The size of a tire is usually represented by a sequence of numbers and letters printed on the side of the tire. The format of this sequence can vary slightly depending on the type and brand of tire, but it generally follows a standardized pattern.
The most common way to read the size of a tire is to look for a sequence of numbers and letters printed on the side of the tire. The sequence typically starts with a letter indicating the tire's intended use. For example, "P" stands for passenger car, "LT" stands for light truck, and "ST" stands for special trailer.
The next three numbers indicate the tire's width in millimeters, followed by a forward slash (/), which is followed by two numbers indicating the tire's aspect ratio (the ratio of the height of the tire's sidewall to its width). The next letter indicates the tire's construction type, which can be "R" for radial, "D" for diagonal, or "B" for bias.
The next two numbers indicate the tire's diameter in inches, followed by another letter indicating the tire's load index and speed rating. The load index indicates the maximum load capacity of the tire, while the speed rating indicates the maximum speed the tire is designed to handle.
For example, a tire with the size designation "P205/55R16 91V" would be a passenger car tire with a width of 205 millimeters, an aspect ratio of 55, a radial construction, a diameter of 16 inches, a load index of 91 (which corresponds to a maximum load of 1,356 pounds), and a speed rating of V (which corresponds to a maximum speed of 149 miles per hour).
How are tire sizes measured
Tire sizes are measured in a standardized format that uses a combination of numbers and letters to represent various aspects of the tire's dimensions and performance characteristics.The first number in the tire size represents the width of the tire in millimeters, measured from sidewall to sidewall when the tire is mounted on a standard rim and inflated to the recommended pressure.
The second number in the tire size represents the aspect ratio of the tire, which is the ratio of the height of the tire's sidewall to its width. This is expressed as a percentage of the tire's width. For example, if the tire's width is 205 millimeters and the aspect ratio is 55%, the height of the tire's sidewall would be 0.55 times 205, or 112.75 millimeters.
The letter following the aspect ratio indicates the tire's construction type. "R" indicates a radial tire, which is the most common type of tire today. "B" indicates a bias-ply tire, which is an older design that is less common today. "D" indicates a diagonal or bias-belted tire, which is a hybrid of the two.
The next number in the tire size represents the diameter of the wheel rim that the tire is designed to fit. This is measured in inches and represents the distance from one edge of the rim to the opposite edge, passing through the center of the rim.
The final letter in the tire size represents the tire's speed rating, which indicates the maximum speed the tire is rated to handle. For example, "S" indicates a maximum speed of 112 miles per hour, while "W" indicates a maximum speed of 168 miles per hour.
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