How to Read the Speed Rating & Weights on Tires
Your tires are the most important part of your car, but not all tires are created equal. Tires are manufactured with various speed ratings and load indexes, and which type of tire you should buy depends on the type of vehicle you use and what you use it for. Knowing your tires' speed rating and the maximum weight they can carry will help you drive safely and get the most out of your vehicle.
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Instructions
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Examine the side of the tire that faces out when the tire is installed. The side of a tire is called a sidewall, and it will have the tire's brand and tire size printed on it. The tire size is a series of letters and numbers that provide information about a tire's dimensions and capabilities. An example of a tire size is: P195/60R15 87S.
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Find the last three digits of the tire size. In the example given above, the last three digits are: 87S. The first two digits give the load index; the letter that follows gives you the tire's speed rating.
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Examine the two digits that comprise the load index. The load index indicates the maximum load that the tire can support when it is properly inflated. However, the load index of 87 in our example does not mean that the tire can support only 87 lbs. Rather, the load index must be interpreted using a load index chart. Such charts can be found on the Internet (see Resources). Examining one of these charts, we find that a load index of 87 corresponds with a maximum load of 1201 lbs.
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Find the speed rating, which is the letter that follows the tire's load index. The speed rating tells you the maximum speed capability of the tire. When driving, the maximum speed of the vehicle is limited to that of the tire with the lowest speed rating. As with the load index, a chart must be used to correctly interpret the speed rating. In our example, the tire has a speed rating of S. Examining a speed rating chart, we find that S gives a maximum speed of 112 mph.
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Tips & Warnings
It is recommended that a speed-rated tire only be replaced with a tire that has an equivalent or greater speed rating. However, it is safe to use a tire with a lesser speed rating if you never drive at speeds near the limits of your speed-rated tires.
Speed ratings and load indices only apply to tires that have not been damaged, altered, under-inflated or overloaded.
Tire speed ratings do not imply that the vehicle can be safely driven at the maximum speed for which the tire is rated, especially under unsafe driving conditions. And regardless of the speed rating, it is NEVER recommended that you exceed legally posted speed limits.
References
Resources
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