team for a tire to handle the power of the new Lancia Stratos and in the succeeding year, Pirelli introduced a wide tire with a reduced sidewall height like a slick, but with a radial construction for the Monte Carlo Rally winning works Stratos. Radial technology is now the standard design for essentially all automotive tires. Bias tires are still used on trailers due to their weight carrying ability and resistance to swaying when towed. For aircraft, the transition is happening more slowly, as tires are certified along with the airframe. A radial has less material in the sidewall, so it weighs less, runs cooler and lasts longer. For smaller planes, bias tires afford more stability at higher speeds and have stronger sidewalls. Construction A series of plies of cord reinforces a tire. Without this, a tire would be flexible and weak. The network of cords that gives the tire strength and shape is called the carcass. Since the 1960s, all common tires have a carcass of cords of polyester, steel, or other textile materials, inlaid with several layers of rubber. In the past, the fabric was built up on a flat steel drum, with the cords at angles of about +60 and −60 degrees from the direction of travel, so they criss-crossed over each other. They were called cross ply or bias ply tires. The plies were turned up around the steel wire beads and the combined tread/sidewall applied. The green (uncured) tire was loaded over a curing bladder and shaped into the mold. This shaping process caused the cords in the tire to assume an S-shape from bead to bead. The angle under the tread, the crown angle, stretched down to about 36 degrees. In the sidewall region the angle was 45 degrees, and in the bead it remained at 60 degrees. The low crown angle gave rigidity to support the tread and the high sidewall angle gave comfort. To increase strength, the manufacturer would increase the number of plies, and the heat buildup in the tire. By comparison, radial tires lay all of the cord plies at 90 degrees to the direction of travel (that is, across the tire from lip to lip). This design avoids having the plies rub against each other as the tire flexes, reducing the tire's rolling friction. This allows vehicles with radial tires to achieve better fuel economy than with bias-ply tires.