How Do You Determine What Size Tires You Need?


Quick Answer

To determine the tire size needed, use the group of numbers and letters on the sidewall of the tire that reflect the tire type, tire width, construction, rim diameter, load index and speed rating. Additionally, look for the maximum load also given on the tire's sidewall.

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How Do You Determine What Size Tires You Need?
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Full Answer

The numbers on the sidewall of the tire start with a letter that indicates the tire type. For example, the letter 'P' implies the tire is for a passenger car, and the letters 'LT' mean it is a light truck tire. The next three numbers indicate the tire width in millimeters. The width of the tire is measured from sidewall to sidewall.

The second two numbers on the tire's sidewall reflect the size of the sidewall. Measured in millimeters, this size extends from the top of the rim of the tire to top of its tread. The R following these two numbers is for radial that indicates that the layers of the tire run radially. The two numbers that follow the letter R indicate the rim diameter of the tire in inches. The rim diameter is measured from one end of the wheel to the other.

The last two numbers indicate the load index that reflects how much load the tire can carry. The maximum load the tire can carry is also given on the sidewall in pounds and kilograms. The last letter is indicative of the speed rating that reflects the tire's highest service speed.

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