How to Read Car Tires Types

If you want to make sure the tires you bought are the ones they put on your car, or if you're just curious about all those letters and numbers on the sidewall of your tires, it's easy to interpret them. All tires are required by law to bear these markings. Taken together, these markings will tell you, among other things, the size of the tire, how heavy of a load the tires can safely carry, and even give you an indication of how quickly the tires will wear out under normal use.

Instructions

1. Find the large raised lettering on the sidewall of your tire. It is usually located near the manufacturer's name. There will be a letter followed by a series of numbers. This is the code for your tire type. For this we will use the example: P215/65 R15 89H.

2. Determine tire type. The letter code is what defines the proper use of the tire. Tires for passenger cars begin with the letter "P." An "LT" designates the tire is for a light truck. A "T" indicates that the tire is a temporary spare. An "ST" indicates that the tire is for a trailer such as for a boat or generic hauling trailer.

3. Determine tire width. The next set of digits, up to the "/" designate the width of the tire. This is the measurement in millimeters of the tire's width from sidewall to sidewall. Our example tire has a width of 215 millimeters.

4. Determine aspect ratio. The number immediately following the "/" is the height of the tire's cross section as a ratio of its width. Our example tire bears the number 65, it means that the height of the tire's sidewall is equal to 65 percent of its width.

5. Determine construction method. Next you will find either the letter "R" or the letter "B." The "R" stands for radial construction, meaning the layers of material run across the tire's radius. The "B" stands for bias construction, meaning the layers of material run diagonally across the tire.

6. Determine wheel diameter. The number immediately following the construction method designates the diameter of the wheel in inches from end to end. Our example tire is 15 inches in diameter.

7. Determine load index. The number following the blank space after the wheel diameter is the load index, which is a code that indicates the maximum load in pounds the tire can support when it is inflated properly. Our example tire has a load index of 89, which indicates that it can carry a maximum load of 1,279 pounds. The higher the load index number, the greater number of pounds the tire can safely carry.

8. Determine speed rating. This letter corresponds to the maximum speed the tire is capable of according to the following: Q = 99 mph; S = 112 mph; T = 118 mph; U = 124 mph; H = 130 mph; V = above 130 mph. The maximum safe speed for our example tire is 130 mph. This is not a recommendation to exceed posted speed limits.

9. Determine DOT (Department of Transportation) compliance. A smaller "DOT" followed by the tire's serial or identification number -- up to 12 digits -- indicates that the tire complies with applicable DOT standards.

10. Determine UTQG (uniform tire quality grading system) rating. A tread wear rating of 100 is the baseline. Tires designated with a tread wear rating over 100 are better than average, tires with tread wear rating below 100 are poorer than average. For example, a tire with a 200 tread wear rating would wear twice as long as one rated 100. These grades are only valid for comparing different tires from the same manufacturer and are not valid for comparing tires between different manufacturers.

    Traction grades indicate the ability of the tire to stop on wet pavement as measured under controlled conditions. A is rated best, B is rated intermediate and C is rated acceptable.

    Temperature grades indicate how the tire resists heat generated by friction when tested under controlled conditions. This is a measurement of the tire's resistance to deterioration under sustained high temperatures. A is rated best, B is rated intermediate and C is rated acceptable.

Tips & Warnings

• Consult your owner's manual to determine the correct size of tires for your vehicle.