Tire Size Diameter Calculator

1) What’s the difference between metric and flotation sizing?

Metric uses width in millimeters and aspect ratio percentage with an inch rim. Flotation lists overall diameter and section width directly in inches.

2) How precise are the results?

Values are geometric estimates from nominal sizes. Actual tires vary by model, load rating, and inflation; check manufacturer specs for exact mounted dimensions.

3) Can I compare two sizes?

Yes. Enter a second size to see diameter, ride height, and speed variance differences.

4) What does revs per mile mean?

It’s the number of tire rotations per mile at zero slip. It correlates with gearing and speedometer readings.

5) Why doesn’t my speedometer match the calculation?

Speedometers are calibrated for stock sizes and can have factory tolerances. Tire wear, pressure, and drivetrain slip also affect readings.

6) What air pressure should I use after changing size?

Use the vehicle placard as a baseline. If overall load index changes, consult the tire maker’s load/inflation tables.

7) Do I need an alignment after upsizing?

It’s recommended whenever changing wheels/tires to ensure proper toe and camber and to avoid uneven wear.