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In 1946 the tire industry was revolutionized by the introduction of the radial tire. A cross section of the
radial design is shown above. Today, virtually all tires sold are radials due to their benefits of superior
handling, ride quality and wear.
The benefits of radial construction are attributed to the design of the tire's casing - the part of the tire
underneath the tread that forms the foundation of the tire. The casing is made up of a series of cords (most
typically polyester) which are combined to form layers or plies. In a radial tire, these plies are positioned so
the cords run alongside each other in a series of circular bands across the tread of the tire. Radial construction
allows the tire to better flex and absorb the irregularities of the road surface. The radial design also produces
much less friction resulting in much longer tread life.
The top layer of the radial casing usually consists of steel belts made up of woven strands of steel cord. Steel
belts provide a stable foundation for better tread wear and traction, and also protect the casing against impacts
and punctures. Other components may include bead chaffers and cap plies - usually built into performance tires to
enhance cornering and stability at high speeds.
The outermost part of the tire, the tread, usually attracts the most attention. The material used is referred to as
tread compound, which varies from one tire design to the next. A winter tire, for example, has a compound that
provides maximum traction in cold weather. Competition tires, at the other extreme, use a compound designed for
very high temperature ranges. The great majority of tires are built with an all season compound that delivers
traction in the broad middle range of every day driving conditions. In addition, this compound must deliver good
wear; this dual goal of traction and wear remains one of the most challenging design parameters for tire
manufacturers.
While tread designs vary tremendously, the elements of the tread are consistent in their use. The tread block
provides traction at its leading and trailing edge. Within the block, sipes are often molded or cut to provide
additional traction. Grooves are built into tread designs for channeling away water. Shoulder designs provide
protection as well as additional traction during hard cornering. |