Categories: How toTires

How to Read a Tire Sidewall – Car and Truck

A tire’s sidewall has a plethora of information listed. This article will illustrate how to decipher the majority of the information listed on the sidewall. This article will also show how to convert the more common metric sizing method into inches for the overall height, width, and sidewall height. Besides tire sizing, there are many safety-related markings on a tire’s sidewall that will be covered.

Reading Tire Size on the Sidewall

The size can always be found on both sides of the tire sidewall. Using the correct size for the vehicle is important for safety, fuel economy, and ride characteristics. Under most circumstances, the tire size should be the same for all four wheels. Tires should always be the same size on the same axle. The correct tire size for the vehicle can also be found on a tag on the inside door jam of the vehicle

For illustration purposes, the following tire size will be used to demonstrate tire type, size, speed, and load range. The tire size listed below is how it would appear on the sidewall of a tire.

P205/60R16 98S

  • P stands for a passenger rated tire, T would be temporary spare, and LT would indicate light truck.
  • 205 stands for the road surface width in millimeters
  • 60 indicates the aspect ratio for the sidewall height to the width. In this example, the sidewall height would be 123 millimeters (60% of 205)
  • R stands for radial
  • 16 indicates the wheel size or inside diameter of the tire in inches
  • 98 indicates the load index, LT load ranges would be an alpha designation like C D or E.
  • S indicates the speed rating

Calculating Tire Height and Diameter in Inches

To convert millimeters to inches simply multiply times .03937. In the above example size, the sidewall height in inches would be 4.84 inches (123 X .03937). To get the overall height or diameter of the tire double the sidewall height and add the wheel size. This method of calculation can be used for tire plus sizing to get the same height of the original tires.

4.84 + 4.84 + 16.00 = 25.68 or approximately 25 5/8 of an inch

Reading DOT Quality Codes on the Tire Sidewall

The U.S. Government developed a Uniformed Tire Quality Grading (UTQG) system that is printed on the sidewall. This grading system shows the uniformed tests of three safety categories. These safety scores can be found on the tire’s sidewall.

  • Treadwear
  • Traction
  • Temperature

Treadwear grade shows treadwear life. The grades are generally graded from 60 to 800, with 800 being the best.

Traction is based on the tire’s ability to stop in a straight line, on wet pavement with a locked wheel. Tire traction grades range from AA to C with AA being the best.

Temperature grade shows the tire’s ability to dissipate heat. Temperature grades range from A to C with A being the best.

There are also sidewall markings for mud and snow tires, usually marked with M & S. Snow tires that are rated for severe weather winter conditions have a special marking as illustrated in the following photo. Tire sidewall markings can help the car owner choose the right car or truck tire for their vehicle application.

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I am Derek Patrowsky, editor of AutoSportCatalog.com. I have over 17 years of experience in the automotive service industry and am part owner of a service facility in his hometown. Together with other writers, I hope this website will help you with your auto repair needs making better decisions when it comes to your vehicle.

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