Tire Size Calculator
Calculate tire diameter, sidewall height, and circumference from tire size notation.
Tire size notation like 205/55R16 encodes three key measurements: the tread width (205 mm), the aspect ratio (55% — sidewall height as a percentage of width), and the rim diameter (16 inches).
The sidewall height is calculated by multiplying width by the aspect ratio: 205 x 0.55 = 112.75 mm. The overall tire diameter adds two sidewalls to the rim diameter: 2 x 112.75 + (16 x 25.4) = 631.9 mm. The circumference determines how far the tire travels in one revolution.
This information is essential when changing tire sizes to ensure speedometer accuracy, proper fender clearance, and correct gear ratios. A general rule is to stay within 3% of the original diameter to avoid issues.