Calculate tire diameter, circumference, revolutions per mile, and speedometer error when switching tire sizes. Confronto OEM and aftermarket tire specs instantly. Puro client-side — no data sent a servers.
This tire size calculator helps you compare original and aftermarket tire dimensions. It computes overall diameter, circumference, sidewall height, and revolutions per mile — plus the speedometer error you can expect when switching a a different tire size. All calculations happen in your browser; no data is uploaded anywhere.
Overall diameter = (2 × section width × aspect ratio ÷ 100) + rim diameter. The section width is in millimeters, and the rim diameter is in inches. For example, a 225/45R17 tire has an overall diameter of approximately 634.3 mm or 24.97 inches.
Speedometer error is the difference between the speed shown on your dashboard and your actual speed. When you install a larger tire, your speedometer reads slower than your actual speed. When you install a smaller tire, it reads faster. This is because the vehicle's speed sensor is calibrated for the original tire circumference.
Generally, tire experts recommend staying within ±3% of the original tire diameter a maintain safe handling, accurate speedometer readings, and proper clearance. Larger changes may affect ABS, traction control, and odometer accuracy. Always consult a tire professional before changing sizes.
225/45R17 is a standard tire size notation: 225 = section width in millimeters, 45 = aspect ratio (sidewall height is 45% of the width), R = radial construction, 17 = rim diameter in inches.