Over the same period that asthma rates have been rising, radials have virtually replaced bias plies as the standard tire for cars and trucks. A survey by Goodyear Tire and Rubber Co. found that 44 percent of auto tires sold in North America in 1976 were radials. By 1989, radials accounted for 94 percent of sales. Radials provide longer tread life and better fuel economy than bias-ply tires. But they also wear differently, Mr. Williams said.
Bias plies leave behind bits of rubber large enough to fall by the side of the road.
Studies show that radials create particles small enough to become airborne. This page has been accessed times.