Everything you need to know about a tire that's been manufactured for use in the United States and in most European countries can be found in the tire code. There are actually two codes that can be found on tires manufactured for use in the United States: the Department of Transportation (DOT) Code and the manufacturer's tire code, which possesses varied information about the tire's specifications. The tire code will vary from tire to tire, based on size, applicable vehicles, tire construction, tire usage, and materials.
There are two organizations responsible for setting standards within tire codes. Within Europe, the European Tyre and Rim Technical Organization is the responsible party. Within the United States, The Tire and Rim Association sets standards, while various government agencies, including state and federal Departments of Transportation, enforce quality and standards for driver safety and competitive equality.
What is the Tire Code?
When you take a look at the sidewall of any tire, you see a series of letters and numbers separated by various spaces and characters. Each of these numbers and letters stands for something. At first glance, the tire code may mean little to you aside from the size of the tire. After visiting RightTurn.com, you'll know what the entire code signifies.
Glossary of Tire Code Symbols
The first thing listed on the tire side wall is the name of the tire model. Following the name, the tire code begins with a letter: P - Passenger Car, LT - Light Truck, T - Temporary/Spare, ST - Special Trailer.
After the first letter, there are a series of numbers. One example is 205/55. The first number represents the width of the tread from the outer edge of each shoulder, measured in millimeters. The second number represents the height of the sidewall expressed as a percentage of the tire's width. In this example, the profile, or sidewall, is 55% of 205 millimeters.
The next letter represents the type of tire construction, or the construction style, used beneath the tread pattern: R - Radial, B - Bias, D - Diagonal. While most tire codes include this letter, some do not.
The next number listed is the size of the rim that the tire will fit on. Considering the earlier example, if the tire code reads 205/55R16, then the tire is made to fit a 16 inch rim.
Additional Tire Code Information
After the size and construction information, including the size of the wheel, there are sometimes additional numbers listed, potentially a three-character code. The first number represents the tire's load index. This code may be followed by a letter which is representative of the speed rating. For example: 86Z.
Additional information may also appear. For example, if the letters M+S are visible, it stands for Mud and Snow. Check out our article explaining the benefits of Mud and Snow tires. After all of the information, the tire brand is listed boldly, with any applicable company designs.
Putting everything together from the examples above, you have a hypothetical tire which would read as such: Tire Model P205/55R16 86Z M+S Goodyear.
Having a better understanding of the tire code will help you as you shop for tires. You can truly take control of the buying process because you know exactly what can fit on your vehicle and what can't. Fit is just one aspect of tires, and the more you know, the better you can choose a tire that fits your driving environment and style. For example, you wouldn't need a tire with a Z speed rating if you commute 5-10 miles daily at 35mph. This tire would be less than optimal and is the kind of tire that you can avoid if you understand the code on your current tires.
One word of caution: if you've replaced the tires that originally came on your vehicle, you'll want to double-check with your dealership to ensure the replacement tires are in fact the best ones for your vehicle. Unfortunately, not every tire seller is trustworthy.