How to Read a Tire Sidewall

If you have ever had to order new tires, wanted to know how old your tires are, or anyone has ever asked you what size tires you have, this article is for you.

Flashlight

The first letter on the tire indicates its type. For passenger cars, you'll see a "P," standing for "Passenger." If it's a tire for light trucks, it might start with "LT" for "Light Truck." This distinction is crucial because it sets the foundation for understanding the tire's intended use and load capacity.

Following the tire type, you'll see a series of numbers and letters which represent the tire's size. For example, in a marking like "P225/45R18," the "225" denotes the tire's width in millimeters from sidewall to sidewall. The "45" is the aspect ratio, a percentage that describes the height of the tire's sidewall relative to its width. The "R" indicates the tire's construction type, with "R" standing for radial. Lastly, "18" tells you the wheel diameter in inches, indicating the size of the wheel the tire is intended to fit.

Near the end of the tire's sidewall markings, you'll find a load index and speed rating, often looking something like "104W." The load index, "104" in this case, is a numerical code that correlates with the maximum weight the tire can support when properly inflated. The higher the number, the more weight it can bear. The speed rating, represented by a letter "W" here, indicates the maximum speed at which the tire can safely operate when under load. Speed ratings range from A (the lowest) to Y (the highest), with each letter signifying a maximum speed in miles per hour.

Beyond the basic size, type, load index, and speed rating, tires may have other markings indicating special features or certifications. For example, "M+S" stands for mud and snow, indicating the tire's suitability for all-season use. The "DOT" symbol signifies that the tire complies with all applicable safety standards established by the U.S. Department of Transportation.

The tire’s manufacturing date is encoded in the final four digits of the DOT code, usually found in a separate oval shape on the sidewall. The first two digits represent the week of manufacture, and the last two digits signify the year. For example, "3219" indicates the tire was made in the 32nd week of 2019.