Tire Size Calculator
Compare nominal tire and wheel dimensions. The diagram helps explain changes; actual vehicle fit still needs checking.
Runs in your browser — nothing is uploaded—
Details
How to use Tire Size Calculator
- Enter your values — the unit for each field is shown next to it.
- The result updates instantly as you type.
- Copy the results, or change inputs to compare scenarios.
Formula & assumptions
Diameter = rim inches × 25.4 + 2 × width × aspect / 100
Circumference = π × diameter
Actual speed = indicated speed × new diameter / old diameter
Example: 205/55R16 → 225/45R17 changes nominal diameter from 631.9 to 634.3 mm.
Questions
Does a matching diameter guarantee fit?
No. Suspension, brakes, bodywork, alignment, manufacturer dimensions and vehicle-specific limits must be checked. Nominal calculations are a starting point.
How is backspacing estimated?
Nominal wheel width is measured between bead seats. We assume overall rim width is one inch wider, so backspacing = (width + 1 inch) / 2 + offset. Actual lip dimensions vary.