Tire Markings 101

christiancarguy — Sat, 19 Dec 2009 05:26:38 +0000

The Markings on the Tire are puzzling. Here are the pieces.

Sidewall Outer Circle

P as in P215/65 R 16 89H M+S
The “P” indicates the tire is for passenger vehicles.

LT = light truck

HT = Heavy truck

ST = Special Trailer tire

TT = Tractor tire

Nominal Width (215)
This three-digit number gives the width in millimeters of the tire from sidewall edge to sidewall edge. In general, the larger the number, the wider the tire.

Aspect Ratio

(65)
This two-digit number, known as the aspect ratio, gives the tire’s ratio of height to width. Numbers of 70 or lower indicate a short sidewall for improved steering response and better overall handling on dry pavement.

R ®
The “R” stands for radial. Radial ply construction of tires has been the industry standard for the past 20 years.

Rim diameter code (15)
This two-digit number is the wheel or rim diameter in inches. If you change your wheel size, you will have to purchase new tires to match the new wheel diameter

Load index (89)
This two- or three-digit number is the tire’s load index. It is a measurement of how much weight each tire can support. You may find this information in your owner’s manual. If not, contact a local tire dealer. Note: You may not find this information on all tires because it is not required by law.

Severe snow conditions
The “M+S” or “M/S” indicates that the tire has some mud and snow capability. Most radial tires have these markings; hence, they have some mud and snow capability.

Speed Rating

“Note” If your tires aren’t speed rated you should never exceed 99MPH
The speed rating denotes the speed at which a tire is designed to be driven for extended periods of time. The ratings range from 99 miles per hour (mph) to 186 mph. These ratings are listed below.

Note: You may not find this information on all tires because it is not required by law.

Q	99 mph	H	130 mph
R	106 mph	V	149 mph
S	112 mph	W	168 mph*
T	118 mph	Y	186 mph*
U	124 mph

*For tires with a maximum speed capability over 149 mph, tire manufacturers sometimes use the letters ZR. For those with a maximum speed capability over 186 mph, tire manufacturers always use the letters ZR.

Traction grades are an indication of a tire’s ability to stop on wet pavement. A higher graded tire should allow a car to stop on wet roads in a shorter distance than a tire with a lower grade. Traction is graded from highest to lowest as “AA”, “A”, “B”, and “C”.

Of current tires:

3% are rated “AA”

75% are rated “A”

22% are rated “B”

only 1 line of tires rated “C”

Temperature grades are an indication of a tire’s resistance to heat. Sustained high temperature (for example, driving long distances in hot weather), can cause a tire to deteriorate, leading to blowouts and tread separation. From highest to lowest, a tire’s resistance to heat is graded as “A”, “B”, or “C”

Of current tires:

27% are rated “A”
59% are rated “B”
11% are rated “C”

Treadwear grades are an indication of a tire’s relative wear rate. The higher the treadwear number is, the longer it should take for the tread to wear down.

A control tire is assigned a grade of 100. Other tires are compared to the control tire. For example, a tire grade of 200 should wear twice as long as the control tire.

Of current tires:

15% are rated below 200

25% are rated 201 – 300

32% are rated 301 – 400

20% are rated 401 – 500

6% are rated 501 – 600

2% are rated above 600

Passenger Vehicle – Sidewall Inner Circle

U.S. DOT Tire Identification Number
This begins with the letters “DOT” and indicates that the tire meets all federal standards. The next two numbers or letters are the plant code where it was manufactured, and the last four numbers represent the week and year the tire was built. For example, the numbers 3197 means the 31st week of 1997.

The other numbers are marketing codes used at the manufacturer’s discretion. This information is used to contact consumers if a tire defect requires a recall.

Tire Ply Composition and Materials Used
The number of plies indicates the number of layers of rubber-coated fabric in the tire. In general, the greater the number of plies, the more weight a tire can support. Tire manufacturers also must indicate the materials in the tire, which include steel, nylon, polyester, and others.

Maximum Load Rating
This number indicates the maximum load in kilograms and pounds that can be carried by the tire.

Maximum Permissible Inflation Pressure
This number is the greatest amount of air pressure that should ever be put in the tire under normal driving conditions. For more info visit Safecar.gov

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Tire Markings 101