Shimano Ultegra CS-R8101-12 Cassette
What the checker says160will 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 1026 verified road bike parts in this catalog. 898 produced no finding of any kind. Each variant produces 99 to 102 distinct errors and 0 distinct warnings.
Will not fit
- Will not fiterror · Shifter/Brake LeversSpeed mismatch: Shifter 11s, Cassette 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 · Rear DerailleurSpeed mismatch: Rear derailleur 11s, Cassette 12s. The drivetrain must share one speed count. On 6 of the 29 verified rear derailleurs in this catalog. Applies to all 2 variants.
- Will not fiterror · Shifter/Brake LeversDrivetrain mismatch: Shifter = shimano-road-11, Cassette = shimano-road-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 · Front DerailleurDrivetrain mismatch: Front derailleur = shimano-road-11, Cassette = shimano-road-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.
- Will not fiterror · Rear DerailleurDrivetrain mismatch: Rear derailleur = shimano-grx-12, Cassette = shimano-road-12. Shifter, derailleurs and cassette must be one system. On 5 of the 29 verified rear derailleurs in this catalog. Applies to all 2 variants.
Rg freehub, Rear Wheel. 114 more findings from the same check, on up to 1 of the 112 verified rear wheels 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, Rear Derailleur. 8 more findings from the same check, on up to 4 of the 29 verified rear derailleurs each.
Rg drivetrain system, Shifter/Brake Levers. 7 more findings from the same check, on up to 4 of the 25 verified shifter/brake levers each.
Rg drivetrain system, Front Derailleur. 6 more findings from the same check, on up to 4 of the 22 verified front derailleurs each.
Rg rd capacity, Rear Derailleur. 5 more findings from the same check, on up to 1 of the 29 verified rear derailleurs each.
Rg drivetrain speeds, Rear Derailleur. 4 more findings from the same check, on up to 3 of the 29 verified rear derailleurs 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 MSRP·291 to 345 g
What the maker states
- Speeds
- 12-speed (rear index count the maker rates it for)
- System
- Drivetrain system shimano-road-12
- Freehub
- / driver hg-road
- Minimum cog
- Smallest cog 11 teeth
- Maximum cog
- Largest cog 30 teeth (on 1 of 2 variants); Largest cog 34 teeth (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 | Maximum cog | Price (MSRP) | Weight | Source | Last checked | Build |
|---|---|---|---|---|---|---|
| Ultegra CS-R8101-12 11-30 | Largest cog 30 teeth | $130.00 | 291 g | maker’s page | 2026-07-20 | Build with this |
| Ultegra CS-R8101-12 11-34 | Largest cog 34 teeth | $130.00 | 345 g | maker’s page | 2026-08-01 | Build with this |
Source
Source: each variant links the maker’s own page in the table above. Last checked 2026-07-20 to 2026-08-01.
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 697 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.