Tire Size Comparison Calculator
Compare tire diameter, circumference, ride height, and speedometer change.
Calculator guide
Comparing tire diameter and ride height
This calculator compares two metric-format tire sizes to show nominal diameter change and the resulting static ride-height change.
Inputs and calculation
- Section width in millimeters, aspect ratio, and wheel diameter for the current and proposed tires.
Nominal diameter = wheel diameter + 2 × (section width × aspect-ratio fraction), with wheel and sidewall dimensions converted to the same unit.
Diameter change = (new diameter ÷ current diameter − 1) × 100. Ride-height change is half the diameter difference.
How to interpret the result
- A taller tire raises static ride height and travels farther per revolution, effectively lengthening gearing. A shorter tire does the opposite.
Assumptions and limits
- Sidewall markings describe a nominal size. Actual mounted diameter varies by tire model, rim width, pressure, load, wear, and growth at speed.
- Check manufacturer dimensions and chassis clearance before choosing a tire; this comparison does not model width or offset clearance.
Example: 245/40R17 to 255/40R17
The nominal diameter grows from about 24.7 to 25.0 inches, a 1.3% increase, and static ride height rises about 0.16 inch.
Keep tire changes with the setup
TuneWorks connects tire size, setup notes, sessions, and logs so changes are easy to review.