Questions
How the calculators work, which formulas they use, and where they stop.
Questions
Are these calculators accurate?
They are exact for the formulas they use, and every one is tested before it goes live. The limit is the input: tire sizes are nominal, and real tires vary by maker, tread depth and load, so measured figures can differ by a few tenths of an inch.
Why does my tire maker list a different diameter or revolutions per mile?
Makers measure a real tire, and revolutions per mile are measured under load, when the tire is slightly squashed. That makes the published revolutions per mile a little higher than the figure from the size code. For speedometer calibration, use the maker's spec for your exact tire.
Do these replace a tire shop or mechanic?
No. They are for planning and checking. Fitment, load ratings and safety systems should be confirmed by a qualified shop for your vehicle.
Do you store what I enter?
No. The calculations run in your browser and nothing you type is sent to a server.
Can I suggest a calculator?
Yes. Email [email protected] with the calculation you need.