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By Tire Agent Staff
August 09, 2021
Tires have several numbers and symbols on the sidewall, and they can be a little mysterious if you don't know their meaning. Each number and symbol has specific meanings, and plus there are other key elements you should know about your tires!
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What do all the numbers and symbols mean? Here is a guide to understanding tire size meaning.
Every tire has 3 numbers that mean a specific size:
The first number measures the width and it looks something like this: [205/65 R 15]. The 205 on the tire means it is 205 millimeters wide looking at the tire head on.
The second number, 65, is the aspect ratio, which means that the height of the tire is 65% of the tire's width for this example. The bigger the aspect ratio, the larger the sidewall of the tire.
The last number, 15, is the rim diameter of the wheel that the tire will fit.
The tire letter meaning refers to the construction of the tire: R for radial, D for diagonal, and RF for run-flat.
Next to your tire size you will see a number and letter combination like 94H. The number “94” 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. Load index ranges from 0 to 150.
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.
Next to the load index there is a letter. In the example mentioned above, the “H” is the speed rating. This is the maximum speed sustainable for the tire. Each letter has a corresponding speed rating approved by the DOT (Department of Transportation) and the tire manufacturer.
Alphabetically, the speed rating increases as the letters advance A-Z -- EXCEPT for the letter H, which we'll explain in a minute. The most common speed ratings range from L (75 MPH) to W (168 MPH). High-performance racing tires speed rated 168 MPH or higher are marked ZR.
Originally, tire speeds were just S, H, or V (S being the slowest, H being the middle, and V being the fastest); over the years as tire speeds have evolved, for whatever reason, H has always remained the same, 130 MPH.
Your tires 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. In the example above, the tire was made in the last week (52) of 2010. DOT signifies that the manufacturer has complied with the Department of Transportations tire safety standards.
Additionally you will find letters and symbols that tell you more about the tires, although not all tires have the following letters and symbols.
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.
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.
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 sellable by retailers in compliance with EU standards. Not all tires sold in the U.S. have an S-mark.
P on a tire stands for passenger and means the tire was designed to be used on passenger vehicle types.
LT on a tire stands for light truck and means the tire was designed to be used on light and heavy-duty pick up trucks.
ST on a tire stands for special tire and means that the tires are designed for towing trailers with non-powered axels.
R17 on a tire means that the rim size needed would be 17". The "R" actually stands for radial, not rim and is the type of technology the tire uses.
The Z means that the tire has been tested over 186 mph
The R on a tire stands for radial and refers to the type of technology being used within the tire.