Letter And Number Designations On Your Tires: What They Mean
If you have ever had to replace a tire on your car, chances are that the technician asked you what kind of tire you need. You probably had to look for the numbers and letters on the tire, just above the hubcap. Reading off this series of numbers and letters, you might wonder what they stand for. Their designations are very specific and tell the tire and wheel technician exactly what kind of tires you need to replace.
The Letters on Your Tires
The very first letter on every tire designates the type of vehicle you drive for which the tire was made. For example, a "P" means "P-Metric" and also stands for passenger vehicle, "LT" means light truck, and no leading letter means it is probably a European Metric tire, which has different load-bearing requirements (e.g., think luxury Italian import vehicles). Almost all passenger vehicles made in the U.S. will have tire letter designations that lead with "P."
The next letter you will see in this stream of numbers and letters is often "R." If you think about this for a second, you can probably guess what "R" means. It means "radial," indicating that the wires and rubber layers inside the tire that help it keep its shape run radially around the tire.
The third and final letter in this series on your tires indicates how fast you are allowed to drive on these tires. There are multiple letter designations in this final spot, each with its own secret code for speed. For example, an "H" indicates that 130mph is the maximum speed you should drive on your tires. However, since there are no speed limits in the country that exceed 75mph, you could install tires with an E, F, or G speed rating too.
The Numbers
Each set of numbers designates something important about your tires as well. The first set of numbers following the first letter indicate the tire's width. This is important because you do not want to install a tire that is either too wide or too narrow on your rims. Doing so would ruin your vehicle's rims and ability to turn and brake effectively. If this number looks really large, do not let it intimidate you, since the number means "millimeters" and not inches or any other form of measurement.
The number after the slash is the tire's aspect ratio. It tells you how high the tire is compared to its width. It is a key indicator that identifies and separates tires of a similar width but different heights. The number following the "R" is the diameter of the tire, measured from side to side in inches.
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