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
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:
This describes the fundamental characteristics of your tire. Size, construction,
speed rating and more.
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.
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.
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
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.
This number (in inches) indicates that the
tire is designed to fit on a wheel with a 18-inch diameter.
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. to a tire with 100.
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
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.
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
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 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.
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
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.
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