Measured in millimeters from the outer sidewall to the inner sidewall at the widest point when mounted.
Aspect Ratio
The ratio between the height of the sidewall and its Section Width, expressed as a percentage. The lower the number, the lower the "profile" of the tire.
Wheel Diameter
Most wheel rim diameters are measured in inches, and are known as "inch rim" sizes. These are found on most cars, vans, SUVs and light trucks. Some heavy trailers, van and trucks use a half-inch measure. In addition, some rims are measured in millimeters. It's very important that your tire and wheel diameter match exactly. This should be confirmed before installation.