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
Results
- Skid patches (one foot)
- 17
- Ambidextrous patches
- 34
How the number is made
Patches = cog ÷ gcd(chainring, cog). If that count is odd, ambidextrous skidding (both feet forward) doubles it. An even count stays the same because both feet hit the same patches.
Prime cogs against a non-multiple chainring maximise patches. This does not make a bad gear ratio a good one.
Related calculators
- Bicycle Gear Ratio Calculator
Patches save the tyre; the ratio still decides whether you can climb.
- Optimal Chain Length Calculator
A track chain is sized on one ring and one cog, with no derailleur slack.
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 does not.
Is 48×17 enough patches?
gcd(48, 17) is 1, so 17 one-foot patches and 34 ambidextrous. That is a friendly combination.
Does a prime cog always give one patch per tooth?
No. A prime cog shares a divisor only when the chainring is a multiple of that prime. 51 by 17 still has one patch, not seventeen.
Related gear
- Fixed cog
A 17 T cog against 48 T is a classic high patch count because 17 is prime.
$20–$60