Understanding Tire Sidewall Codes!
What does all the numbers mean? Each section of small print on a tire's sidewall means something! Car, Truck and SUV tire ratings are described by an alphanumeric code which is generally molded into the side-wall of the tire. This code specifies the dimensions of the tire and some of its key limitations such as load bearing ability and maximum speed. There are two important parts to your tire size. The size itself and the service description.
Tire Size and Service Description
Car tires and Truck tires are made up of three numbers. The first number is the tire width and is displayed in millimeters. The second number is the aspect ratio, which is the sidewall height listed as a percentage of the width. Followed by an R for Radial. The last number is the rim size or diameter in inches. When determining what tire you need all three of these numbers width, aspect ratio and rim size should match exactly.
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The tire Service Description is made up of two parts. The first is a two or three digit number indicating the load rating or index of the tire. This determines the weight the tire can carry. When replacing tires, you should select a tire with the same or higher load index than what is listed on the tire information placard.
Following the load index number is a letter called the speed ratings. This letter determines the top speed this tire can handle. Higher speed ratings usually mean better handling. You should select a speed rating that indicates the same top speed or higher than what is listed on your tire information placard.
The P designates that the tire is a passenger vehicle tire. Some other designations are LT for light truck, and T for temporary, or spare tires. The R designates that the tire was made using radial construction. Tire traction is rated AA, A, B or C, with AA at the top of the scale. The tire temperature ratings are A, B or C. The rating is a measure of how well the tire dissipates heat and how well it handles the build up of heat. The load rating is a number that correlates to the maximum rated load for that tire. A higher number indicates that the tire has a higher load capacity. The letter that follows the load rating indicates the maximum speed allowable for this tire. An S indicates that the tire can handle speeds up to 112 mph. M&S for Mud and Snow. TL means tubeless.
Some tread designs are designed to perform better when driven in a specific direction (clockwise or counter-clockwise). Such tires will have an arrow showing which way the tire should rotate when the vehicle is moving forwards. It is important not to put a 'clockwise' tire on the left hand side of the car or a 'counter-clockwise' tire on the right side.
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