What are the numbers on the side of my tires?

November 30, 2018

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Tires have several numbers and symbols that are located on the sidewall and they can be a little confusing. Here we explain what each number and symbol means, where you will find them, and we breakdown other key elements for you to know about your tires!

Let’s start with the numbers

Size: Every tire has a specific size and it will look something like this [235/55R17]. The first number “235” is the width of the tire in millimeters if you are looking at the tire head on. The second number “55” is the aspect ratio. In this example, it means that the height of the tire is 55% of the tires width. The bigger the aspect ratio, the larger the sidewall of the tire. R stands for radial, and the last number “17” is the rim diameter of the wheel that the tire will fit.

Load Index: Next to your tire size you will see a number and letter combination like [103W]. The number “103” is the load index. This is the number relative to the weight capacity of the tire. The higher the number, the greater the load carrying capability of the tire.

If you are replacing your tires, they have to be the same or higher load index, never lower. For example, if your current load index is 103, a tire of the same size with a load index of 112 would work for you, but not a tire of the same size with a load index of 94. If you replace your tires and the new ones have a lower load index, the tire has a high likelihood of bubbling and eventually blowing out.

Speed Rating: Next to the load index there is a letter. In the example mentioned above, the “W” is the speed rating. This is the maximum speed sustainable for the tire. Alphabetically, the speed rating increases as the letters advance A-Z. For example, a speed rating of “W” means that the tire is approved for speeds up to 168 MPH. If you are looking at a tire with a speed rating “S” the tire is approved for speeds up to 112 MPH. Each letter has a corresponding speed rating approved by the DOT (Department of Transportation) and the tire manufacturer.

Week and Year of Production: Your tires will also have a number that indicates when the tire was made. This identification can be thought of as somewhat of a birth certificate for your tire. Beginning with DOT there is a combination of letters and numbers that will end in a 4-digit numerical code. For example, if your tire reads [DOT CPEX 3ET 0311] the tire was made during the 3rd week of the year 2011. Another example, [DOT TBN1 K650 1518] indicates the tire was produced in the 15th week of the year 2018. DOT signifies that the manufacturer has complied with the Department of Transportations tire safety standards.

Understand the symbols

Three-Peak Mountain Snowflake (3PMSF): If you see the three-peak mountain snowflake symbol on the sidewall of your tire, this indicates that they are rated for severe snow and ice. The symbol is identified by a snowflake surrounded by a 3-peak mountain zig-zag shape. If your tire has the 3PMSF symbol it meets the requirements of snow traction performance and has certified approval for severe winter conditions.

E-Mark: The E-Mark, found on the sidewall of the tire designates that the tire meets the minimum EU and international standards relating to the size, load index and speed rating of the tire. This marking confirms that testing has met adequate performance regulations. Not all tires sold in the U.S. have an E-mark.

S-Mark: The S-Mark, also found on the sidewall, means that the tire has met “sound approval” relating to the road noise produced by the tires. All new tires produced since 2011 must have an S-Mark rating to be saleable by retailers in compliance with EU standards. Not all tires sold in the U.S. have an S-mark.


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