Tire Size

The tire markings on the sidewall of the tire physically describe the tire.

The letter P means it is a tire for a passenger vehicle tire. LT means it is for a light truck. If there is no P it indicates metric sizing (essentially the same as P-sizing, as used in Europe). LT truck tires are designed for heavier loads and tougher service conditions.

A number in front of a slash-mark, such as “185/” indicates the width of the tire, in millimeters. The higher the number, the wider the tire.

Aspect ratio

After the slash, a two digit number states a percentage, or ratio of the height of the sidewall section compared to the width of the tire. For instance, if the number is 50, then the tire section is half as tall as it is wide. Given a specific tire width, a smaller number means a shorter sidewall. Short sidewalls give quick handling. Taller sidewalls deliver a smoother ride.

Construction

The letter R shows you are purchasing a radial-construction tire. If there is no R, or if there is a D (for diagonal) or a letter B, the tire is of the belted bias type of construction.

Wheel Diameter and Tire Size

Another two-digit number shows the width of the “doughnut hole” of a tire. For example, a 15 means that this 15 inches of the tire must match the 15- inch diameter of the wheel rim. A tire with a 15 size-designation will not work on a 14? wheel, and vice versa. Improper matching of tire size and wheel size can cause serious injury or death during installation.

Service Description

A marking such as 82H represents the load index (a number) and a speed symbol (a letter). This is important: Keep the load index number the same as or greater than the original tires’ load index. Know that the higher the number, the greater is the vehicle load-carrying capacity. That number is a code for the maximum weight the tire is designed to support. So keep the number the same or higher, because your tires are matched to the weight of your vehicle. Never choose a tire with a lower vehicle load-carrying capacity than the Original Equipment tire size. The letter H is a code for the maximum sustained speed rating of the tire. Specifically, an H code is for a max. speed of 130 MPH.