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Tire Speed Ratings 101

tire ratingsOn the side of your tires you will see several markings. These include the recommended tire inflation pressure, the size of your tires, and your tires’ speed rating and load rating. Understanding what these numbers mean is crucial when you are buying used tires because this affects the safety of you and your vehicle.

What Is A Tire Speed Rating?

The tire speed rating indication can be found as a specially marked letter of the alphabet on the sidewall of your tire. The speed rating of a tire refers to the exact MPH (miles per hour) that the manufacturer expects the tire to perform at for a long period of time without coming apart. In other words, if a tire is rated “S”, then the tire will perform for an extended period of time at 112 MPH.

The official tire speed rating system, as used in the United States, begins at A1 (a maximum MPH of 3) and ends at Y (over 186 MPH). Since the adoption of this speed rating system, additional ratings have been added so this is why letters like Z and Y do not have max speeds that simply increase in numerical order.

speed rating chart

What Does “Load Index” Mean For Passenger Car Tires?

The load index on a passenger car indicates the maximum load that the tire can carry. For example, a tire on a passenger car that has a load index of 100 will be able to carry a maximum of 1,764 pounds (nearly a ton). The tire load index code runs from 0 (99 pounds) to 150 (7,385 pounds). If you are crunching numbers in your head and wondering what type of load rating you need for the tires on your car… don’t forget, your car has 4 tires that each share the weight of your vehicle. Take your vehicle’s weight and divide by 4 to figure out what kind of tire you need.

P Tires vs. LT Tires

P tires are meant primarily for passenger vehicles. This can mean anything from compact cars to family SUV’s to light passenger trucks. P tires are marked with a special serial number that always begins with a “P”. This “P” signifies that the tire is a “P-metric” size. The term “P-metric” means that the specific size category is one that was originally formulated in Europe.

If the tire is marked with “LT”, this will refer to the tire being intended for “Light truck-metric” vehicles. This usually means a vehicle that carries a heavy cargo load, such as a full sized moving van, or a truck that hauls a large trailer behind it. This rating can include full sized pickup trucks, as well as any other vehicle short of an 18 wheeled tractor trailer.

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