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Reading a Tire Sidewall

A tire’s sidewall is pretty much what it sounds like – the outer and inner “walls” on the sides of a tire, if facing a tire on its side. Every sidewall has its own unique information that is divided into three main sections:

1. TIRE SPECS

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

Tire Type

This designates the type of vhicle 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.

Aspect Ratio

This identifies the tire's aspect ratio, which is the relationship of the tire's sidewall height to the tire's width. In this example, the sidewall height of the tire is 55% of its width. The lower the ratio, the smaller the sidewall height, which means better cornering, but a rougher ride.

Wheel Diameter

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

Speed Rating

This indicated 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.

Tire Width

Also called Section Width, 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, whic uses the metric system.

Construction

This is the tire's internal construction, which is "radial". Almost every tire on the road has radial construction, which means the cords of the carcass plies inside the tire "radiate" directly across from one side of the tire to the other. Other letters used are D, for diagonal construction, and B, for belted.

Load Index

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. (To see the load index chart on the Tire Speed Ratings & Tread Life page, click here.)

2. DEPARTMENT OF TRANSPORTATION SAFETY CODE

This assures that your tire complies with all Department of Transportation (DOT) and Transport Canada 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.

DOT

Department of Transportation

YR

Identify the size of the tire

50

Identify the tire manufacturing week

B9

Identify the factory where the tire was manufactured

UJNX

Identify optional characters by the manufacturer to describe the characteristics of the tire

08

Identify year of tire manufacture

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, a Mountain Snowflake symbol tells you that the tire meets or exceeds industry-established snow traction performance requirements.