UTQG
UTQG stands for Uniform Tire Quality Grading.
The National Highway Traffic Safety Administration (NHTSA) established the Uniform Tire Quality Grading Standards (UTQGS) in 49 CFR 575.104[citation needed].
Dedicated winter tires, also known as snow tires, are not required to have a UTQG rating
Components
The UTQG rating is made up of three components:
Treadwear
The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test track. A tire graded 200 would last twice as long on the government test course under specified test conditions as one graded 100. These treadwear grades are no guarantee of actual tire mileage; differences in driving habits, service practices, climate, and road characteristics will affect a tire's longevity.
Traction
Traction grades, from highest to lowest, are AA, A, B and C. They represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. The testing does not take into account cornering, hydroplaning or acceleration.
The UTQGS traction test procedure measures a tire’s coefficient of friction when it is tested on wet asphalt and concrete surfaces. The test tire is installed on an instrumented axle of a traction trailer, which is towed by a truck at 40 miles per hour (mph) over wet asphalt and concrete surfaces. The tow truck is equipped with an on-board water supply system that sprays water in front of the test tire. The brakes, from the test tire only, are momentarily locked, and sensors on the axle measure the longitudinal and vertical forces as it slides in a straight line. The coefficient of friction for the pair, test tire and surface, is then determined as the ratio of the longitudinal and vertical forces.
The UTQGS traction rating procedure specifies that the traction coefficients for asphalt and for concrete are to be calculated using the locked-wheel traction coefficient on the tire, or sliding coefficient of friction. More specifically, upon application of the brakes, the tire is subjected to shear between the wheel and the road surface, and deforms towards the rear of the vehicle. This generates a traction force to oppose the motion of the vehicle. As braking torque increases, the tire deforms more and tread elements near the rear of the contact patch with the road begin to slip rather than grip. The coefficient of friction rapidly reaches a maximum value at about 10-20 percent slip, and then declines as the longitudinal slip values increase to 100 percent, which represents a fully locked tire. The maximum coefficient of friction in the 0-100 percent slip range is termed “peak” coefficient of friction, and the lower coefficient value for the fully locked tire is termed “slide” coefficient of friction. [1]
| Grade | 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 |
Temperature
The temperature grades, from highest to lowest, are A, B and C. These represent the tire's resistance to the generation of heat at speed. Tires graded A effectively dissipate heat up to a maximum speed that is greater than 115 mph. B rates at a maximum between 100 mph and 115 mph. C rates at a maximum of between 85 mph to 100 mph. Tires that cannot grade up to C or higher cannot be sold in the US. [2]
References
- sidewall markings explained by the NHTSA
- SaferCar.gov - U.S. Government service to look up treadwear grades on different type of tires.
