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January 10, 2021

What Do the Numbers on a Tire Mean

If you've ever taken a close look at the side of your vehicle's tires, you've probably noticed a lot of printed numbers and letters that, to the untrained eye, don't make any sense. But a little education can change your perspective, helping you read these numbers and understand the information they provide to car owners, mechanics, and tire experts.

What do the numbers on a tire mean? While the codes and combinations of numbers may look confusing, they're actually well-organized and offer a lot of useful information related to the production and performance of your tires. Here's a guide to reading and understanding these numbers.

What Does the First Number on a Tire Mean?

The first number on any tire—which is actually a combination of letters and numbers—gives you all the information you need related to your tire's size. Here's how to read tire size in this format: 

    The "P" at the start of the first set of numbers indicates that the tire is a passenger vehicle tire. The following three numbers represent the width of the tire at its largest point, in millimeters. The number 235, for example, means that the tire is 235mm wide at its widest point. The number after the slash represents the tire's sidewall height, as a percentage of its width. The number 65 would suggest that the height of the sidewall is 65 percent the size of the tire's width. The following letter refers to the tire's type of construction. Most passenger tires will feature an "R", which denotes a radial construction. The final number in this sequence identifies the size of the wheel that fits the tire. The number 18 corresponds to an 18-inch wheel.

Guidelines for Reading Tire Date Codes

Wondering how to tell when a tire was made? The answer can be found in the tire identification number, which is a unique code given to each manufactured tire. Each Department of Transportation manufacturing code is 11 or 12 characters long and features a mix of letters and numbers.

The first seven or eight of these characters are used to track the manufacture of tires. The last four digits are where you can find the date of manufacture: The first two numbers represent the week of the year the tires were manufactured, and the last two numbers represent the year. A code of 4215, for example, indicates that the tire was manufactured in the 42nd week of the year 2015.

This is helpful when tracking the age of your tires, and when to purchase replacements: Most tire manufacturers recommend replacing tires once they're more than six years old.

How to Read a Tire: The Rest of the Numbers

The size of your tires and their date of production aren't the only numbers featured on your tire. Other information printed onto the tire offers valuable insights into the specifications and performance design of the tire. 

Those numbers include the following: 

  • Load index and speed symbol: Right after the tire width and aspect ratio numbers, these numbers correspond to the load-carrying capacity and maximum speed recommendation for those tires. The load index is presented as a number, and the speed symbol is a letter. Each number and letter corresponds to a carrying capacity and speed limit that you can find on corresponding load index charts and speed symbol charts. The combination 90H, for example, corresponds to a load capacity of 1,323 pounds, and a top speed of 130 miles per hour. 
  • Mud and snow rating: On some tires, the letter combination "M + S" will follow the load index and speed symbol. This distinguishes the tires as having mud and snow capabilities, which buyers in certain climates may prefer. Keep in mind that this designation does not mean the tires function as snow tires. If you're looking for heavy-duty traction in snow, you'll want to purchase tires made specifically for that purpose.
  • Maximum tire pressure: This number represents the highest amount of air pressure you can add to a tire before it damages the tire itself. Keep in mind that this maximum number is not the recommended tire pressure to optimize your vehicle's performance. You can find the recommended tire pressure in your owner's manual.

When you're changing tires and performing maintenance on your vehicle, it helps to have quick and easy access to the specifications of your tires. Once you know how to read tire numbers, you can quickly gather this information from your own vehicle's tires, and make sure you're properly using this information to maximize your performance and safety.

And when it comes time to buy replacement tires for your vehicle, you can reference this information to easily pick out a matching set.

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