Road-testing the accuracy of tire tread-wear ratings

Nov 13, 2005

By the editors of Consumer Reports

Until now, you had to trust the tread-wear ratings on the sidewalls and a tire's tread-wear warranty to tell you how long your tires would last. Consumer Reports' new tests show that claims don't always meet reality.

Some tire makers, CR found, overestimate tread wear. Others underestimate it. And warranties are prorated: You get only partial credit toward a new tire based on the difference between the mileage on your worn-out tire and the warranty's mileage threshold. (Tread is considered worn out when it reaches the industry norm of 2/32-inch deep.) Most warranties don't cover damage resulting from potholes or other road hazards.

The magazine recently included results of its own tread-wear tests in ratings of all-season tires — the kind that are standard on most new cars and light trucks, and that accounted for 83 percent of the replacement market last year. In addition to CR's usual tests measuring handling, braking, and ride comfort under a variety of conditions, the magazine commissioned accelerated wear tests that closely followed the same procedures specified by the government for manufacturers.

For the all-season tires tested, manufacturers' tread-wear ratings (the Uniform Tire Quality Grades found on a tire's sidewall) range from 520 to 740. Theoretically, a tire with a UTQG grade of 800 should last twice as long as one rated 400. Some scores from the tests followed the tire makers' claims fairly closely. For example, four models that had modest tread-wear grades (520 to 560) and warranties (65,000 to 75,000 miles) scored fair in CR's wear-test ratings. Likewise, a tire with a 700 UTQG grade and an 80,000-mile warranty had excellent tread wear in the tests.

But others didn't come close. One would expect a model that claims a high 700 grade and 80,000-mile warranty to provide at least "very good" tread life. The Kelly Navigator Platinum TE, however, could manage only "fair." Conversely, the Daytona Grenadier PLE has a more modest 640 grade and an 80,000-mile warranty, yet has excellent wear rating based on the tests.

The magazine's editors say they believe CR's tread-wear ratings are the best indicator of true tire-wear potential. The manufacturer's warranty is your second-best option, as a failure to meet this claim could mean that the tire maker must reimburse you some of the tire's price. Use the manufacturer's UTQG tread-wear grades as a loose guideline.

In the tests, two Michelin all-season models emerged as best for all weather conditions. (Prices are per tire for size P205/65R15, where "15" denotes the wheel diameter in inches. You can expect similar performance for 14- through 17-inch sizes of the same models.) The Michelin X Radial ($111, sold only to members of shopping clubs), is a very good all-around performer. The Michelin HydroEdge ($100) performs capably, but is noisier than its brandmate.

If driving on icy roads isn't a factor, consider the top-rated Goodyear Assurance TripleTred ($80), the Hankook Mileage Plus II H725 ($50), and the Yokohama Avid TRZ ($70). These tires do everything well, except braking on ice.

And if long tread life is important to you, CR recommends four models: the Michelin HydroEdge and Yokohama Avid TRZ noted above, plus the Dayton Grenadier PLE ($48) and the Bridgestone Turanza LS-T ($78). The Dayton and Bridgestone trail the others in overall performance. Of those four, only the Michelin HydroEdge scored better than "fair" for braking on ice, and the Bridgestone lagged in snow traction.

Consumer Reports recommends discarding your tires before they get to the 2/32-inch mark.