Formula
Distance per revolution is the circumference. Speed multiplies that by revolutions per minute:
mph = rpm × π × diameter inches × 60 / 63,360
The diameter is the same sidewall formula as the tire size page. This page's result is miles per hour, not the diameter.
Assumptions
- The revolutions are at the wheel.
- The tire is at its nominal diameter.
- There is no slip.
Worked example
A 225/50R17 tire at 772 wheel revolutions per minute is traveling at 59.4 mph.
Input definitions
- Wheel revolutions
- How fast the tire rotates. An engine speed has to be divided by the gear ratio first.
- 63,360
- The number of inches in a mile.
Limitations
This uses the nominal size, not a mounted measurement. Confirm the load index, speed rating, and clearance before the tire is installed.
Questions
Can I enter engine rpm?
Only if the gear ratio is 1. Otherwise divide engine speed by the overall ratio before using this page.
Why is the diameter not the result?
The tire size page already reports diameter and revolutions per mile. This page converts a rotational speed into road speed.