Radial tire structure
To the casual observer all tires look the same. But if you look carefully, you will 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 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
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.