To the casual observer all tires look the same. But if you look
carefully, you'll find modern tire construction offers a degree of
handling, ride comfort, traction, treadwear and fuel economy that
far exceeds tires built just a few years ago.
Today there are tire designs that contain up to 200 raw materials as well
as a complex architecture of steel belts, textile plies and computer
designed tread patterns. Tire manufacturers strive to deliver the most
competitive designs in terms of performance and wear.
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 treadwear 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.
Groves are built into tread designs for channeling away water. Shoulder designs
provide protection as well as additional traction during hard cornering.
