UTQG ratings explained: treadwear, traction, temperature

What the UTQG grades on a passenger tire mean, the AA to C and A to C scales, which tires are exempt, and why treadwear is a ratio, not a mileage.

Three grades sit on the sidewall of almost every passenger car tire sold in the U.S.: a treadwear number, a traction grade from AA down to C, and a temperature grade from A down to C. That trio is UTQG, the Uniform Tire Quality Grading the government requires under 49 CFR 575.104. The rule's own example reads "Treadwear 200 Traction AA Temperature A."

The UTQG chart

A grade is only as good as the test behind it. Each one is a single test, run one way, on purpose. That makes them comparable between tires. It doesn't make them a forecast for a customer's commute.

Where to find the grades

On the tire itself, the grades are molded into the sidewall between the tread shoulder and the widest point of the tire. Look there first. A new replacement tire also comes with a label stuck to the tread showing the treadwear number, with the traction and temperature letters circled from a printed row of AA, A, B, C and A, B, C, plus the federal explanation of each grade. Original equipment tires on a new car skip that tread label; the car maker has to list the possible grades in the owner's manual instead and point the owner to the sidewall.

NHTSA also keeps a tire ratings lookup on its website covering thousands of tire lines, most of the ones used on cars, minivans, SUVs and light pickups. It's the quickest way to check a tire you don't have in your hands.

Treadwear is a ratio, not miles

NHTSA's tire page puts it simply: "A control tire is assigned a grade of 100. Other tires are compared to the control tire." A 200 should wear twice as long as that control tire. The rule's own explanation uses 150, which "would wear one and one-half (1½) times as well on the government course as a tire graded 100."

The test explains why. Tires run in a convoy of two or four vehicles over the government course, alongside course monitoring tires, and the projected mileage is then corrected against those monitoring tires to account for environmental variations. Every grade is measured against the same yardstick. None of it is a promise about a customer's roads.

So the only honest arithmetic is a ratio. A 600 against a 300 is 600 ÷ 300 = 2, about twice the wear on the test course. Nothing in that sentence is miles. The rule adds the warning in plain words: real wear "may depart significantly from the norm due to variations in driving habits, service practices and differences in road characteristics and climate."

Customers will still ask how many miles a 500 gets. There's no federal answer to give them. Treadwear is a comparison, so sell it as one.

Traction: wet braking, straight ahead

Traction grades come from locking a wheel and skidding the tire on wet test surfaces of asphalt and concrete. To earn AA, a tire has to beat a traction coefficient of 0.54 on asphalt and 0.38 on concrete. The rule sets lower bars for the other grades.

The C row is an either/or: a tire at or under either number gets a C. The warning printed in the federal explanation is the part to repeat at the counter. The grade "is based on straight-ahead braking traction tests, and does not include acceleration, cornering, hydroplaning, or peak traction characteristics." A tire marked C, in the rule's words, "may have poor traction performance."

Temperature: what C really means

The temperature grade shows how well the tire resists building up heat, and gets rid of it, on an indoor test wheel. C is the floor. In the rule's words, it "corresponds to a level of performance which all passenger car tires must meet under the Federal Motor Safety Standard No. 109," and B and A mean better than that minimum. A tire graded C fails to finish the 500 rpm stage of the test; an A has to make it through the 575 rpm stage.

There's a catch built in. The grade assumes a tire that is "properly inflated and not overloaded." Too much speed, too little air or too much weight, alone or together, "can cause heat buildup and possible tire failure." A tire run low has left the conditions it was graded under.

How the grades are spread across tires today

NHTSA publishes how current tires break down. It's a useful check when a customer thinks a grade is rare.

Traction A covers most of the market. Among temperature grades, C is the smallest group at 4%. Traction C is rarer still: NHTSA counts only four tire lines.

Tires with no UTQG grade

The rule covers new passenger car tires. It does not apply to deep-tread winter-type snow tires, space-saver or temporary spares, tires with rims of 12 inches or less, or limited production tires, which the rule defines partly as no more than 15,000 a year of one design and size. A brand-new tire line also gets six months before the grades have to be molded on.

Light truck tires aren't on that list because they were never in scope: the section is written for passenger car tires. A customer comparing an LT tire by treadwear grade is comparing against a number that tire doesn't have to carry. Steer them to the load range and the load index instead.

UTQG on a used tire

The grades are molded into the rubber, so they stay on a used tire for its whole life. They describe how the tire was built, not how it has been treated. A 600 says how the tread wore on the test course when the tire was new. It says nothing about how much is left, so tread depth is still the number that sets the price. Record the grades if you like, and grade condition separately with the used tire grading checklist.