What Do the Letters and Numbers on My Tire Mean?

That’s a great question, and while the answers are ultimately pretty simple individually, there’s quite a lot of information provided overall. Whether you’re looking to get new tires at a tire shop near you, like McCluskey Chevrolet, or you’re sitting in a parking lot waiting for an Uber and wondering about the esoteric symbols on the side of a tire close by, we’re here to answer all of your questions. Essentially, those numbers and letters provide you with information about that tire, including when it was made, its type and size, as well as how much weight it can handle on it without being damaged. If you need new tires and have a shop you trust, then your mechanic is going to figure all of this out for you. Still, it’s never a bad idea to understand what things are so you can double-check someone’s work to ensure your car has the right tires.

To keep things simple, we’ll take this one step at a time and look at each part of the code on your tires, beginning with information on the outside closer to the tread of your tires, then we’ll look at the inner writings too. For starters, let’s consider a tire that says something like, “P215/65R15 95H,” and see what that all means.

Manufacturer Name

Before we get into the various codes on your tires, you’ll most likely notice the manufacturer name and any particular model name on them. For example, your tire might say, “Goodyear,” “Bridgestone,” or one of a number of other manufacturers. They might also provide a description or model name they like to use, which can be helpful if you need a new set of tires and want to match them to what you’ve been using.

Type or Service Description

Now back to that code, the first part of it is a letter that indicates the type of tire it is or the sort of vehicle it’s made for. The majority of tires you’ll see on cars for consumer use will have a “P,” which indicates it’s a passenger car. Other codes include “LT” for light trucks, “ST” for tires designed for use on special trailers, and a “T” to indicate temporary spare tires. These codes are for American vehicles and tires––tires sold in Europe use a different system.

Tire Width

After the type letter, you’ll find three numbers: in our example, it’s “215.” This number indicates the width of the tire from one sidewall to the other, measured up from the edges and across the tire’s tread. This number is measured in millimeters, and a larger number indicates a wider tire. So for our example, we’re looking at a passenger tire that measures 215 mm in width.

Tire Aspect Ratio

This next part is going to be needlessly confusing, but we didn’t invent this system. Following the width of the tire, you’ll find a slash that separates it from the next two numbers, which indicate the aspect ratio of the tire. Specifically, this refers to the height of the tire from the edge of the sidewall to the surface as a percentage of the overall width of the tire. In other words, in our above example, the 65 means that the height of the tire is 65% of the overall tire width (the 215 mm from before). The larger the aspect ratio, the bigger the tire’s sidewall will be. There are reasons for differences in sidewall size, such as short sidewalls designed to help improve handling and steering responsiveness.

Construction Type

Following the aspect ratio, we find another letter that indicates the type of construction used in making the tire. In this case, the “R” in our example means these are radial tires; the internal construction of the tires uses a radial-ply design. You can find some tires that use a bias-ply construction, indicated as B on the tire, but the vast majority of tires in use will have an R here for radial-ply.

Wheel Diameter

The last number in this part of the code indicates the size of the wheels that the tire is designed for, measured in inches. So the “15” in the example above indicates that these tires are made to fit onto 15-inch wheels––this should always match the size of the wheels on your vehicle. The tires can be much larger than the wheels, but they still need to be designed to fit securely onto the wheels, so the code should match.

Load Index

The final part of this outer code starts with a two or three-digit number that indicates the load index for the tire that you’re looking at. This shows the maximum amount of weight the tire can handle, but it’s not a direct value––the number is a code you can look up on a Load Index Chart to see the amount of weight the tire can support. In the example of “95,” the chart shows us that the tire can handle up to 1,521 lbs of weight. Keep in mind that this is per tire, so with four of them on your car, they can handle up to 6,084 lbs of total weight.

Speed Rating

After the Load Index number, we find a final letter that indicates the speed rating of the tire. Again, you need to look up what this means on another chart, as there are numerous letters you can find on tires, including S, T, U, and V. In our example, the “H” means the tire can handle speeds up to 130 mph safely. This doesn’t mean you should drive at 130 mph, but if your vehicle got up to that speed, the tires could handle it without exploding.

Treadwear, Traction, Temperature Grades

Along the outer edge of your tire, but not part of the previous code, you’ll also find information about the treadwear for the tire and its traction and temperature grades. The treadwear number indicates how durable the tire is based on testing by the manufacturer against an industry standard. A baseline number of 100 is used for the industry standard––something rated at treadwear 150 would be expected to last 50% longer than that, while a treadwear rating of 75 might only last about 75% as long as the industry standard.

The Department of Transportation (DOT) has a Uniform Tire Quality Grading (UTQG) system for traction and the temperatures a tire can handle. The traction grade goes from C on the low end to B, then A, and then AA for the best traction possible. Similarly, for temperature grade, a C indicates it can handle temperatures at speeds between 85 and 100 mph, while a B can handle between 100 mph and 115 mph, and an A rating can handle the high temperatures of traveling faster than 115 mph. This is a separate consideration from the speed rating, which is about the durability of the tire and how it handles the pressure on it at high speeds.

DOT Code

You’ll find a code on every tire following the letters “DOT,” which is essentially a tire identification number. This can be used for things like recalls or to identify where a tire was made. The last four digits of this code always indicate when the tire was made, expressed as the week and year. For example, a DOT code ending in “1320” would’ve been manufactured in the 13th week––about the end of March––of 2020.

Maximum Inflation Pressure

With all of this other information, you’ll also find an indication of the maximum inflation pressure that the tire can handle, measured in PSI. It’s important to note that this is NOT the pressure you should fill it to or the recommended tire pressure for your vehicle––you’ll find that information in your car’s owner’s manual or on its doorjamb. This simply indicates the maximum pressure it can be filled to without bursting. You should always operate your vehicle with the tires at the recommended pressure to ensure the best performance and control.

Know You Know How to Read Your Tires

While there are a lot of numbers and letters to consider, reading your tires isn’t that difficult. Now that you know how to read your tires, you can make sure the right ones are on your vehicle. You may even be able to impress your mechanic by giving them the exact specs for your tires the next time you go to get them replaced.