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. The supposed hazards of using radial tires on vehicles that were originally Equipped with bias-ply tires are some of the hardest myths to dispel, partly because, as in most myths, some truths can be found. For instance, it's true that many older vehicles were not engineered to take advantage of radial tire designs. But that does not make using radial tires on older vehicles unsafe or a waste of money.
When combing through the myths to get to the facts, four areas emerge. Three deal with physical characteristics: tire size, contact area, and tire weight. The fourth deals with load-carrying capabilities, and is the concern of least importance. Let's address these areas by first placing them in context with myth.
MYTH: The suspension systems on older vehicles are not designed to use radial tires
This statement is true in the context that radial tires may not have been available to, or offered by, the manufacture at the time the vehicle was designed. The factors to look at when considering radial tire use on these cars in regard the problems that could be encountered are as follows:
Tire Weight: Radial tires, because of their steel-belt design are heavier than bias-ply tires of similar size. This additional weight may require heavier springs or modern gas shocks to help tame the additional weight. Unless you are looking to increase the sidewall height over that of the original size bias-ply tire, radial tire weight should not be a huge concern.
Contact Area: The larger contact area can make steering a chore on heavy vehicles that do not have power steering. The larger contact area may also make low speed cornering a bit more sluggish and less responsive. Proper selection and inflation can successfully overcome most of these issues.
Tire Size: A little research may be required to find a suitable size tire that can accommodate the vehicle's weight and still meet the OEM (Original Equipment Manufactures) size. As an example, locating 14" radial tires to accommodate a 5,000-pound vehicle could be a bit of a challenge today.
MYTH: You can't use tubeless radial tires on older tube rims.
If there is any truth to this claim, I have not seen it my restoration experience, and I have put tubeless tires on many a prewar rim without any notable problems.
But to make sure, I talked with an expert. Frank Mauro of Stockton Wheel Service, plainly states, "There were no changes to rim design in the late fifties when the tubeless tire came on the scene, in fact the idea was for backward compatibility to shift people with older cars to the new tubeless tires."
Frank also remarked that "If you find [that] you cannot use a tubeless radial on your stock rim, we can build one that looks stock and [will] work with any radial tire." Stockton Wheel Service has been in business since 1893 and is America's oldest wheelwright. They specialize in classic car and truck wheels and build custom wheels to suit the needs of just about anyone needing wheels and can be found online at stocktonwheel.com.
MYTH: The ride quality of bias-ply tires is better than radial tires.
As a general statement, this myth is just that -- myth. The ride quality of one design over the other is really in the materials used to build the tire rather than the design type itself. You can find poor ride characteristics in either design. Typically, radial tires do have a firmer overall ride than bias-ply tires, and in my opinion, that equates to a firmer ride over that of a squishy jello-like ride quality, which is not my idea of a controlled ride. But in this arena, you will have to be the judge.
One negative ride trait of bias-ply tires is what's called "standing set." This means vehicles equipped with bias-ply tires that stand still for long periods, without being driven, develop flat areas on the tread face. These areas pound like a cupped tire until they work themselves out during driving. This trait should give cause for classic car owners to take note of, since many classics are only driven on rare occasions.
On the other hand, choose a radial tire with an 80,000 miles treadwear life, and I will show you rolling rocks. The harder composition found in long treadwear rubbers used in some radial tires can produce a rather stiff or hard ride quality. Again, there are trade-offs here, too.
A hard compound, long-life radial will have a very firm ride, and it will steer better than soft compound radial tires found in 25,000 or 35,000 mile treadwear tires. However it is in these soft compound tires that you will find a better ride. Choosing a radial tire with a treadwear life of 40,000 miles is the best choice for having it both ways...but just a little.
MYTH: I have a restored vehicle and the radial tires look...well, wrong.
This might have been the case a few years ago, but many of the specialty tire manufacturers make everything from Redline Tires to Wide Whitewall Tires in the radial design. The real benefits here are that the tires are made for vehicles that were originally equipped with bias-ply tires. This means issues like weight, size, and contact area have been taken into consideration when developing these radial tires for today's market.
Will these reproduction radial tires get a pass from the show judges? I know people that change radial tires when they get to the show because of concerns about judging. So maybe not, but that type of judging is crazy anyway in my opinion. When I see radials in my judging, I think about how much the owner is enjoying his restoration, not why isn't the person torturing himself with bias-plies to make more brownie points.
Diamond Back Tires carry a full line of radial tires for classic and special interest cars and trucks. All their tires are made in the U.S. at their Conway, S.C. plant. You will not find any bias-plies in their inventory. They only do radial tires, which should be enough evidence to show that bias-plies are really a technology of the past.
RADIAL OR BIAS? I hope I've helped explain some of the facts and dispelled the myths of using radial tires on vehicles originally designed for bias-ply.
In the end it's up to you to decide, of course, which tire is best for your classic car. But I have no problem recommending radial tires because I know how much you will enjoy the drive. After all, that's why we restore classic cars, to enjoy them!