Shimano GRX RD-RX815 Rear Derailleur
What the checker says69will not fit
Run variant by variant through the gravel 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 861 verified gravel bike parts in this catalog. 816 produced no finding of any kind. Each variant produces 48 to 51 distinct errors and 0 distinct warnings.
Will not fit
- Will not fiterror · CassetteSpeed mismatch: Rear derailleur 11s, Cassette 12s. The drivetrain must share one speed count. On 8 of the 18 verified cassettes in this catalog. Applies to all 2 variants.
- Will not fiterror · Shifter/Brake LeversSpeed mismatch: Shifter 12s, Rear derailleur 11s. The drivetrain must share one speed count. On 5 of the 17 verified shifter/brake levers in this catalog. Applies to all 2 variants.
- Will not fiterror · CassetteCassette too big: 44T cassette exceeds the Shimano GRX RD-RX815 max of 34T. On 5 of the 18 verified cassettes in this catalog. Applies to 1 of 2 variants.
- Will not fiterror · CassetteCassette too big: 44T cassette exceeds the Shimano GRX RD-RX817 max of 42T. On 5 of the 18 verified cassettes in this catalog. Applies to 1 of 2 variants.
- Will not fiterror · CassetteSpeed mismatch: Rear derailleur 11s, Cassette 13s. The drivetrain must share one speed count. On 4 of the 18 verified cassettes in this catalog. Applies to all 2 variants.
- Will not fiterror · CassetteDrivetrain mismatch: Rear derailleur = shimano-grx-11, Cassette = shimano-grx-12. Shifter, derailleurs and cassette must be one system. On 4 of the 18 verified cassettes in this catalog. Applies to all 2 variants.
- Will not fiterror · Front DerailleurDrivetrain mismatch: Front derailleur = sram-axs-road, Rear derailleur = shimano-grx-11. Shifter, derailleurs and cassette must be one system. On 4 of the 11 verified front derailleurs in this catalog. Applies to all 2 variants.
- Will not fiterror · Shifter/Brake LeversDrivetrain mismatch: Shifter = shimano-grx-12, Rear derailleur = shimano-grx-11. Shifter, derailleurs and cassette must be one system. On 4 of the 17 verified shifter/brake levers in this catalog. Applies to all 2 variants.
Rg actuation, Shifter/Brake Levers. 28 more findings from the same check, on up to 1 of the 17 verified shifter/brake levers each.
Rg rd capacity, Cassette. 9 more findings from the same check, on up to 2 of the 18 verified cassettes each.
Rg chain std, Chain. 6 more findings from the same check, on up to 1 of the 17 verified chains each.
Rg drivetrain system, Cassette. 6 more findings from the same check, on up to 3 of the 18 verified cassettes each.
Rg drivetrain system, Shifter/Brake Levers. 6 more findings from the same check, on up to 2 of the 17 verified shifter/brake levers each.
Rg drivetrain system, Front Derailleur. 3 more findings from the same check, on up to 2 of the 11 verified front derailleurs each.
Rg drivetrain speeds, Shifter/Brake Levers. 2 more findings from the same check, on up to 3 of the 17 verified shifter/brake levers each.
Rg drivetrain speeds, Cassette. 1 more finding from the same check, on up to 3 of the 18 verified cassettes each.
Open a variant in the builder to see the ones that apply to your own parts.
$300.00 to $350.00 MSRP·287 to 318 g
What the maker states
- System
- Drivetrain system shimano-grx-11
- Speeds
- 11-speed (rear index count the maker rates it for)
- Actuation
- Di2-wired
- Maximum cog
- Largest cog 34 teeth (on 1 of 2 variants); Largest cog 42 teeth (on 1 of 2 variants)
- Mount
- Std-hanger
- Cage
- gs cage
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 | Maximum cog | Price (MSRP) | Weight | Source | Last checked | Build |
|---|---|---|---|---|---|---|
| GRX RD-RX815 | Largest cog 34 teeth | $350.00 | 287 g | maker’s page | 2026-08-15 | Build with this |
| GRX RD-RX817 | Largest cog 42 teeth | $300.00 | 318 g | maker’s page | 2026-08-15 | Build with this |
The rest of what the maker states2 not published
2 further fields the checker looks for are not published by Shimano, so we leave them blank rather than estimate them, and those 2 checks stay silent on this rear derailleur. They are maximum cog top and total capacity. Each is recorded as “not stated by the maker (not checked)”.
Source: each variant links the maker’s own page in the table above. Last checked 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 Exploro Race (Frame) No conflicts found
- 3T Fango LTD (Fork) No conflicts found
- 8bar Gravel Carbon Disc Fork v2 (Fork) No conflicts found
- 9point8 Fall Line R (Dropper Post) No conflicts found
- Acros ZS44/28.6 | EC44/40 Headset (Headset) No conflicts found
- All-City Cosmic Stallion LTD (Frame) No conflicts found
6 of 506 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.