Spare Tire Cover Diameter Calculation Guide
Step 1: Find Your Tire Parameter. It's Written On Your Tire Side
Step 2: Calculate Your Tire Diameter
If Your Tire Is Written With P225/65r17, A=225 B=65 C=17.
Tire Diameter=A*B/500+C*2.54 =225*65/500+17*2.54 =72.43cm
According To The Sizing Guide, You Can Choose The Right Size.