What do the numbers on my vehicle’s tires mean?

January 25th, 2021 by

a man inspecting a vehicle's tireTire sidewall number explanation 

What do the numbers on your vehicle’s tires mean? The number on a tire’s sidewall is an identifying number, which indicates certain characteristics of your tires. This number can be used for buying new tires, as long as you know what each part of it means. Keep reading below for a detailed tire sidewall number explanation. 

What does the first letter of a tire-number indicate? 

The first letter of the tire sidewall number identifies the type of tire that you have. Most of the tires you see should have a “P” as the first letter, which indicates that they are made to certain standards in the United States. They are approved as passenger vehicle tires. 

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What are all the components that make up the number on a tire? 

There are quite a few components that make up the number on your vehicle’s tires. The four main parts of a tire sidewall number are the tire width, aspect ratio, construction, and wheel diameter. Let’s go over what each of these means. 

  • Tire Width: The tire width is the first number directly after the first letter. It indicates the width of the tire measured in millimeters. It will be a three-digit number, as it indicates the width from sidewall to sidewall.  
  • Aspect Ratio: The aspect ratio is the ratio of the tire’s cross-section compared to its width. This number represents a percent, so if the number is 70, then its cross-section is 70 percent the width. This number directly follows the tire width, separated by a slash. 
  • Construction: The construction is represented by another letter, which will come towards the end of the tire sidewall number. Different letters mean different things. For the most part, you should know that an “R” stands for Radial, which means that the layers on the tire run radially. 
  • Wheel Diameter: The wheel diameter is right after the construction letter. This number represents the size of the wheel in inches, from one end to the other. This will be a two-digit number as wheels usually fall around 15 to 20 inches. 

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