Trip estimates

Tire Size Calculator

Calculate tire dimensions and how a new tire size affects speedometer reading. Use this Travel and transport tool to enter your numbers, review the result, and understand the key assumptions before making the next decision.

What you get
A focused calculator, clear explanation, common questions, and useful next tools.
Quick intro
Calculator
Result
Explanation
Common questions
Related tools

Calculator tool

How this calculator works
The result depends on the numbers you enter and the assumptions shown below.

Tire size format: Width/AspectRatio-RimDiameter (e.g., 225/45R17). Sidewall height = Width × Aspect/100. Overall diameter = (2 × Sidewall) + (Rim × 25.4) mm. Speedometer error = (new circumference − old circumference) / old circumference × 100.

Review the inputs carefully and treat the output as an estimate. For decisions involving money, taxes, health, law, or security, compare the result with trusted professional guidance when needed.

Frequently asked questions

Will changing tire size affect my speedometer?

Yes. A larger overall diameter means your car travels farther per wheel revolution, making the speedometer read lower than actual speed. A smaller tire has the opposite effect.