Tire Size Calculator
Compare two tire sizes and see how the swap affects diameter, speedometer accuracy, and ground clearance.
Current size
New size
Diameter and tread width shown to scale.
How this is calculated
Overall tire diameter is the rim diameter plus twice the sidewall height (width × aspect ratio, converted from millimeters to inches). Speedometer accuracy and ground clearance both follow directly from the change in that overall diameter — a taller tire reads slower on your speedometer than your true speed, and adds roughly half its diameter increase in clearance.
Common questions
Will a bigger tire rub my fender?
Depends on suspension travel and offset, not diameter alone — a diameter change over roughly 3% is worth checking against your specific fender clearance.
What is "plus sizing"?
Going up a rim size while lowering the aspect ratio enough to keep overall diameter — and speedometer accuracy — nearly unchanged.
Part of Automotive Calculators