Maybe you've heard of the Uniform Tire Quality Grade (UTQG) Standards and you want to learn more, or maybe you've noticed the words "Treadwear," "Traction," and "Temperature" on the sidewall of your tires, and you’re curious what they mean. Well, these often-misunderstood "grades" do provide some information for consumers, but unfortunately they're not as useful as originally intended when they were created by the Department of Transportation’s (DOT) National Highway Traffic Safety Administration (NHTSA).
It's important to note the DOT doesn't conduct the tests for UTQG grading. The tests are performed by the tire manufacturers (or a 3rd-party testing company) and reported to the DOT. So let's dive in to what each Grade tells us and how they are determined.
UTQG Treadwear grades are based on actual road use where the test tire is run in a convoy on a 400-mile test loop in Texas (West Texas, actually) for a total of 7,200 miles. The test vehicle can have its alignment set, air pressure checked, and tires rotated every 800 miles. At the end of the 7,200 mile test, the wear on the tires is measured and compared to a reference tire that was being run under the same conditions. If the test tire is expected to last as long as the reference tire, it receives a UTQG Treadwear grade of 100. If it is expected to last twice as long, it would receive a grade of 200. 300 means it is expected to last three times as long, and so on.
The reason the Treadwear grade may not be incredibly reliable is twofold. First, since the tires are only run for 7,200 miles, the tire manufacturers have to extrapolate the remainder of the data, and that can be open to some interpretation. Second, the tire manufacturers are allowed to under-report the Treadwear grade, just not over-report it. So if a tire technically may be able to achieve a 700 rating, the manufacturer (primarily the marketing department) might want to report it as 400 to make it "fit" better in a certain market segment. As a result, it is generally only somewhat helpful to compare Treadwear grades on tires from the same manufacturer, and we don’t recommend comparing grades between different brands.
The Traction grade, or traction rating, as they are commonly called, is based on the coefficient of friction of a locked (skidding) tire in a straight line on a wet surface. It doesn't evaluate any dry performance, cornering of any sort, or hydroplaning resistance.
The test tires are simply pulled on a "skid trailer" at 40mph over wet asphalt and concrete test surfaces. The brakes are momentarily locked, and sensors measure the coefficient of friction as the tire skids.
A tire that is on the verge of lockup but still rotating will generate a different coefficient of friction than the same tire if it is skidding. Since the vast majority of vehicles on the road today have anti-lock brakes, tire manufacturers design their products to work more effectively with these systems, as opposed to at full lockup. Because of this, the Traction rating isn't as real-world applicable today as it was when the test was designed. Even so, the traction coefficients and their corresponding grades are in the chart below:
| Traction Grades | Asphalt g-Force | Concrete g-Force |
|---|---|---|
| AA | Above 0.54 | 0.38 |
| A | Above 0.47 | 0.35 |
| B | Above 0.38 | 0.26 |
| C | Less Than 0.38 | 0.26 |
The UQTG Temperature grade, or temperature rating, is an indication of how heat is generated and/or dissipated by a tire. With better heat dissipation/tolerance, the tire is capable of higher speeds, and that is what is indicated by the Temperature grade. To determine the grade, an inflated tire is run against a high-speed test drum, and the grades and their corresponding speeds are below:
| Temperature Grades | Speeds in mph |
|---|---|
| A | Over 115 |
| B | Between 100 to 115 |
| C | Between 85 to 100 |
So, while UTQG grades (sometimes called UTQG ratings) do provide some information, unfortunately they're typically not as specific or applicable as consumers (or the test designers) would hope. It's also important to note that some tires (Light Truck tires, winter / snow tires, temporary spares, trailer tires, and others) are not required by law to display UTQG grades on the sidewall of the tires.
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