Tyre size comparison calculator
Compare two tyre sizes, such as 205/55R16 and 225/45R17, for diameter and speedometer difference.
Check your tyre placard, load and speed ratings, and your state's vehicle modification rules before changing size.
How this calculator works
In a size like 205/55R16, 205 is the width in mm, 55 is the sidewall height as a percentage of the width, and 16 is the rim in inches. Overall diameter = rim × 25.4 + 2 × width × aspect ÷ 100.
Worked example: 205/55R16 is 631.9 mm across and 225/45R17 is 634.3 mm, a difference of +0.38%. At an indicated 100 km/h you'd be doing about 100.4 km/h.
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