Tire Size Calculator

1. Tire 1: Stock size (e.g., 225/45 R17).
2. Tire 2: New size (e.g., 245/40 R18).
3. Compare: Diameter difference and speedometer error %.

The Tire Size Calculator compares the diameter, width, and sidewall of two different tires. Changing tire sizes effects your speedometer!

This tool tells you if your new speedometer reading will be faster or slower than reality.