Compare two tire sizes — will they fit & how does your speedo change?
This tire size calculator converts a tire size such as 225/45R17 into its real
overall diameter, sidewall height, circumference,
and revolutions per mile — and compares two sizes side by side. It tells you the
percentage change in diameter and how your speedometer reading shifts, so you can
judge whether a new size will fit. Free, private, in your browser.
In 225/45R17: 225 is the section width in millimeters, 45
is the aspect ratio (sidewall height = 45% of the width), and 17 is the wheel diameter
in inches. Overall diameter = wheel + two sidewalls. A safe upgrade usually keeps the new diameter within
about 3% of the original to avoid speedometer error and rubbing.
Sidewall (mm) = width × aspect ÷ 100. Overall diameter (in) = wheel + 2 × sidewall ÷ 25.4. Circumference = π × diameter. Revs per mile = 63,360 ÷ circumference (in). If your speedometer reads a speed with the old tire, true speed = reading × new diameter ÷ old diameter.
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<p>Free <a href="https://snaptoolsuite.com/tire-size-calculator/">Tire Size Calculator</a> by Snap Tool Suite</p>See it live: view a real embed example →
225/45R17 = 225 mm width, 45% aspect ratio (sidewall = 45% of width), 17-inch wheel. This tool turns that into real dimensions.
Yes — a bigger diameter reads slow, a smaller one reads fast. Stay within ~3% diameter change to keep it accurate.
Yes. 100% free, everything runs in your browser.
🔒 Everything is calculated in your browser. We don't store or sell your data.