Tire Size Calculator
Compare two tire sizes like 225/45R17 side by side: diameter, sidewall, circumference, revolutions per mile and the speedometer error between them.
Side-by-side comparison
| Specification | Tire 1 | Tire 2 | Difference |
|---|---|---|---|
| Overall diameter | – | – | – |
| Section width | – | – | – |
| Sidewall height | – | – | – |
| Circumference | – | – | – |
| Revolutions per mile | – | – | – |
| Revolutions per km | – | – | – |
Про Tire Size Calculator
The Tire Size Calculator decodes metric tire sizes like 225/45R17 and compares two of them side by side. For each size it works out the sidewall height, overall diameter, circumference and revolutions per mile and per kilometre, then reports the percentage difference in diameter and the speedometer error that difference causes.
Metric sizing is a mix of units: the first number is the section width in millimetres, the second is the aspect ratio (sidewall height as a percentage of the width), and the last is the rim diameter in inches. Overall diameter is the rim plus two sidewalls, which is why a lower profile on a bigger wheel can keep the same rolling diameter.
Use it when plus-sizing wheels, checking whether a staggered set will fit, or working out why your speedometer reads high after a tire change. As a rule of thumb, keep the diameter change within ±3% of the original. Free, instant and browser-based.
Як використовувати Tire Size Calculator
- Enter the width, aspect ratio and rim diameter of your current tire (for 225/45R17: 225, 45, 17).
- Enter the same three numbers for the tire you are considering.
- Read the diameter difference as a percentage — stay within about ±3%.
- Check the speedometer comparison to see your true speed with the new size.
- Review the full table for sidewall, circumference and revolutions per mile.