Method
Sidewall mm = width×aspect/100; diameter in = rim + 2×sidewall/25.4; actual speed scales with diameter ratio.
Everyday worksheet
Tire Size Comparison Calculator
Compare two metric tire sizes for sidewall, diameter, circumference, revolutions, ride-height and speedometer change.
The calculation runs locally. Results include the intermediate values, unit conversions and assumptions needed to audit the answer.
Method, assumptions and practical use
How the Tire Size Comparison Calculator works
Sidewall mm = width×aspect/100; diameter in = rim + 2×sidewall/25.4; actual speed scales with diameter ratio. Inputs stay in this browser, and the result table exposes conversions and assumptions for independent checking.
Interpret the result
A larger rolling circumference travels farther per revolution and makes actual speed higher than indicated when replacing a smaller tire.
Check the assumptions
Matching diameter does not prove compatibility; verify wheel width, load/speed ratings, placard, pressure and physical clearance.
Local calculation
Everything runs in this browser. Inputs are not sent to an external calculator.
Rounding
Displayed values may be rounded for readability while calculations use full floating-point precision unless the tool explicitly uses exact integers.
Scope
Matching diameter does not prove compatibility; verify wheel width, load/speed ratings, placard, pressure and physical clearance.
Simple by design
Three steps to a clearer number.
Enter your details
Use realistic values in each field. You can change them anytime.
Calculate instantly
The formula runs locally, so there is no account or waiting time.
Use the result
Treat the answer as a practical estimate for your next decision.