There are two distinct types of construction for tires--bias ply and radial ply. The construction method affects the durability, ride and fuel economy of the tires. Radial tires are the most common on cars and trucks.
The first use of pneumatic tires on an automobile was by the Michelin brothers, André and Édouard. in 1895. Their company became a leading producer of auto tires. For the first half of the 20th century, all tires produced for car and truck use were of bias-ply construction. Michelin invented and introduced the radial-ply tire in 1948; in the 1950s and 1960s, the use of radial car tires became widespread in Europe and Japan.
U.S. car and tire manufacturers resisted the change to radial tires until the 1970s. The imported cars coming to the U.S. had radial tires, and consumers began to demand the benefits of radial tires on their U.S.-built cars. By the early 1980s, all new cars were fitted with radial tires.
Tires have belts called plies that give a tire its shape. Plies are layers of polyester, fiberglass or steel cords embedded in the rubber of a tire. A bias-ply tire has the layered belts running at angles to each other and to the body of the tire. Ply numbers 14 and 16 in the diagram are bias plies.
Radial-ply tires have the belts at a 90-degree angle to the tire, and the belts overlap rather than cross each other. The ply labeled 12 in the diagram is a radial-ply. Radial tires have another belt, usually of steel cord, running around the tire under the tread. Radial construction allows the sidewall of the tire to flex under loads without affecting the contact of the tread with the road.
Radial tires have significant performance advantages over bias tires. Radial tires result in lower fuel consumption and have longer tread life. They have a larger contact patch or footprint on the road, providing better traction and handling. Radial tires cost more than comparable bias-ply tires, but the extended tire life and fuel savings makes using radials the more cost-effective choice.
Tires used in heavy construction and on agricultural machinery are still mostly bias construction. However, radials are making inroads in these areas.
Classic car owners often want bias tires to keep their cars original. Tire manufacturers exist that produce classic bias tires using the original molds.
Tires made especially for small and medium trailers are bias construction. Bias tires provide good load capacity compared to tire weight, and trailer tires are not expected to provide good handling or fuel economy.
