Skid Patch Calculator for Fixed Gear Bikes
Enter your chainring and cog to see how many skid patches your rear tire gets with one foot or both, plus gear inches, rollout and track chain length.
Fixed-Gear Setup
Reduced: 49/17Skidding with either foot spreads wear over 34 spots.
Skid Patches
17/ 34 ambi
Spacing:10.6°
Gear Inches
76.3"
Ratio:2.88:1
Gain:5.87
Rollout
6.09m
At 90 rpm:32.9 km/h
1/2" Track Chain
98L
Dropout:+2.62 mm
Skid patches on the rear tire (34 spots)
- Dominant foot (17)
- Other foot (+17)
Cadence to speed (49×17)
| Cadence | Speed |
|---|---|
| 60 rpm | 21.9 km/h |
| 75 rpm | 27.4 km/h |
| 90 rpm | 32.9 km/h |
| 100 rpm | 36.5 km/h |
| 110 rpm | 40.2 km/h |
| 120 rpm | 43.8 km/h |
| 130 rpm | 47.5 km/h |
Nearby ratios: single / ambidextrous patches
Select a cell to load that ring and cog. Cells in red have a single skid patch.
| Ring \ Cog | 15T | 16T | 17T | 18T | 19T |
|---|---|---|---|---|---|
| 47T | |||||
| 48T | |||||
| 49T | |||||
| 50T | |||||
| 51T |
How Skid Patches Work
On a fixed gear the rear wheel turns whenever the cranks do, so a skid always stops the wheel at the same crank angles. How many places on the tire that touches depends only on the ratio of ring to cog teeth. Once the tire wears, check the chain with the chain wear calculator, and if you change the ring or cog, the bike chain length calculator shows whether your chain still fits.
The rule
a is the reduced ring count and b the reduced cog count. Fewer common factors mean more patches.
Popular ratios on a 700×25c tire
With a 672 mm wheel, computed by this calculator.
- 49/1717 / 34 patches · 76.3"
- 48/1717 / 17 patches · 74.7"
- 47/1717 / 34 patches · 73.1"
- 51/155 / 10 patches · 90"
- 48/161 / 2 patches · 79.4"
Tire Sizes and Gear Inches
Gear inches is the ratio times the wheel's outer diameter, so the same ring and cog gives a different number on a different tire. To compare with a geared bike, try the sprocket speed calculator, or compare ratios with the gear ratio calculator.
| Tire | Outer diameter (mm) | Gear inches at 49/17 | Rollout (m) |
|---|---|---|---|
| 700×23c | 668 | 75.8 | 6.05 |
| 700×25c | 672 | 76.3 | 6.09 |
| 700×28c | 678 | 76.9 | 6.14 |
| 700×32c | 686 | 77.8 | 6.21 |