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Archive for Wednesday, October 19, 2005

Tread ratings can be misleading

October 19, 2005

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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. Our new tests show that claims don't always meet reality.

Some tire makers, we found, vastly 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, moreover, don't cover damage resulting from potholes or other road hazards.

We recently included results of our 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 our usual tests measuring handling, braking, and ride comfort under a variety of conditions, we commissioned accelerated-wear tests that closely followed the same procedures specified by the government for manufacturers.

For the all-season tires we 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 our tests closely 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 our wear-test ratings. Likewise, a tire with a 700 UTQG grade and an 80,000-mile warranty had excellent tread wear in our 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 our tests.

We believe our 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 your third option, but only as a loose guideline.

In our 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. (We test that on a skating rink near our Connecticut track.)

And if long tread life is important to you, we recommend 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.

Although tire tread may be "legal" down to 2/32 of an inch, we think you should discard them well before then: Our tests have shown that tires typically lose much of their wet-weather and snow grip long before they rea

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