Speedometer Difference

Estimate actual speed after a tire diameter change.

Your numbers

Enter your numbers to see the result.

How Speedometer Difference works

Estimated actual speed = displayed speed × new tire diameter ÷ original diameter. Subtract displayed speed to find the difference.

A worked example

These sample values illustrate the calculation. Use your own numbers in the calculator for your result.

Example inputs
Original tire diameter (in)
25
New tire diameter (in)
26
Indicated speed (mph)
60
Approximate actual speed
62.4 mph
Speed difference
2.4 mph

Assumptions and limits

Assumes the speedometer was calibrated to the original tire diameter. Confirm tire compatibility separately.

Check lender terms and manufacturer guidance. These estimates do not replace a mechanical inspection.