You may feel bewildered by the array of letters and numbers you see when you read the sidewall of your tire.
However, the markings on the tires do follow a universal logic and convey specific information that is very important for comparing products and making decisions about safety.
Once you can decipher the code, you’ll have almost all the details about your tires you’ll need.
Your tire code, which usually has the largest print of all characters on the sidewall of tires (aside from the tire and brand name), has seven main components.
The image below shows an example, which we then break down point by point.
The first letter in the tire code lets you know the type of vehicle the tire is intended for. The most frequent type is P for passenger car, followed by LT for light truck.
The three-digit number immediately following the vehicle type letter(s) tells you how wide your tire is. This figure is in millimeters, and is the measurement from sidewall to sidewall at the tire’s widest point. In this example, the tire is 275 mm wide.
The aspect ratio indirectly tells you how tall your tire is. It is expressed as a percentage of the tire’s width. In the example code, the aspect ratio is 30, so the tire’s height is 30 percent of its width.
The optional letter following the aspect ratio indicates how the body of the tire is constructed. Standard construction for almost all consumer tires is radial ply, which is indicated in this example by an R. Other construction types could be B (bias ply) or D (diagonal).
Following the tire body construction letter is a two-digit number that tells you the diameter of the rims the tire is meant to be mounted on. This measurement is expressed in inches. In this example, the tire is designed for 19 inch rims.
The tire load index indirectly states how much weight a tire can bear. This number is not expressed directly in pounds or kilograms or any other unit for measuring weight. It is rather a numerical code that can be used along with a standardized reference table to look up the tire’s actual safe load, in pounds, at maximum inflation pressure. In this example, the number 96 means the tire can withstand a load of 1565 pounds.
The tire’s speed rating is also expressed indirectly, this time using a letter code. This letter can be used to look up the maximum speed the tire can safely withstand with a fully loaded vehicle (according to its load index rating). In this case, the letter Y means the tire is rated for sustained speeds up to 186 miles per hour.
Your tire’s sidewall may also show the maximum air pressure, a traction rating, and a treadwear rating, as well as the legally required DOT code, among other information. All of these aspects are explained in more detail below.
The DOT tire date code is a 7 to 13 character code that is legally required and is usually printed in smaller letters near the bead of the tire (where the tire meets the rim). Its first letters are DOT, which stands for “Department of Transportation” and indicates that the government agency has approved the tire. The last four numbers of the DOT code are often the most useful to car owners because they indicate the age of the tire. The first two digits of the last four numbers tell you the week the tire was manufactured, and the last two the year. For instance, a tire with a DOT code of 1119 was manufactured in the 11th week of 2019. This information is important because a tire’s performance and safety diminishes with age, even if the tire is not used, due to chemical breakdown. Other information included in the DOT code is place of manufacture, size, and tire type.
Tires may also contain text indicating the maximum air pressure to which they should be inflated. This pressure is stated in PSI (pounds per square inch). You should know that this pressure is not the same as the recommended pressure, which is specified in your operator’s manual or on the inside of your driver’s door. The maximum pressure is the most you can safely inflate your tires, but if you run your tires at that pressure, they will most likely wear out more quickly and cause you braking and handling issues.
In 1979, the U.S. implemented the Uniform Tire Quality Grading (UTQG) standards to measure different tire quality parameters and allow consumer to compare tires more easily. Manufacturers are required to mark the results of these tests on the side wall of their tires. The UTQG system covers three main components (traction, treadwear, and temperature), which are described in more detail below.
One component of the UTQG is the traction rating, or traction grade, which tells you how well a tire is able to stop on wet pavement. The best rating is AA, followed by A, B, and C. Most tires receive an A rating, but a high-performance tire would receive AA. This grade only refers to stopping power, not cornering, handling, or ability to prevent hydroplaning.
Another element of the UTQG is the treadwear rating, which tells you how quickly a tire’s tread wears out on a test track where all other variables are controlled. Most ratings fall between 200 and 500, using a scoring system devised to be able to compare tires based on a baseline value in the UTQG. Theoretically, a tire with a treadwear rating of 400 should last twice as long as one marked 200. In reality, many factors, such as your car’s alignment, tire rotation, and the kinds of surfaces you normally drive on can have a very big influence on how long your tread will last regardless of its rating.
The third element of the UTQG is a temperature grade. This grade can be A, B, or C, and it represents the tire’s ability to dissipate heat when rolling at or over a certain speed. A is the best rating (resists heat well at over 115 MPH), followed by B (100 to 115 MPH), and C (85 to 100 MPH).
Your tire may also contain a letter indicating the load range. Unlike the load index, this single number does not refer to a specific amount of weight that the tire can bear. Rather, it more generally specifies the toughness of the tire and the amount of air pressure it can hold. It can also be called the ply rating because tires used to be built with different layers of cords and fabric called plies, and the more plies, the sturdier the tire and the farther along in the alphabet the ply rating letter was. This type of construction is no longer used, but a tire with a load range of C, for example, is the equivalent of a 6-ply tire. The tire sidewall may also show information about the materials used to construct the tire’s sidewall and body. Additionally, you may see the letters M+S, which stand for mud and snow. This means the tire has some ability to handle these slick conditions. However, a true snow tire will also have a symbol of mountain peaks with snowflakes inside them.
Now that you know how to decipher the information on your sidewall, you can find tires for your size and driving style in Pirelli’s catalog.
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