CYCLE CALCULATORS

CalculatorsFixie Skid Patch Calculator

Fixie Skid Patch Calculator

A fixed gear skids on the same tyre spots unless the chainring and cog spread those spots out. More patches means the tyre lasts longer.

Inputs

Units

Results

Skid patches (one foot)
17
Ambidextrous patches
17

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

Reduce chainring ÷ cog to lowest terms p/q by dividing both by their gcd. One-foot patches = q. If p is odd, skidding with either foot forward doubles that to 2q; if p is even, both feet land on the same q patches. Example: 44×16 = 11/4 → 4 patches, 8 with either foot.

Prime cogs against a non-multiple chainring maximise one-foot patches, and an odd chainring doubles them for riders who skid with either foot. This does not make a bad gear ratio a good one.

Related calculators

Questions

Why do prime cogs help?

A prime cog shares a divisor only when the chainring is a multiple of that prime. Otherwise gcd is 1 and you get one patch per cog tooth. A 51 T ring with a 17 T cog reduces to 3/1 and leaves a single patch.

Is 48×17 enough patches?

gcd(48, 17) is 1, so one foot gets 17 patches. 48 is even, so the other foot lands on the same 17; a 47 or 49 T ring would give 34 to a rider who skids with either foot. 17 is still a friendly count.

When does skidding with either foot double the patches?

When the chainring is still odd after dividing out the common factor. 44×16 reduces to 11/4: 4 patches with one foot, 8 with either. 42×15 reduces to 14/5: 5 patches either way.

Example products

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