Tire Diameter Calculator
Compare two tire sizes before changing wheels. See the diameter difference, whether it stays within the recommended 3%, and how your speedometer reading shifts.
How it works
A larger tire travels further per revolution, so the speedometer under-reads (shows less than actual speed). Staying within ±3% of the original diameter keeps speedometer, ABS and gear ratios within acceptable bounds.
Frequently asked questions
Why is 3% the usual limit?
Beyond ±3% the speedometer error grows, ABS/ESP calibration is affected and larger tires can rub. It is the de-facto industry rule of thumb for size changes.
A bigger tire makes my car faster — true?
It raises top speed slightly but reduces acceleration and makes the speedometer under-read. Net effect for most drivers is negative.