Why does tire size matter for speedometer accuracy?

Changing tire diameter changes how many revolutions cover a given distance, which can throw off your speedometer and odometer readings.

Tire Size Calculator

Compare tire sizes and diameter differences

Width (mm)

Aspect Ratio (%)

Rim Diameter (in)

24.97in

Overall Diameter

Overall Diameter = Rim Diameter + 2 × (Width × Aspect Ratio / 100) / 25.4

1Enter the tire's width, aspect ratio, and rim diameter (e.g. from "225/45R17").
2See the overall diameter, circumference, and revolutions per mile.

Example 1

Width=225mm, Aspect=45%, Rim=17in

Overall diameter ≈ 24.97 in

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