Shimano GRX RD-RX820 (2x12) Rear Derailleur
What the checker says74will not fit
Run variant by variant through the road bike builder’s own engine. Every sentence below is the checker’s, unedited. Nothing here says this part fits your bike; it says what it does and does not fit among the parts we hold.
Checked against 1031 verified road bike parts in this catalog. 947 produced no finding of any kind. Each variant produces 54 to 61 distinct errors and 0 distinct warnings.
Will not fit
- Will not fiterror · CassetteDrivetrain mismatch: Rear derailleur = shimano-grx-12, Cassette = sram-axs-road. Shifter, derailleurs and cassette must be one system. On 10 of the 34 verified cassettes in this catalog. Applies to all 2 variants.
- Will not fiterror · Shifter/Brake LeversSpeed mismatch: Shifter 11s, Rear derailleur 12s. The drivetrain must share one speed count. On 8 of the 25 verified shifter/brake levers in this catalog. Applies to all 2 variants.
- Will not fiterror · CassetteDrivetrain mismatch: Rear derailleur = shimano-grx-12, Cassette = shimano-road-12. Shifter, derailleurs and cassette must be one system. On 7 of the 34 verified cassettes in this catalog. Applies to all 2 variants.
- Will not fiterror · Front DerailleurDrivetrain mismatch: Front derailleur = shimano-road-12, Rear derailleur = shimano-grx-12. Shifter, derailleurs and cassette must be one system. On 6 of the 22 verified front derailleurs in this catalog. Applies to all 2 variants.
- Will not fiterror · Shifter/Brake LeversDrivetrain mismatch: Shifter = shimano-road-11, Rear derailleur = shimano-grx-12. Shifter, derailleurs and cassette must be one system. On 6 of the 25 verified shifter/brake levers in this catalog. Applies to all 2 variants.
- Will not fiterror · CassetteSpeed mismatch: Rear derailleur 12s, Cassette 11s. The drivetrain must share one speed count. On 5 of the 34 verified cassettes in this catalog. Applies to all 2 variants.
- Will not fiterror · CassetteDrivetrain mismatch: Rear derailleur = shimano-grx-12, Cassette = shimano-road-11. Shifter, derailleurs and cassette must be one system. On 5 of the 34 verified cassettes in this catalog. Applies to all 2 variants.
- Will not fiterror · Front DerailleurDrivetrain mismatch: Front derailleur = shimano-road-11, Rear derailleur = shimano-grx-12. Shifter, derailleurs and cassette must be one system. On 5 of the 22 verified front derailleurs in this catalog. Applies to all 2 variants.
Rg actuation, Shifter/Brake Levers. 29 more findings from the same check, on up to 1 of the 25 verified shifter/brake levers each.
Rg chain std, Chain. 8 more findings from the same check, on up to 1 of the 25 verified chains each.
Rg drivetrain system, Shifter/Brake Levers. 7 more findings from the same check, on up to 3 of the 25 verified shifter/brake levers each.
Rg drivetrain system, Cassette. 6 more findings from the same check, on up to 3 of the 34 verified cassettes each.
Rg drivetrain system, Front Derailleur. 5 more findings from the same check, on up to 4 of the 22 verified front derailleurs each.
Rg drivetrain speeds, Cassette. 4 more findings from the same check, on up to 3 of the 34 verified cassettes each.
Rg rd capacity, Cassette. 4 more findings from the same check, on up to 3 of the 34 verified cassettes each.
Rg drivetrain speeds, Shifter/Brake Levers. 3 more findings from the same check, on up to 1 of the 25 verified shifter/brake levers each.
Open a variant in the builder to see the ones that apply to your own parts.
$130.00 to $500.00 MSRP·280 to 449 g
What the maker states
- System
- Drivetrain system shimano-grx-12
- Speeds
- 12-speed (rear index count the maker rates it for)
- Actuation
- Di2-wired (on 1 of 2 variants); Mechanical (on 1 of 2 variants)
- Maximum cog
- Largest cog 36 teeth (on 1 of 2 variants); Largest cog 51 teeth (on 1 of 2 variants)
- Mount
- Std-hanger
- Cage
- long cage (on 1 of 2 variants); medium cage (on 1 of 2 variants)
A value shown as a set or a range differs between this model’s variants and is never one variant’s spec.
2 verified variants
| Variant | Actuation | Maximum cog | Cage | Price (MSRP) | Weight | Source | Last checked | Build |
|---|---|---|---|---|---|---|---|---|
| GRX RD-RX820 (2x12) | mechanical | Largest cog 36 teeth | medium cage | $130.00 | 280 g | maker’s page | 2026-07-18 | Build with this |
| GRX Di2 RD-RX827-SGS (1x12) | di2-wired | Largest cog 51 teeth | long cage | $500.00 | 449 g | maker’s page | 2026-08-15 | Build with this |
Source
Source: each variant links the maker’s own page in the table above. Last checked 2026-07-18 to 2026-08-15.
Checked against
The checker ran this model against every verified part below that it has a slot for, the same way it checks a build in the builder. What follows is the verdict it actually produced for that specific pairing — not a recommendation, and not a guarantee any of these parts fits your own bike.
- 3T Aeroflux Integrale (Handlebar) No conflicts found
- 3T Apto Stealth Stem (Stem) No conflicts found
- 3T Superergo LTD (standard, non-INTEGRALE) (Handlebar) No conflicts found
- All-City Zig Zag Frameset (Frame) No conflicts found
- Argon 18 SUM D-Shape Seatpost (Seatpost) No conflicts found
- Argon 18 Sum Frameset (Frame) No conflicts found
6 of 696 counterparts with a page of their own that the checker actually probed this model against, in alphabetical order by brand and model — never by price, popularity or the verdict itself.