CYCLE CALCULATORS

CalculatorsDerailleur Capacity Calculator

Derailleur Capacity Calculator

Capacity is how much slack the cage must swallow between big-big and small-small. A 1× setup uses the same tooth count for both chainring fields.

Inputs

Units
For 1×, enter the same tooth count twice.

Results

Total capacity
39 T
Cage code
2

The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.

How the number is made

Capacity = (big ring − small ring) + (big cog − small cog). Cage code 1 is a short cage up to 33 T, 2 is medium up to 39 T, 3 is long up to 47 T, 4 exceeds those bands.

Published cage capacities differ by brand. These bands follow Shimano: short cages take 33–35 T, Ultegra R8000 GS and XT M8000 GS 39 T, and XT M8000 SGS 47 T. Capacity is one limit; the spec sheet also sets the largest cog and the maximum front difference.

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Questions

What if I only have one chainring?

Enter it as both the large and the small ring. Capacity is then just the cassette spread.

Is a longer cage always safer?

It wraps more chain. It can also hang closer to rocks. Use the shortest cage that clears your capacity.

What cage does 52/36 with 11-34 need?

Capacity is (52 minus 36) plus (34 minus 11), which is 39 teeth. That is cage code 2: Shimano’s medium GS road cage is rated for exactly 39 T and a 34 T cog.

Example products

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