rear derailleur, but whereas that launched with stated 58 per cent faster shifting, Shimano isn’t making any such claims here.
Shimano’s claimed weight for the GRX Di2 RD-RX825 rear derailleur is 310g – up 23g compared to the previous version – and our sample weighed exactly that.
- Claimed weight: 310g
- Actual weight: 310g
Shimano GRX Di2 FD-RX825-F front derailleur weight
The GRX Di2 FD-RX825 front derailleur appears visually similar to the outgoing, 11-speed version.
Likewise, its specs are almost identical, with a maximum chainring size of 48t and a capacity (the maximum teeth difference between your two chainrings) of 17t.
This means it doesn’t get the 33 per cent smaller form factor of Shimano’s latest Dura-Ace and Ultegra Di2 front derailleurs, and perhaps not the claimed 45 per cent faster shifting either.
Despite this, Shimano says there have been internal changes for this latest 12-speed version, as well as changes to the profile of the cage.
It declined to say if these changes result in any improvements to front shifting, but it noted its GRX Di2 front derailleur uses “stronger” motors than its road equivalents to deal with the more challenging nature of gravel riding.
Shimano’s claimed weight for the GRX Di2 FD-RX825-F front derailleur is 142g – 7g more than the outgoing version. On our scales, it weighed a little less, at 139g, though.
- Claimed weight: 142g
- Actual weight: 139g
Shimano GRX FC-RX820 crankset weight
The GRX FC-RX820 crankset is a direct carry-over from the 12-speed GRX RX820 mechanical groupset.
The twin Bolt Circle Diameters of 110×4 and 80×4 are also carried over.
In terms of crank lengths, it’s still only 170, 172.5 and 175mm lengths available. With many riders opting for shorter cranks nowadays, it’s surprising to see such little choice available at this level.
In contrast, Shimano’s Ultegra R8100 road crankset is available in five lengths from 160 to 175mm.
The chainrings have seen more of a change, though, with updated tooth profiles optimised for 12-speed chains and more cut-outs on the big chainring to save weight.
Given my experience of running 11-speed Shimano chainrings with 12-speed Shimano chains, if you have an older 11-speed GRX crankset it will likely work just fine with this new groupset.
Alternatively, you could just buy the new 12-speed chainrings because the cranks themselves appear to be identical to those from the 11-speed GRX groupsets – FC-RX810/RX820 (FC-RX810 is Shimano product code for its 11-speed GRX cranks) is even printed on the reverse of the driveside crank arm.
It still uses the same all-black paintjob too. This matches the new dark grey derailleurs a little better than before, but it’s still slightly frustrating the crankset isn’t styled to match the derailleurs perfectly, as on Shimano’s other high-end groupsets.
Of course, once everything’s covered in dust and mud, it arguably doesn’t make a difference.
Still though, it doesn’t feel unreasonable to expect a £2,100 / $2,575 / €2,479 groupset to be aesthetically cohesive.
In terms of weight, Shimano says a 172.5mm GRX FC-RX820 crankset with 48/31t chainrings weighs 721g.
On our scales, our 170mm crankset with the same chainrings weighs 710g.
- Claimed weight: 721g
- Actual weight: 710g
Shimano GRX BR-RX820 brake calipers and hoses weight
Like the crankset, the GRX RX820 brake calipers and hoses are straight ports from the latest mechanical groupset.
The key upgrades compared to the previous-generation RX810 calipers include 10 per cent greater pad clearance, for reduced brake rub, and a new bleed port location for easier maintenance.
Our set includes Shimano’s L05A-RF resin disc brake pads, although you could swap these out for its L04C-MF metal pads if you want something that lasts a little longer in muddy or sandy conditions.
Notably, though, Shimano claims its latest brake pads last up to 50 per cent longer than the previous-generation L03A pads, and up to 110 per cent longer than the L02A pads.
Shimano’s claimed weight for a set of front and rear GRX BR-RX820 brake calipers is 282g, though this must not include hoses because our set comes in at 335g (including hoses and presumably some brake fluid).
- Claimed weight: 282g
- Actual weight: 335g
Shimano CS-HG710-12 cassette, 11-36t weight
2x GRX Di2 officially has two cassette options, an Ultegra-level, 11-34t cassette or a slightly wider, 105-level 11-36t option.
We’ve got the second option – the CS-HG710-12 cassette, to give it its full name.
As well as being slightly heavier, thanks to its less aggressive use of drillium and simpler construction, it also doesn’t get Shimano’s latest Hyperglide+ tooth profiling (which features on Ultegra and Dura-Ace cassettes).
Instead, it makes do with Shimano’s ‘standard’ Hyperglide tooth profiles.
In our experience, this tends to mean slightly louder running and shifts that are marginally less smooth, although we’ll reserve judgement until we’ve been able to test this groupset properly, of course.
Shimano doesn’t offer a claimed weight for the CS-HG710-12 cassette, but on our scales it weighed 381g.
That’s up 46g compared to the claimed weight for the Ultegra-level 11-34t CS-HG800-11 cassette specced with the outgoing groupset, although that’s a slightly unfair comparison given the CS-HG710-12 cassette is both wider-ranging and part of a lower-tier groupset.
The 12-speed, 11-34t CS-R8101-12 cassette is claimed to weigh a more comparable 345g.
Of course, if you’re looking for smoother shifting and even lower weight than the Ultegra cassette, you can use an 11-34t Dura-Ace R9200 cassette with the new GRX Di2 groupset too. The only thing it would cost you is more money.
- Claimed weight: Not given
- Actual weight: 381g
Shimano RT-MT900 brake rotors and lockrings weight
The brake rotors for the new 12-speed GRX Di2 are supposed to be the latest Ultegra / Deore XT-level RT-CL800 model, however our test groupset shipped with a set of previous-generation, Dura-Ace / XTR-level RT-MT900 rotors.
Supply of bike parts has improved immeasurably in recent months, but it seems some supply-chain issues may still be lingering within the industry.
In our experience, the RT-MT900 (and Ultegra-level RT-MT800) rotors offer a significant step up in performance compared to the original SM-RT800 rotors (which were very noisy in wet conditions), but the latest RT-CL800 rotors are even better.
Primarily, we’ve found they deform less under heavy braking and tend to be even quieter in wet weather.
Still, though, it’s a small detail overall and shouldn’t affect our ability to properly test the groupset.
Our set comprises one 140mm rotor and a larger 160mm rotor.
Most gravel bikes are typically specced with a 160mm pair nowadays, for improved braking power and durability, but again, we’ll no doubt be able to make do with what we have.
Shimano’s claimed weight for the pair is 196g, though our set weighs 216g including the lockrings.
For reference, the claimed weight for a 160mm set of specification-correct RT-CL800 rotors is 228g.
- Claimed weight: 196g
- Actual weight: 216g
Shimano CN-M8100 XT/Ultegra chain with quick-link weight
The CN-M8100 XT/Ultegra chain is exactly the same as found on Shimano’s latest Ultegra and Deore XT groupsets.
There’s not much to say about it other than the fact it’s 12-speed and is claimed to weigh around 10g more than a 12-speed Dura-Ace / XTR chain.
It gets Shimano’s Sil-Tec treatment, though, which is a fluorine-based plating claimed to reduce friction and drivetrain noise, and improve durability.
Shimano’s claimed weight for the CN-M8100 XT/Ultegra chain is 252g, but our sample weighs 283g including the quick-link.
- Claimed weight: 252g
- Actual weight: 283g
Shimano BT-DN300 battery and EW-SD300 wires weight
The BT-DN300 battery and EX-SD300 wires are also carried over from Shimano’s latest range of 12-speed Di2 road groupsets.
This means the new 12-speed Di2 parts aren’t backwards compatible with the old, 11-speed wires, battery or charger cable.
That aside, the big change is that you now only need two wires – one to the rear derailleur and one to the front derailleur.
Shimano’s claimed weight for the BT-DN300 battery is 52g, but that clearly doesn’t include wires or mounting hardware, because on our scales the whole lot weighed 78g.
- Claimed weight: 52g
- Actual weight: 78g
Shimano GRX Di2 RX825 groupset total weight
| Shimano GRX Di2 RX825 (12-speed) | Claimed weight (grams) | Actual weight (grams) |
|---|---|---|
| ST-RX825 shifters | 415 | 440 |
| RD-RX825 rear derailleur | 310 | 310 |
| FD-RX825-F front derailleur | 142 | 139 |
| FC-RX820-2 crankset (48/31t / 172.5mm) | 721 | 710 |
| CS-R8101-12 cassette (11-34t) / CS-HG710-12 cassette (11-36t) | 345 | 381 |
| BR-RX820 calipers (front and rear) | 282 | 335 |
| RT-CL800 (1600mm pair) / RT-MT900 rotors (140 + 160mm pair) | 228 | 216 |
| CN-M8100 chain (126 links + quick link) | 252 | 283 |
| BT-DN300 battery only / BT-DN300 battery and EW-SD300 wires (850 + 950mm) | 52 | 78 |
| Total | 2747 | 2892 |
All in, Shimano’s GRX Di2 RX825 groupset weighs 2,892g in the spec we have.
That’s up slightly on Shimano’s claimed weights, though it would appear those don’t account for extras such as rotor lockrings, wires, brake hoses and the like.
Perhaps more significantly, that also looks to be up compared to its 11-speed predecessor, GRX Di2 RX815 – which was claimed to weigh around 2,700g in a comparable spec.
| Shimano GRX Di2 RX815 (11-speed) | Claimed weight (grams) |
|---|---|
| ST-RX815 shifters (pair) | 373 |
| RD-RX815 rear derailleur | 287 |
| FD-RX815-F front derailleur | 135 |
| FC-RX810-2 crankset (48/31t / 172.5mm) | 710 |
| CS-HG800-11 cassette (11-34t) | 335 |
| BR-RX810 calipers (front and rear) | 265 |
| SM-RT800 rotors (160m, pair) | 256 |
| CN-HG701-11 chain (114 links) | 257 |
| BT-DN110-A battery | 50 |
| EW-RS910 junction box | 11 |
| Total | 2679 |
As with GRX Di2 RX825, though, we’d expect the actual weight of that groupset to be a little higher once the same extras are accounted for.
The new 12-speed groupset also requires fewer wires overall, and no longer needs a separate junction box either.
Whether those things are enough to close the gap is unclear, but considering Shimano hasn’t made any specific claims about the weight of the new groupset it’s probably safe to bet it has got a little heavier overall.