About Tires

Tires are more than just black and round. Much more. They utilize an innovative mix of chemistry, physics and engineering. And we're here to help explain. Learn how to read your sidewall, understand tire construction and speed ratings, and find the right tires for your car.

Reading A Tire Sidewall

  • Tire Type
  • Tire Width
  • Aspect Ratio
  • Construction
  • Wheel Diameter
  • Load Index
  • Speed Rating

Tire Type

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.

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, which uses the metric system.

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.

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.

Wheel Diameter

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

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.

Speed Rating

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.

A tire's sidewall is simply 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.

michelin tires transportation safety code

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.

michelin uniform tire quality grading code

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 tire meets the Rubber Manufacturers Association's standards for a mud and snow tire. The letters can be found in the following combinations: M+S, M/S, and M&S. All-season tires carry this mark.


Tire Construction

The typical radial tire consists of six main parts. Hover your mouse over the features to the right to learn more.

Inner Liner

The days of tubed tires are over. Today's modern tires utilize synthetic rubber instead-specifically butyl rubber*-which is virtually impenetrable to water and air. However, over time, there will be slight air loss, so check your pressure every month.

Carcass Ply

The carcass ply is the layer above the inner liner and consists of thin textile fiber cords (or cables) bonded into the rubber. These cables are largely responsible for determining the strength of the tire.

Beads

The beads clamp firmly against the tire's rim to ensure an airtight fit and keep the tire properly seated on the rim.

Sidewall

The sidewall protects the side of the tire from impacts with curbs and the road. This is where the important details about the tire can be found, such as tire width and speed rating.

Crown Plies (or belts)

Crown plies provide the rigid base for the tread.

Tread

The tread provides traction and cornering grip for the tire and is designed to resist wear, abrasion and heat.