Tire Size
The tire size is written on the tire's sidewall.
P indicates a passenger (car-type) tire. Other options would be no P indicating metric sizing (essentially the same as P-sizing, which has its heritage in Europe) or LT for light truck. LT truck tires are designed for heavier loads and more rugged service conditions.
Width of the tire, in millimeters. The higher the number the wider the tire.
Aspect ratio - The height of the sidewall section compared to the width of the tire. Example: - If this number was a 50, then the tire section is half as tall as it is wide. Short sidewalls deliver crisp handling. Tall sidewalls give a smoother ride. For a specific tire width, the smaller this number, the shorter the sidewall.
Construction - R indicates radial construction. Unless you specify the other option, bias (which would have a D [diagonal] or B [belted bias] in this position instead of an R), you are purchasing a radial tire.
Wheel Size Designation - This indicates the distance across the "doughnut hole" of a tire, in simple terms. You must match wheel diameter and tire diameter. For example, a 15-inch diameter tire must only be mounted on a 15-inch diameter rim. A tire with a 15 size designation will not work on a 14" wheel, and vice versa. Improperly matching of wheel and tire size can cause serious injury or death during installation.
Service Description - Includes the load index (a number) and a speed symbol (a letter). About load index, remember: Keep the number the same as or greater than the original tires' load index. That number stands for a specific weight-carrying capability. Key is that the higher the number, the greater load-carrying capacity. So keep the number the same or higher, because your tires are matched to the weight of your car. Never choose a tire with a lower load-carrying capacity than the original equipment tire size.