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Barry's Tire Tech


B arry's T ire T ech

   This is a series of articles on the technical aspects of tires, their care, and usage. My primary purpose is to reduce the risks that we all face every day, and since tires is just about the only thing I know about..........

   Please drop me a note if you have a topic you want to see:



By Barry Smith
Tire Technical Consultant

Uniform Tire Quality Grading is a US government mandated tire rating system. It is required for all Passenger type tires, except those used in a light truck application, and those classified as "mud and snow" tires.

The exception for light truck application means that tires P235/75R15 Standard Load and smaller are required to have a UTQG rating and tires P235/75R15 Extra Load and larger, are not. Many P metric tires used on Sport Utility Vehicles are larger than the requirement and, therefore, may not carry a rating.

Tires used in other applications are also not covered by UTQG ratings. LT metrics, tires frequently used on large pickup trucks and vans, and tires used on trailers that carry an ST in the size, would not have a rating.

The UTQG rating consists of three ratings: Treadwear, Traction, and Temperature.

The Treadwear rating is a number based on a vehicle test where tires are compared to a control tire. The rating is based on a percentage in projected wear life. So a tire rated at 400, projected twice as far as a tire rated at 200. Since there are many factors that influence wear, such as vehicle speed, road surface, climate, vehicle alignment, and driving habits, these ratings are merely an indication of the wear characteristics of the tire.

The Traction rating is a letter based on a straight-line wet surface braking test. The ratings are AA, A, B, and C. AA is the highest rating possible. The AA rating is relatively new and many tires currently rated as A might qualify for an AA rating, but have not yet been tested. It is important to remember that the test does not test hydroplaning resistance, nor dry or snow traction nor, cornering capability - wet, dry or snow.

The Temperature rating is a letter based on a step speed test. The possible ratings are A, B, and C. The rating is a bit of a misnomer. While temperature does play a role in the speed capability of a tire, it is not the only factor.

It is important to note that these ratings are based on standardized testing conditions. The tests do not reflect tires operated overloaded, underinflated, and/or misaligned. It should also be noted that one tire might be a low "A" and another a high "B", so the actual performance differences might be small.

It is not uncommon for there to be differences in UTQG ratings within a given tire design. Sometimes a vehicle manufacturer will require certain properties for the tires supplied to their vehicles, which can affect the ratings, both positively and negatively. Sometimes there are differences between small sizes and large sizes in a given design. These things can affect the actual rating put on the sidewall.

One little quirk: Testing tires for treadwear can be an expensive proposition. So the government merely asks the tire manufacturers to be able to justify their rating. In my experience this seems to mean different things to different people and a wide range of "justifications" are being used.

Another little quirk: Each tire manufacturer has its own philosophy about UTQG ratings, especially when it comes to the treadwear rating. Some view the rating as a huge marketing tool, while others tend to think of it as an implied warranty. Be cautious when you compare ratings - they may not be "apples to apples".

© 2003 Barry Smith

Additional Information provided courtesy of
ALLDATAdiy.com and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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