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Reading Your Sidewall

January 14th, 2014

1. Tire Specs

This describes the fundamental characteristics of your tire. Size, construction, speed rating and more.

Tire Class - "P"

This designates the type of vehicle the tire fits. P is for passenger metric. Other letters are LT (for light truck), T (for temporary spare) and ST (for special trailers). If your tire has no letter, it signifies that your tire is a euro “metric” size.

Section Width - "225"

This is the width of the tire (or thickness) in millimeters, if measured from a tire’s widest point of its outer sidewall to the widest point of its inner sidewall. Why millimeters? It originated in Europe, which uses the metric system.

Aspect Ratio - "55"

This number (in inches) indicates that the tire is designed to fit on a wheel with a 18-inch diameter.

Tire Construction - "R"

This number (in inches) indicates that the tire is designed to fit on a wheel with a 18-inch diameter.

Wheel Diameter - "18"

This number (in inches) indicates that the tire is designed to fit on a wheel with a 18-inch diameter.

Load Index - "97"

This indicates how much weight the tire is certified to carry at maximum safe inflation. It doesn’t mean 97 pounds, because it’s actually an assigned value that corresponds with its “actual” load capacity found on a load index chart. If you look up 97 on the chart, you’ll find 1,609 pounds.

Speed Rating - "T"

This indicates the maximum safe speed at which a tire is certified to carry a load under specified conditions. Speed ratings range from A (lowest) to Y (highest), with one exception: H falls between U and V. To find the maximum speed for your tire, refer to the speed rating chart*. Exceeding the lawful speed limit is neither recommended nor endorsed.

2. Department of Transportation Safety Code

This assures that your tire complies with all Department of Transportation (DOT) safety standards. After the DOT insignia is your tire’s identification number, which begins with the tire’s manufacturer and plant code where the tire was manufactured (two numbers or letters). The ninth and tenth characters tell the week the tire was manufactured. The final number(s) signifies the year the tire was manufactured.

3. UTQG Code

The Uniform Tire Quality Grading (UTQG) was established by the National Highway Traffic Safety Administration (NHTSA) to test tires following government prescribed test methods and then grade each tire on three main components:

  • Treadwear: This is the wear rate of the tire, comparable only to other tires within a tire manufacturer’s line. 100 is the baseline grade. Therefore a tire with 200 would theoretically last twice as long on the government’s course compared to a tire with 100.
  • Traction: Traction grades are AA, A, B and C (with AA being the highest grade). They represent the tire’s ability to stop straight on wet pavement as measure on a specified government track. Any tire rated under C is considered unacceptable for road travel.
  • Temperature: The temperature grades, from highest to lowest, are A, B and C. These represent the tire’s ability to dissipate heat under controlled indoor test conditions. Any tire rated below C is considered unacceptable.

4. Icons

Some tires have unique benefits, as showcased with specific icons. For example, the MICHELIN® Green X® Marking is a guarantee that the tire provides a level of energy efficiency among the highest in the market for its category without compromising traction and treadwear. The letters M and S (M +S) indicate that the tiremeets the Rubber Manufacturers Association’sstandards for a mud and snow tire. The letterscan be found in the following combinations:M+S, M/S, and M&S. All-season tirescarry this mark.

  Posted in: Tires 101