During our last visit, I shared the history and evolution of the regular passenger car tire into the sophisticated device that it is today. I want to take this conversation a bit farther and discuss another aspect that affects tire performance, the tire tread.
The tread is the design or pattern on the face of the tire that comes in contact with the road surface. The function of the tread is to increase the durability and operational life of the tire. It is the pattern of the tread combined with specially formulated rubber compounds that gives each tire its specific performance characteristics.
The word tread is often used casually to refer to the pattern of grooves molded into the rubber. Those grooves are correctly called the tread pattern. The grooves are not the tread. The grooves in the rubber are designed to allow water to be expelled from beneath the tire and prevent hydroplaning. The proportion of rubber to air space on the road surface directly affects its traction.
Design of tire tread has an effect upon noise generated, especially at freeway speeds. Generally there is a tradeoff of tread friction capability; deeper patterns often enhance safety, but simpler designs are less costly to produce and actually may afford some roadway noise mitigation. Tires intended for dry weather use will be designed with minimal pattern to increase the contact patch.
Street tires will also include wear limit indicators in the form of small raised bridges within the grooves. When the tread is worn down enough that the limit indicators make contact with the road, the tire is deemed to be at the end of its service life.
The following tread designs are examples of basic types used throughout the tire industry:
Rib-Block Type – This pattern combines block-type tread in the center with a shoulder rib design with the following advantages: low rolling resistance, comfortable ride, relatively low noise generation, and good traction on snow or in muddy terrain;
Lug Type – In this pattern, the grooves are cut across the tread with the following advantages: high braking force and excellent traction on unpaved surfaces;
Block Type – With this tread pattern the grooves are cut across the tread and has the following advantages: outstanding braking force and traction, with good traction on snow or in muddy terrain;
Rib Type – This pattern features tread and grooves that follow the circumference of the tire and have the following advantages: low rolling resistance, comfortable ride, good steering, and relatively low noise generation;
Combined Block-Lug Type – This pattern combines a rib-type in the center with a lug-type design and has the following advantages: good steering stability and less side slippage than the rib tread, excellent traction and braking force, and is well suited for paved and unpaved surfaces.