Tires possess impressive technology beneath the tread. The untrained eye may look at a tire and see rubber sidewalls, a bunch of numbers and letters, and a tread pattern. While the outside visible aspects of the tire are very important in terms of the overall tire construction and performance, the inner workings of the tire - the rubber, plies and materials beneath the tread - are just as important. These elements below the surface are responsible for the way a tire wears and performs, offering stability and longevity.
Regardless of tire technology advancements, tire design still incorporates the original pneumatic design that was developed and fitted on an automobile by the Michelin brothers. This design is known as bias tires. The terms bias tires, belted bias, and radial tires are quite commonplace within a tire shop. These are all terms that refer to the construction of the tire beneath the surface and outer layer of the sidewall. Bias tires have distinct advantages and disadvantages and are still constructed for very specific uses on certain vehicles, most of which are not passenger automobiles.
What are Bias Tires?
Bias tires are distinguished by the construction of their inner plies. A tire ply is a layer inside the tire that can be constructed of various materials including rubber, steel, nylon, and fiberglass. The plies may also consist of a combination of these materials. After one layer is laid, another layer, or ply, is added. Multiple plies offer a tire versatility and durability, and these plies change based on the tire's intended usage.
Bias tires are unique because they possess plies which run diagonally across the width of a tire. These diagonal plies crisscross beneath the tread and sidewall, running from bead to bead. Generally, these plies are run between 30 and 40 degree angles. The benefit of bias tires is in their ability to tackle rough roads without sacrificing ride comfort. However, these tires also have some negatives. The rolling resistance of biased tires, for example, is diminished due to the angled ply construction.
When bias tires were developed, ride comfort was much more of a concern than rolling resistance. People generally only drove short distances. In addition, fuel was cheap at the time, and concern for the environment was not widespread. Many years later, the development and perfection of radial tires would surpass the performance capability of bias tires; however, bias tires are still manufactured and used on many tractors and other heavy machinery.
To compete with radial tire performance, belted bias tires were developed, which incorporate reinforced steel, nylon, or fiberglass cords that run across the bias plies. This decreases the rolling resistance of bias tires without sacrificing the smooth ride that one would expect from biased tires.
Specialty Bias Tires for Classic Cars
Many owners of classic cars, hoping to use original parts, will only put bias tires on their vehicles. There are specialty manufacturers which offer bias tires to fit a variety of classic vehicles, allowing these cars and trucks to maintain their historical integrity.