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Demystifying The Tire Sidewall Code

American Government Special Collections Reference Desk

Demystifying The Tire Sidewall Code

Debbie Pettitt
Amazines.com
December 14, 2005

So, you need new tires for your car or truck, but how do you know what to buy? What do all those alphanumeric codes printed on the tire sidewalls mean, anyway? If you're in the market for new tires, you may simply want to replace your worn tires with exactly the same tire it came with. But you MAY want to consider an upgrade. If you know how to read the tire sidewalls, chock full of valuable information, you've got an advantage over most people and are prepared to make an informed decision. So let's get underway!

Tire Size Markings (example: P215/65R15 89H)

Broken down: P = Passenger Other designations are LT = Light Truck T = Temporary (spare tire)

215 is the width (in millimeters) of the tire from sidewall to sidewall. A wider tire has more grip but the bad news is that you lose fuel economy, hear more noise and the tires don't work as well in the rain.

65 is the aspect ratio The aspect ratio is the ratio of sidewall height to tire width. With regards to aspect ratio, the larger the number, the taller the tire sidewall. Tall (60-75) is great for a quiet ride but causes howling in turns. Short (35-55) is better for handling--more for sports cars.

R indicates Radial. This means it is constructed with a series of support belts sideways under the tread. Other designations include B for Belted Bias and D for Diagonal Bias The standard, and what you'll see most often, is R.

15 is the wheel (or rim) diameter, in inches.

89 is the load index H is the speed rating Speed ratings indicate the top speed under ideal conditions. Higher-rated tires are usually made of softer rubber and will have shorter UTQG tread life. Here are a few of the more common speed ratings: R= 106, S=112, T=118, U=124, H=130, V=149, W=168, Y=186. Along with this speed rating, you have a load index which indicates the approximate weight the tire can carry. Some of the more common load weights are as follows: 85 = 1,135 pounds, 86 = 1,168 pounds, 87 = 1,201 pounds, 88 = 1,235 pounds.

UTQG Ratings

Passenger car tires are accompanied by a UTQG Rating (Uniform Tire Quality Grading, mandated by the Federal Government) which rates the tread life of tires by looking at tread wear, traction and temperature resistance. The UTQG Rating is usually found opposite the tire size markings and will be in three separate ratings: treadwear, traction and temperature.

The treadware grade standard is 100. A grade of 200 means the tread would wear twice as well as a tire graded 100.

Traction grades run from AA to C, with AA being the highest grade and C meaning the tire brakes poorly on both wet concrete and wet asphalt.

Temperature grades rate the tire's resistance to and ability to dispel heat. Those grades are A (resists heat well), B (not as good as A) and C (passes minimum safety standards.) Keep in mind that heavy loads, under-inflation of the tires, and high speeds can all affect the tire temperature.

You should note that these tire grades rate tires measured under controlled conditions. Factors such as driving habits, road conditions, climate, etc., are not considerations and may affect the actual performance of your tire.

DOT

DOT (Department of Transportation) indicates the tire is in compliance with applicable DOT safety standards. Next to DOT is an identification or serial number--codes that designate where and when the tire was produced.

You'll also find other information on the sidewall such as the type and composition of the tire, the maximum cold inflation (PSI) and maximum load in pounds.

So as you can see, tires carry a huge amount of information. But it's really not all that complicated once you learn to read the code.

Debbie Pettitt is webmaster for Everything Tires, your tire resource. For more information on tires, visit http://everythingtires.com



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