Tire Size Calculator
Compare two P-metric tire sizes (width / aspect / wheel diameter). See diameter, circumference, and how much your speedometer will be off.
Inputs
How it works
Sidewall height (mm) = width × aspect ÷ 100. Diameter (in) = wheel + 2 × sidewall ÷ 25.4. The percentage change is how far off your speedometer will read.
Frequently asked questions
What do the numbers on a tire mean?
225/45R17 = 225 mm wide, sidewall is 45% of width tall (101 mm), fits a 17-inch wheel. 'R' means radial.
Why does size affect the speedometer?
The odometer counts wheel revolutions × programmed circumference. Bigger tires travel farther per revolution, so the speedo under-reports.
How much difference is safe?
Stay within ±3% of stock diameter. Bigger changes can trigger ABS/traction warnings and affect ground clearance.
Do wider tires wear faster?
Not necessarily — wear is dominated by rubber compound, alignment, and inflation, not width.
Will a plus-size wheel void my warranty?
Usually no, but check your manufacturer's list of approved sizes for TPMS and load rating.