The two-digit number is in inches and the most regular sizes are from 8” to 28”. If you want to know if a particular spare tire cover will fit to your wheels simply read the numbers off the sidewall of your current vehicle or trailer tire.

Tire width/section width/cross section are the first three tire numbers of the code, in millimeters. The measurement shows the distance from the widest spot of the inner sidewall to the same of the outer sidewall. Look for something like 185, 195 etc.

Aspect ratio/tire is the relation of the tire’s width and height in percent. So, 55 profile is 55% of the width, meaning the tire’s height is (taking the width of 205 mm) 112.75 mm or 4.4”. Without these numbers have a standard profile.