Short answer: GRX numbers climb with tier, not with speed count. RX400 is 10-speed, RX600 and RX810 are 11-speed, RX610, RX820 and RX825 are 12-speed. Within a generation, GRX shares cable pull with Shimano road groupsets of the same speed count, so an 11-speed GRX rear derailleur works with 105 R7000 or Ultegra R8000 levers. What does not cross over is the crank: every GRX chainset sits 2.5mm further outboard than its road equivalent, and that offset is the whole point of the group.
Contents
- Reading the RX numbers
- The three generations
- The 2.5mm chainline offset
- What crosses over with road Shimano
- Cassettes and maximum sprocket
- Upgrade paths that work, and three that do not
- What we actually hold
- Frequently asked questions
- Working out what fits your bike
Reading the RX numbers
GRX part codes follow the pattern component prefix, then RX, then a three-digit series. RD-RX810 is a rear derailleur in the RX810 series. FC-RX820-1 is a chainset in the RX820 series, configured for 1x.
The trap is that the series number tells you the tier, not the number of gears. RX810 and RX820 look one apart and are a whole generation apart.
| Series | Speeds | Tier | Shifting |
|---|---|---|---|
| RX400 | 10 | Entry | Mechanical |
| RX600 | 11 | Mid, 105 level | Mechanical |
| RX810 / RX812 | 11 | Top, Ultegra level | Mechanical |
| RX815 | 11 | Top | Di2 |
| RX610 | 12 | Mid | Mechanical |
| RX820 / RX822 | 12 | Top | Mechanical |
| RX825 | 12 | Top | Di2, 2x |
| RX827 | 12 | Top | Di2, 1x |
The prefixes worth knowing: ST is a combined shift and brake lever, BL is a brake lever alone, BR is a caliper, RD and FD are rear and front derailleurs, FC is a chainset, CS a cassette, BB a bottom bracket.
One more: a trailing -1 or -2 on a chainset code means 1x or 2x. FC-RX810-1 is single ring, FC-RX810-2 is double. A trailing SGS on a derailleur means long cage.
The three generations
10-speed, RX400
The entry tier from the original 2019 launch. RD-RX400, FD-RX400, FC-RX600 in its 2x10 form, and the ST-RX400 lever. Largely superseded now, and relevant mainly if you are keeping an older gravel bike running.
11-speed, RX600 and RX810
This is the generation most GRX bikes in India are still built on, and the one where parts remain easy to find. RX600 sits at 105 level, RX810 at Ultegra level, and RX815 is the Di2 version of RX810.
Two rear derailleurs matter here and they are not interchangeable in use. RD-RX810 is the 2x derailleur, short cage, maximum 34T sprocket. RD-RX812 is the 1x derailleur, long cage with a clutch, and takes up to a 42T sprocket. If you are running a single ring, you want the RX812.
12-speed, RX610, RX820 and RX825
The 2023 update. RX820 is the top mechanical tier with a 48/31T chainset, RX610 the mid tier with 46/30T. RX825 is the Di2 version, launched later, with wireless levers and the rear derailleur acting as the system brain.
The 12-speed Di2 rear derailleurs split by configuration. RD-RX825 is the 2x unit and takes a 36T maximum sprocket, with no cage length options. The 1x Di2 option is a separate derailleur, the long-cage RD-RX827-SGS, because the 2x unit cannot reach the wide-range single-ring cassettes.
The 2.5mm chainline offset
This is the single most important compatibility fact about GRX and the reason the group exists as something separate from road Shimano.
Every GRX chainset sits 2.5mm further outboard than the equivalent road chainset. A 12-speed GRX crank runs a 49.7mm chainline where a road crank runs 47.2mm. The front derailleur is offset to match.
Shimano did this for tyre and chainstay clearance. Moving the rings outboard lets a frame use shorter chainstays and still clear a wide gravel tyre, and it keeps the chain off the chainstay in the smallest gears.
The practical consequences:
- A GRX crank needs a GRX front derailleur, and a road crank needs a road front derailleur. Mixing them leaves the cage in the wrong place and no amount of limit screw adjustment fixes it.
- A 1x GRX crank on a road frame is usually fine, because with no front derailleur there is nothing to mismatch. You are simply running a slightly outboard chainline.
- Bottom brackets are shared. GRX uses standard Shimano 24mm Hollowtech II spindles, so the same BB-RS500-PB press-fit or threaded road bottom bracket fits. The offset is built into the crank arms, not the bottom bracket.
What crosses over with road Shimano
Within a speed count, GRX and road Shimano share the same cable pull ratio. That makes far more mixing possible than people assume.
| Combination | Works? | Note |
|---|---|---|
| GRX 11sp rear derailleur with 105 R7000 or Ultegra R8000 levers | Yes | Same pull ratio |
| 105 R7000 rear derailleur with GRX 11sp levers | Yes | But you lose the clutch |
| GRX 11sp chainset with road front derailleur | No | Chainline offset |
| Road 11sp cassette with GRX 11sp derailleur | Yes | Standard HG freehub |
| GRX 11sp parts with 12sp parts | No | Different pull and spacing |
| GRX 12sp Di2 with road 12sp Di2 cassettes | Yes | 11-34T road cassettes are listed as compatible |
| GRX hydraulic calipers with road levers | Yes | Same mineral oil and flat mount |
Brakes are the most freely mixable part of the system. All Shimano road and gravel hydraulics use the same mineral oil, the same SM-BH90 hose and the same flat mount standard, so a GRX caliper on a 105 lever is a perfectly sound build. Pads are shared too: the SwissStop Disc 34 fits across Dura-Ace, Ultegra, 105, Tiagra and GRX.
Cassettes and maximum sprocket
| Rear derailleur | Speeds | Max sprocket | Setup |
|---|---|---|---|
| RD-RX400 | 10 | 34T | 2x |
| RD-RX810 | 11 | 34T | 2x |
| RD-RX812 | 11 | 42T | 1x, clutch |
| RD-RX815 Di2 | 11 | 34T | 2x |
| RD-RX820 | 12 | 36T | 1x or 2x |
| RD-RX825 Di2 | 12 | 36T | 2x only |
| RD-RX827-SGS Di2 | 12 | Wide range | 1x, long cage |
GRX uses standard Shimano HG freehub cassettes throughout, so there is no gravel-specific cassette you must buy. An 11-speed GRX build takes any Shimano 11-speed road or mountain cassette within the derailleur's limit. The 12-speed builds take the HG710 11-36T or the 11-34T road cassettes.
The CS-HG500 10-speed is worth a note: it is sold under the GRX name but it is an ordinary HG500 cassette, and it fits any 10-speed Shimano drivetrain.
For the general rules on sprocket limits and cage capacity, see our reference on cassette and gear ratios.
Upgrade paths that work, and three that do not
Worth doing
- 2x11 to 1x11. Swap to RD-RX812 and a 1x chainset such as FC-RX810-1 or the more affordable FC-RX600-1. You keep the levers and the brakes. The left lever simply stops doing anything.
- RX600 to RX810 within 11-speed. Every part is interchangeable. Upgrade one component at a time as budget allows.
- Adding a clutch. If you run 2x11 and drop chains on rough ground, the RX812 is the only clutched 11-speed GRX derailleur, but it is 1x only. There is no clutched 2x11 GRX option.
- Road to GRX brakes. Straight swap on flat mount.
Not worth doing
- 11-speed to 12-speed piecemeal. Shifters, derailleurs, chain, cassette and chainset all change together. There is no partial path. Budget for the whole group.
- Mechanical to Di2 within a generation. The levers, derailleurs, battery and wiring all change, which is effectively a new groupset with the brakes reused.
- GRX chainset onto a road 2x bike. The offset that helps a gravel frame is a liability on a road frame, and the front derailleur will not line up.
What we actually hold
Compatibility is one thing, availability another. As this is written, everything we have in GRX is 11-speed or 10-speed. The 12-speed parts are listed and orderable but none are on the shelf.
In stock now: RD-RX810 and RD-RX812 rear derailleurs, FD-RX810 front derailleur, FC-RX810-1, FC-RX810-2 and FC-RX600-1 chainsets, the RX810 and RX600 hydraulic brake sets, BB-RS500-PB bottom brackets, SM-BH90 hoses and the CS-HG500 cassette.
If you are building or repairing an 11-speed GRX bike, almost everything you need is here. If you want 12-speed GRX, it is an order rather than a collection, so talk to us about lead time before you strip the bike down.
Complete gravel bikes running GRX are a different matter. The Cannondale Topstone 2 with GRX 2x is in stock, and the rest of the range is in gravel bikes.
Frequently asked questions
Can I run a GRX rear derailleur with SRAM shifters?
No. Shimano and SRAM use different cable pull ratios, so the derailleur will move the wrong distance per click and no adjustment will correct it across the whole cassette. This holds in both directions and across every speed count. The only Shimano and SRAM parts that genuinely interchange are cassettes on an HG freehub body at matching speed counts, and chainrings in some cases. Treat drivetrains as one brand end to end.
Does GRX need a gravel-specific chain?
No. Use the standard Shimano chain for your speed count: an 11-speed GRX drivetrain takes any Shimano 11-speed chain, road or mountain, and a 12-speed GRX takes a 12-speed chain. There is no GRX chain. What does matter is that 11 and 12-speed chains are not interchangeable, because the inner width differs to suit the narrower sprocket spacing, and running the wrong one causes poor shifting and accelerated wear on both.
Why does my GRX chainset foul the frame when a road one did not?
Almost certainly the opposite of what you expect. The GRX crank sits further outboard, so it clears more, not less. If something is fouling, check that the bottom bracket is the right width for the shell and fully seated, and that any spacers specified for your frame standard are fitted. A GRX crank in a 68mm threaded shell without the correct spacers sits too far inboard and the inner ring can catch the chainstay.
Is GRX Di2 wired or wireless?
Both, depending on generation. The 11-speed RX815 Di2 is fully wired, with the levers connected to a junction and battery. The 12-speed RX825 uses wireless shift levers with wires running only between the rear derailleur, the battery and the front derailleur, and the rear derailleur acts as the system's controller and carries the charging port. That means an RX815 bike cannot be upgraded lever-by-lever to RX825, because the communication architecture is different.
What does the clutch on the RX812 actually do, and should I leave it on?
It adds friction to the derailleur cage so the chain is held under tension and cannot slap against the chainstay or bounce off the ring on rough ground. Leave it on for anything unpaved. Switch it off for wheel removal, which is much easier with the cage free, and some riders switch it off on smooth tarmac to save a small amount of drivetrain friction. Forgetting to switch it back on before a rough descent is how chains get dropped.
Working out what fits your bike
If you are unsure which generation your bike is running, the part codes are printed on the components themselves: look on the back of the rear derailleur cage and on the inner face of the crank arm. Bring those two codes and we can tell you exactly what will fit.
Prices are indicative and move with exchange rates and import duty. Standards outlive stock, so parts listed here may be out of stock at any given moment while the compatibility information stays accurate.
Ask TBA Guide with the codes from your derailleur and crank, or bring the bike to the Kondapur workshop.
