A Tale of Two Tires

A case for radial tires on your classic car

by Ted Welch

As with most things that are not understood very well, myth and tall tales abound. This has always been true for tires in general, but even more so when it comes to the use of radial tires on older vehicles.

Generally speaking, vehicles produced before 1965 were fitted with bias-ply tire technology, which was at its zenith in the mid- to late 1960s. But change came swiftly.

First making their way into the automobile manufacturers' lines in 1965, radial tires quickly became the standard tire design. By 1973, all U.S. automobile manufacturers had standardized with the radial tire, mostly due to its fuel-economy benefits.

Since then, there has been a great deal of debate about the use of radial tires on vehicles not originally equipped with them. The key to unlocking the answers start with learning about the history and design of both the bias-ply and radial tire. From there we will try to separate the myths from the reality when exploring the tire options available to classic car owners.

BIAS-PLY HISTORY.

In 1898, the Goodyear Tire and Rubber Company (GT) discovered the process of vulcanizing rubber. To strengthen and mold the rubber, a number of layers or "plies" of fabric cords are embedded into it. Each layer is laid in an alternating diagonal pattern on the bias of the bead cord. The degree of the bias varied between manufactures, running between 30 degrees to 55 degrees to the bead cord.

For the next 60 years, bias-ply tires ruled the roads of America and gradually evolved from cotton cord belts in 1915, to rayon cord in the 1930s, and then to nylon cords in 1943. Improve technology was applied to bias-ply designs in 1954 with the advent of tubeless tires on Packards. The tire fast became the standard on all automobiles thereafter.

In 1959, steel-corded tires were introduced, followed by fiberglass-corded tires in 1963, still based on the bias-ply design. The level of bias-ply tire design has remained pretty much unchanged since around 1965 when radial tires started showing up in dealer showrooms.

The main advantage of bias-ply tires is in its load-carrying capabilities in relation to tire size. A smaller bias-ply tire can carry more load than a radial tire of similar size. A major drawback is higher friction, which creates higher tire temperatures and results in faster wear. Another problem: The tread contact area (the area were tread meets pavement) is smaller, and since the sidewall and tread area are constructed of one material, cornering affects the contact area more than on radial designed tires.

THE TREAD OF HISTORY.

Michelin first introduced steel-belted radial tires in Europe in 1948. Radial tires are so named because the ply cords radiate at a 90-degree angle from the bead cord, and the casing is strengthened by a belt of steel fabric that runs around the circumference of the tire. In radial tire design, the ply cords are made of nylon, rayon, or polyester.

In 1966, Michelin struck a deal with Sears to manufacture radial tires for sale under the Allstate label, and within four years Sears was selling one million units per year. In the mid-1960s, B.F. Goodrich embraced radial technology as a means to win market share from its larger rivals, and the company introduced the first American-made radial in the mid-1960s and supported the launch with its "Radial Age" advertising campaign of 1968.

The August, 1968, Consumer Reports awarded its top two spots to radials and documented the new technology's longer life, increased safety, handling, and economy relative to even top-of-the-line bias-ply tires.

The advantages of radial tires include longer tread life, better steering characteristics, and less rolling resistance, which increases gas mileage. On the other hand, radials have a harder riding quality, and technologically are more complex than bias-ply tires, so they cost more to produce.

MYTH AND FACT.