The best explanation of tire descriptions is by example. Consider the following tire description : P205 / 60R / 16 / 97H
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P Indicates that the tire is intended for passenger vehicle use. LT would indicate the tire is for Light Trucks.
205 Indicates the width of the tire in millimeters. 60 Describes the aspect ratio of the tire - in other words, how "thick" or "thin" the tire is relative to the section width. In this example, the tire would have a "thickness" of 60% of its width, or 123 millimeters.
R Indicates a Radial tire. This refers to the way the tire's ply cords are placed during manufacturing.
16 Refers to the wheel diameter a tire is intended for, in inches.
97 refers to the tire's load rating, and H is the tire's speed symbol.
For a more in depth explanation of Sizes Click Here