Certain Michelin tires lasted longest in a test.

The test was conducted by the National Highway Traffic Safety Administration, an arm of the Transportation Department. Testing showed that, among 134 radial tires from 18 companies, Michelin did best with its XH, which has a tread wear rating of 330, or 66,000 miles under average driving conditions. A tire with a tread wear rating of 100 should get 20,000 miles, while one with a rating of 250 is expected to last 50,000 miles. The ratings also showed all tire companies had good and poor mileage performers--including Michelin’s XWX at a 100 rating or 20,000 miles.