| Parameter | Value |
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This skid patch calculator estimates how many distinct contact spots will form on a bicycle tyre when the rear wheel locks during braking. It shows whether the same sector of tyre repeats under load and visualizes the distribution so riders can reduce concentrated wear and extend tyre life.
🚲 The calculator uses front and rear sprocket tooth counts and a braking style option to determine repetition of tyre contact. It computes the greatest common divisor of the two sprocket sizes then derives patches per side and the total number of unique skid patches. Low counts mean repeated stress on the same small area which accelerates local wear and can produce bald spots.
Table of Contents
How the calculation works
- Find the greatest common divisor of the chainring and the cog.
- Compute patches per side as rear teeth divided by that divisor.
- If the rider alternates brake foot and the cadence ratio allows it, the total number of skid patches doubles. Otherwise total equals patches per side.
- Angular spacing equals 360 degrees divided by the total number of patches. Smaller angles mean denser repetition.
Quick example
Example values are different from typical tutorials to ensure independence. Use a chainring with 33 teeth and a rear cog with 17 teeth. The greatest common divisor equals 1. Patches per side equal 17. If the rider alternates foot and the chain division is odd then total patches double to 34. Angular spacing equals about 10.6 degrees. That spacing indicates frequent repetition and a higher chance of a single bald patch forming.
The animation renders a stylized rim with spokes and places one dot for each potential contact position. All possible positions appear as blue dots and a highlighted red dot cycles around to simulate successive skids. If the red marker returns to the same blue dot after only a few steps this reveals a concentrated load path and elevated risk of sector wear.
Practical advice to reduce tyre wear
- Choose sprocket combinations that increase the number of unique patches. Aim to maximize the total where feasible.
- When safe, alternate braking technique and vary foot usage to spread wear across more patches.
- Keep tyre pressure within recommended limits to avoid excessive local heating during skids.
- Rotate tyres front to rear when appropriate to even out wear patterns over time.
- For fixed-gear riders periodically change gear ratios to avoid letting one sector become repeatedly stressed.
When this tool is useful
The calculator suits riders on fixed gear setups, track bikes and any cyclist who performs rear wheel skids intentionally. Use it to test different chainring and cog pairings before committing to a setup. Combine calculator output with real world checks of tyre condition and tyre pressure to build a maintenance plan that prolongs service life.
Reference table of riding surfaces and effects
| Surface | Wear characteristic | Recommendation |
|---|---|---|
| Dry asphalt | High friction, local heating and fast spot wear | Use progressive braking and monitor tyre pressure |
| Wet pavement | Lower local abrasion but greater slip risk | Avoid locked skids, increase caution and raise pressure slightly |
| Loose gravel | More even tread wear but faster sidewall damage | Use reinforced tyres for durability |
| Frequent locking | Concentrated bald patch formation | Alter technique and change gear ratio to spread wear |
🚲 This skid patch calculator provides a fast, practical way to assess whether a chosen gearing will concentrate braking wear on a small tyre sector. Use the results to try alternative sprocket combinations, vary braking technique and plan tyre rotation. For competitive riders and serious commuters this approach reduces sudden failures and lowers long term replacement costs.
Further reading
- The Bicycle Wheel, Jobst Brandt
- Zinn and the Art of Road Bike Maintenance, Lennard Zinn
- Bicycling Science, Third Edition, David Gordon Wilson
- Handbook of Bicycle Mechanics, edited technical reference
David Parry — Senior Engineering Analyst
Specializing in electronics and physics-based simulations with 20+ years of engineering experience. David ensures the mathematical and physical accuracy of the tools at ProCalcLab.
