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Shimano GRX 12-speed compatibility: cassettes, freehubs, wheels and chains
Which cassette, freehub body, wheel and chain each GRX 12-speed rear derailleur takes, from Shimano's spec tables and lineups, and the three places Shimano's own pages disagree.
At a glance
Who it's for: gravel riders on Shimano GRX 12-speed, or about to buy into it, who want to know which cassette, freehub body, wheel and chain fit their rear derailleur before the parts box arrives.
The short answer
GRX 12-speed splits by rear derailleur, not by groupset name. The derailleur decides the cassette, and the cassette decides the freehub.
- 2x, or 1x with a road cassette (RD-RX820, and RD-RX825 for Di2 2x): Shimano 12-speed road cassettes, 11-34T or 11-36T, on an HG road freehub.
- 1x with 10-45T or 10-51T (RD-RX822-GS, RD-RX822-SGS, and the Di2 RD-RX827-SGS and RD-RX717-SGS): Shimano 12-speed MTB cassettes on a MICRO SPLINE freehub.
- Chain: every GRX 12-speed lineup Shimano publishes uses an HG 12-speed chain (CN-M8100, CN-M7100 or CN-M6100) and the SM-CN910-12 QUICK-LINK.
- Not listed: 9-45T cassettes and LINKGLIDE (CUES) cassettes.
Shimano's own pages disagree in three places. The one that matters most is whether 12-speed road cassettes fit the older 11-speed road freehub (HG spline L), because it decides whether your current wheels can stay (see Sources and notes).
Which derailleur takes which cassette
From Shimano's GRX lineup pages and each derailleur's spec table. "Largest cog" is the spec table's low sprocket minimum and maximum.
| Rear derailleur | Shifting | Cassettes in Shimano's lineups | Freehub | Largest cog | Total capacity | Hangers ticked |
|---|---|---|---|---|---|---|
| RD-RX820 | Mechanical, 2x or 1x | CS-R8101-12 11-34T, CS-R7101-12 11-34T, CS-HG710-12 11-36T | HG road | 34T to 36T | 42T | Road direct attachment, road direct mount, UDH |
| RD-RX825 | Di2 2x | CS-R8101-12 11-34T, CS-HG710-12 11-36T | HG road | 34T to 36T | 40T | Road direct attachment, road direct mount, UDH |
| RD-RX822-GS | Mechanical 1x | CS-M8100-12 or CS-M7100-12, 10-45T | MICRO SPLINE | 45T only | 35T | Road direct attachment, UDH |
| RD-RX822-SGS | Mechanical 1x | 10-51T: CS-M8100-12, CS-M8200-12, CS-M7200-12, CS-M7100-12, CS-M6200-12 | MICRO SPLINE | 51T only | 41T | Road direct attachment, UDH |
| RD-RX827-SGS | Di2 1x, wireless | CS-M8200-12 or CS-M7200-12, 10-51T | MICRO SPLINE | 51T only | 41T | Shimano MTB direct attachment, UDH |
| RD-RX717-SGS | Di2 1x, wireless | CS-M7200-12, CS-M6200-12 or CS-M6100-12, 10-51T | MICRO SPLINE | 51T only | 41T | Shimano MTB direct attachment, UDH |
- Mechanical shifters. ST-RX820-R appears in both the 2x and 1x RX820 lineups, and ST-RX610-R in both RX610 lineups. The 1x lineups for both list RD-RX820, RD-RX822-GS and RD-RX822-SGS as options.
- Di2 power. RD-RX825's spec table ticks "Wired", and the 2x Di2 lineup lists the BT-DN300 internal battery. RD-RX827-SGS and RD-RX717-SGS tick "Built-in battery" (BT-DN320 in the 1x Di2 and RX717 lineups) and use SHADOW ES instead of SHADOW RD+.
Capacity, done the slow way. Total capacity is (big ring minus small ring) plus (largest cog minus smallest cog). FC-RX820-2 is 48-31T, so 17T up front. With 11-36T that's 17 + 25 = 42T, exactly RD-RX820's 42T. RD-RX825's spec table says 40T, which covers 48-31 with 11-34T (17 + 23 = 40) but not with 11-36T. Yet the same spec table gives a largest cog of up to 36T, and Shimano's Di2 2x lineup lists CS-HG710-12 11-36T next to FC-RX820-2 and RD-RX825. We flag it below rather than pick one. Our derailleur capacity checker does the sum for other combinations.
Freehubs: MICRO SPLINE, HG L2 and HG L
Shimano's freehub and cassette spline chart (C-731) lists four bodies that matter here:
- MICRO SPLINE: 23 effective spline teeth, 26 mm body. Ticked for MTB 12-speed only.
- HG spline L2 "(ROAD 12-speed dedicated)": 18 teeth, 37.65 mm. Ticked for ROAD 12-speed only, so no 11-speed cassettes.
- HG spline L "(ROAD 12/11-speed)": 9 teeth, 36.75 mm. Ticked for ROAD 12-speed with no footnote, and for ROAD 11-speed and MTB 11-speed with spacer footnotes.
- HG spline M "(10/9/8/7-speed, MTB 11-speed)": 34.9 mm. Not ticked for ROAD 12-speed.
The same table is in Shimano's Products Compatibility Information PDF (Ver 2.7, Oct. 7, 2026).
The 1x setups are simple: every 10-45T and 10-51T cassette in the table above ticks MICRO SPLINE and nothing else on its spec table.
Road cassette on an HG L wheel? Shimano's own pages disagree on this one, so our advice is to confirm with Shimano or your shop. The details are under Sources and notes at the bottom.
Indoor riders: a GRX 1x MICRO SPLINE cassette needs a trainer with a MICRO SPLINE body. Our trainer drivetrain compatibility guide covers what each trainer brand offers.
Shimano's GRX-era wheels
All three are 700c with 142 x 12 mm E-THRU rears, 25 mm internal rims and a recommended tire size of 32-622 to 50-622, per their productinfo spec tables.
- WH-RX880 (carbon, 32 mm rim): MICRO SPLINE or HG spline L2, not HG spline L. DIRECT ENGAGEMENT hub. Ride Shimano sells the rear in both bodies. The L2 version won't take an 11-speed cassette, per C-731.
- WH-RX870 (carbon, 32 mm rim): HG spline L only, rear speeds "12/11", pawl ratchet hub.
- WH-RX180 (aluminum, 21 mm rim): MICRO SPLINE or HG spline L, rear speeds "12/11".
Shimano's RX870 pages disagree on MICRO SPLINE support (see Sources and notes). For a 1x MICRO SPLINE wheel from this family, RX880 and RX180 are the ones Shimano's spec tables tick.
Chains and cranks
- Chain: the RX820 lineups (mechanical and Di2) list CN-M8100, RX610 lists CN-M7100 and RX717 lists CN-M6100. All three spec tables say "HG 12-speed". Joining link: SM-CN910-12, "QUICK-LINK for HG 12-speed chain". Length depends on the setup; our chain length calculator has GRX RX820, RX822 and RX825 presets.
- Cranks: FC-RX820-2 is 48-31T with a 47 mm chain line. FC-RX820-1 comes in 40T, 42T, 44T and 46T with a 49.7 mm chain line. The RX610 lineups list FC-RX610-2 at 46-30T and FC-RX610-1 at 40T/38T. To compare ranges before buying, the gear calculator does that with your tire width.
What doesn't mix
- 9-45T cassettes. CS-M8200-12 comes in 9-45T as well as 10-51T, and its spec table ticks MICRO SPLINE. Ride Shimano lists 9-45T for the RX880 MICRO SPLINE body. But every GRX 12-speed derailleur's spec table gives a smallest top sprocket of 10T (1x) or 11T (2x). The wheel will take it; your GRX derailleur isn't listed for it.
- 10-45T on an SGS, or 10-51T on a GS. RD-RX822-GS lists a 45T largest cog as both minimum and maximum. RD-RX822-SGS does the same at 51T. Pick the derailleur that matches the cassette.
- CUES and LINKGLIDE. Shimano's LINKGLIDE chart (C-649) says: "LINKGLIDE cassette are not compatible with MICRO SPLINE FREEHUB."
- 11-speed parts. The spec tables for every GRX 12-speed rear derailleur and for ST-RX820-R say "Rear speeds 12".
Common upgrade questions
- 2x now, 1x with 10-51T later. New derailleur (RD-RX822-SGS, or RD-RX827-SGS for Di2), a 1x crank, a 10-51T MICRO SPLINE cassette, a MICRO SPLINE freehub or wheel, and a new chain length. On mechanical, Shimano lists the same ST-RX820-R right lever in both lineups. To see how the low and top gears change, put both setups into our gear calculator with its A vs B compare (enter 10-51T as custom cogs).
- 1x without a new wheel. Shimano's RX820 1x lineup lists RD-RX820 with CS-R8101-12 11-34T or CS-HG710-12 11-36T and FC-RX820-1. Narrower range than 10-51T, but it keeps an HG wheel (see the HG spline L conflict above). The gear calculator has 11-34T and 10-45T presets if you want to compare.
- Di2 1x on a frame without UDH. RD-RX827-SGS and RD-RX717-SGS tick "SHIMANO MTB type" direct attachment and UDH, and show "-" for the road-type hanger rows. Ask your frame maker. Our UDH and Full Mount gravel frames guide lists frames with UDH.
Related on Pedal Brief
- Smart trainer drivetrain compatibility: 12 and 13-speed: freehub bodies by trainer brand
- UDH and Full Mount gravel frames: which frames take a UDH derailleur
- Compatibility quick reference: chain length, derailleur capacity and freehub answers on one page
- Tools: chain length, derailleur capacity, gear calculator
Sources and notes
Notes and caveats
RX870 conflict. The Ride Shimano RX870 page lists "HG L2 freehub body compatible with 12-speed 11-30T, 11-34T, and 11-36T cassettes" and "MICRO SPLINE freehub body compatible with 12-speed 9-45T, 10-45T, and 10-51T cassettes" as features. The same page also says "Compatible with road 11- and 12-speed drivetrains for varied setups (not compatible with 12-speed Micro Spline cassettes)", and the only freehub option offered is "HG". The productinfo spec table agrees with the second set.
Where Shimano's pages disagree
Where it gets awkward. The spec tables for CS-R8101-12, CS-R7101-12 and CS-HG710-12 tick "HG spline L2 (ROAD 12-speed dedicated)" and show "-" for "HG spline L (ROAD 12/11-speed)". C-731, on the web and in the PDF, ticks ROAD 12-speed for HG spline L. And Shimano's mechanical 2x and 1x lineups list those cassettes next to a "WH-RX180-TL-R12-700C ... HG spline L spec." rear wheel. Two Shimano answers. Our advice, not Shimano's: if you plan to run a GRX 12-speed road cassette on an 11-speed-era HG spline L freehub, confirm with Shimano or your shop before you order.
- 12-speed road cassettes on HG spline L. C-731 (web and PDF Ver 2.7): ROAD 12-speed ticked for HG spline L. CS-R8101-12, CS-R7101-12 and CS-HG710-12 spec tables: "-" for HG spline L, ticked for L2. The mechanical GRX lineups pair them with a WH-RX180 rear labelled "HG spline L spec."
- RD-RX825 with 11-36T. RD-RX825 spec table: total capacity 40T, low sprocket 34T to 36T. Di2 2x lineup: FC-RX820-2 48-31T with CS-HG710-12 11-36T, which by the formula above needs 42T.
- WH-RX870 freehub. Productinfo spec table: HG spline L only. Ride Shimano: HG L2 and MICRO SPLINE in the feature list, but "not compatible with 12-speed Micro Spline cassettes" and an HG-only freehub option on the same page.
Our advice, not Shimano's: for conflicts 1 and 2, confirm with Shimano or your shop before you order.
What we could not confirm
- Which HG spline L answer is current (conflict 1), and RD-RX825 with 48-31T and 11-36T (conflict 2). We found no Shimano note explaining either.
- Freehub body part numbers for switching WH-RX880 or WH-RX180 between bodies, and swapping an RD-RX822 cage between GS and SGS. Not on a Shimano page we could load on 19 October. Shimano's main site, bike.shimano.com, showed a maintenance page that day, and its dealer's manuals didn't load for us.
- Road-type hangers with RD-RX827-SGS and RD-RX717-SGS. The spec tables show "-", which isn't the same as a stated "no".
Sources
- Shimano compatibility charts: FREEHUB and cassette spline compatibility C-731, LINKGLIDE cassette and FREEHUB compatibility C-649, Products Compatibility Information PDF, Ver 2.7, Oct. 7, 2026
- Shimano GRX lineups: RX820 2x12, RX820 1x12, RX820 2x12 Di2, RX820 1x12 Di2, RX610 2x12, RX610 1x12, RX717 1x12 Di2
- Shimano spec tables, derailleurs and levers: RD-RX820, RD-RX825, RD-RX822-GS, RD-RX822-SGS, RD-RX827-SGS, RD-RX717-SGS, ST-RX820-R
- Shimano spec tables, cassettes: CS-R8101-12, CS-R7101-12, CS-HG710-12, CS-M8100-12, CS-M8200-12, CS-M7200-12, CS-M7100-12, CS-M6200-12, CS-M6100-12
- Shimano spec tables, chains and cranks: CN-M8100, CN-M7100, CN-M6100, SM-CN910-12, FC-RX820-1, FC-RX820-2
- Shimano spec tables, wheels: WH-RX880-TL-R12-700C, WH-RX870-TL-R12-700C, WH-RX180-TL-R12-700C
- Ride Shimano (US store): WH-RX880, WH-RX870
All sources checked 19 October 2026 (Europe/Copenhagen).
Disclosure: Pedal Brief may earn a commission if you buy through links on this page, at no extra cost to you. This version has no affiliate links. We have not tested these parts. Every compatibility fact below comes from Shimano's product information site, its Products Compatibility Information PDF (Ver 2.7, Oct. 7, 2026) or Shimano's US store, Ride Shimano, and was checked on 19 October 2026. This guide lists no prices. Full disclosures.