A tyre size such as 265/65R17 gives the width in mm (265), the aspect ratio of sidewall height to width (65%) and the rim diameter in inches (17). The overall diameter is the rim diameter plus twice the sidewall: 17 × 25.4 = 431.8 mm plus 2 × (265 × 0.65) = 344.5 mm, giving 776 mm. The circumference is π × 776 = about 2,439 mm, so the tyre turns about 410 times per kilometre. If you change tyre size, the speedometer reading changes in proportion to the diameter, so keep the overall diameter within a few percent of the original. Check the load and speed ratings and the legal limits for your state.

How to Calculate Tire Size Circumference & Diameter Converter (Step-by-Step)

Enter Tire Width (mm - e.g. 225): Input your target parameter value.
Enter Aspect Ratio (% - e.g. 45): Input your target parameter value.
Enter Wheel Diameter (Inches - e.g. 17): Input your target parameter value.
Apply Formula: Calculate using Diameter = (Rim × 25.4) + 2 × (Width × Aspect%) | Circumference = π × Diameter.
Review Results: View exact computed answers, metrics, and worked mathematical proofs.

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Frequently Asked Questions (FAQs)

What does 225/45R17 mean?

225 is tire width in mm, 45 is sidewall height as % of width, R is radial, and 17 is rim size in inches.

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