When you need an advice about your pride and joy of a vehicle, you usually ask your friends and peers. But you might not know there are government agencies as well that are made not only to advice you in the best way, but they also make policies and enforce them on different manufacturers regarding safety and well beings of the general consumers. One such agency in USA is National Highway Traffic Safety Administration (NHTSA).
NHTSA developed a grading standard for consumers to make informed decisions about their tire purchases. NHTSA came up with what is called Uniform Tire Quality Grading (UTQG). UTQG was made to provide consumers with useful information to help them purchase tires based on their relative treadwear, traction and temperature capabilities. The grades are assigned by the tire manufacturers based on their test results or those conducted by an independent testing company they have hired.
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. Tire makers use standardized Course Monitoring Tires (CMT) to test their newly developed tires (candidate tires) against. CMT tires are specially designed and built to American Society for Testing and Materials (ASTM) standard to have particularly narrow limits of variability. The vehicle repeatedly runs a prescribed 640 kilometers test loop for around 11600 kilometers. The vehicle can have its alignment set, air pressure checked and tires rotated every 1290 kilometers. The test tire’s and the CMT’s wear are measured during and at the conclusion of the test. The tire manufacturers then assign a treadwear grade based on the observed wear rates. CMT is assigned a grade and the test tire receives a grade indicating its relative treadwear.
A grade of 100 would indicate that the tire tread would last as long as the test tire, 200 would indicate the tread would last twice as long, 300 would indicate three times as long, etc. But, this test and treadwear grade is only there to inform the consumers about how the tire has ranked, and not imply how much a tire would last in the real world scenario.
Keep in mind that treadwear grade is a ratio and not a mileage. When you’re actually driving on the road, there are factors that aren’t exactly in your control like climate and road characteristics. How you drive your car and whether you take care of your vehicle tires (air pressure maintenance) is another factor determining how long your tires would last you. As a result, actual tire wear will vary considerably within the same tire line.
Different tire makers have different treadwear grades. You can compare one tire of same maker with another tire of the same company. But comparing treadwear grades of different tires of different makers will not help you as such.