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Tire Size Calculator
Compare two tire sizes: overall diameter, width, sidewall height, circumference, revolutions per mile and speedometer difference.
How to use it
- Read the size on the sidewall, e.g. 265/70R17 = 265 mm wide, sidewall 70% of the width, 17 in wheel.
- Enter your current and new sizes.
- Keep the diameter change within about ±3% to limit speedometer error and fitment problems.
How it works
Sidewall = width × aspect ÷ 100 (mm). Diameter (in) = wheel + 2 × sidewall ÷ 25.4. Circumference = π × diameter; revolutions per mile = 63,360 ÷ circumference. A larger tire makes the speedometer read low: actual speed = reading × new diameter ÷ old diameter.
Always check load index, speed rating and clearance; your tire shop or vehicle placard is the authority.
FAQ
How much bigger can I go on tire size?
A common guideline is within ±3% of the original overall diameter; bigger changes can affect ABS, stability control, gearing and clearance.
What does 265/70R17 mean?
265 mm section width, a sidewall 70% as tall as the width (185.5 mm), radial construction, for a 17 in wheel - about 31.6 in tall.
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