Tire Size Calculator
Convert a tire's width, aspect ratio and rim size into its sidewall height and overall diameter.
Overall diameter634.3mm
Diameter in inches24.97in
Sidewall height101.3mm
For a tire like 225/45R17, the sidewall height = section width × aspect ratio ÷ 100 = 225 × 45 ÷ 100 = 101.25 mm. The overall diameter = rim diameter (in mm: rim × 25.4) + two sidewalls = 17 × 25.4 + 2 × 101.25 = 431.8 + 202.5 = 634.3 mm, which is ≈ 24.97 inches. When changing tire sizes, keeping the overall diameter within about 3% preserves your speedometer accuracy.
Questions
How do I work out a tire's diameter from its size code?
From a code like 225/45R17, the sidewall is 225 × 45 ÷ 100 = 101.25 mm. The diameter is the rim (17 × 25.4 = 431.8 mm) plus two sidewalls: 431.8 + 202.5 = 634.3 mm, about 24.97 inches.
What does 225/45R17 mean?
225 is the tread width in millimetres, 45 is the aspect ratio (sidewall height as a percentage of width), R means radial construction, and 17 is the wheel rim diameter in inches.