Bias Ply vs. Radial Tires: What’s Right for Your Car?
Depending on the year and intended use of your project car, you may consider the advantages and disadvantages of radial and bias ply tires. The bias ply vs radial debate typically comes into play for vehicles built before the 1975 model year, as this was a crucial turning point in American car manufacturing. Before, radial tires were a seldom-seen option on new cars and trucks, but many American car manufacturers switched to radials for better fuel economy. There were still folks who continued using bias ply tires well into the 1980s, but they would ultimately be phased out, except for certain commercial tires, agricultural tires, racing tires, and other specialty applications. Radial tires truly changed how vehicles handled on the highway, and they provided less rolling resistance, resulting in better fuel economy, improved tread wear, and better overall performance.
Despite all the advantages that radial tires provide, there are still plenty of reasons to use a bias ply tire, and we’ll take a deep dive into those reasons and all the differences you may experience between the two vastly different tire designs.
For hot rods and custom cars, tire and wheel selection revolve around style and stance, and that can strictly be a matter of preference, but for pure restorations, it’s about bringing a car back to its original condition. A generic radial tire from the local department store doesn’t accomplish any of those goals, so enthusiasts often seek out specialty tires to provide authentic fitment and style. And while they cost more than the generic radials at the department store, the advantage is the period-correct appearance.
If you’re going for authenticity, then it’s essential to know what your car had from the factory or what it would’ve had during the era that you’re replicating. Hot rodders were slower to change over to radials, many using bias ply tires well into the 1980s. Then, of course, if you get into Pro Street cars, T-Buckets, drag cars, or anything racing-related, most of those remain bias-ply construction to this day, but let’s get into the design differences and handling differences you can expect between the tire construction types.
What are the Various Types of Tire Construction?
Bias-ply tire construction dates back to the 1900s and the dawn of pneumatic tire design. Ply cords were originally made from cotton but then progressed to materials such as nylon and polyester for better durability. Rubber compounds also changed through the years to provide better traction and handling, and the bead seat changed a few times until the world settled in on the drop center design during the late 1920s. Despite changes in sizing and ply ratings, these basic principles remained the same from the 1920s through the 1960s. Bias ply tire construction features ply cords that run at a 45-degree angle to the bead and cross over to the corresponding bead. Then, additional layers of ply cords are added and overlapped in a crisscross pattern. The more ply layers are used, the higher the load rating. Four-ply bias ply tires are most often used on passenger cars, and truck tires are typically six plies and higher.
Bias-belted tires came along around 1967 to improve the handling of a bias-ply tire as tread widths began to grow. The same concept of bias ply tire construction remained, but layers of fiberglass belting were placed below the tread surface for added stability. Around this time, the sizing nomenclature also changed from numeric (ex. 670-15) to alphanumeric (ex. F78-15). This change in sizing remained in the mainstream for approximately ten years until metric sizing (ex. P215/70R15) became the industry standard on passenger car tires. The bias-belted tire came during the height of the muscle car era, and some of the most popular bias-belted tires included the Goodyear Polyglas and Firestone Wide Oval.
Radial tires truly changed the handling capabilities of passenger cars and trucks worldwide. Michelin brought radial tires to market in 1948 and refined the concept for years before it became mainstream. The ply cords in a radial tire run at a 90-degree angle to the bead. Modern radial tires feature steel belting beneath the tread, providing strength and stability. The most noticeable advantage of a radial tire is its flexibility and its tendency to absorb imperfections in the road surface. However, there are other advantages, including reduced rolling resistance, which leads to better fuel economy and longer tread life. The increased fuel economy is part of the reason that American auto manufacturers made the switch to radials in the 1970s. For additional reading, you can check out the difference between radial tires and non-radial tires.
Advantages and Disadvantages of Radial & Bias Ply Tires
The question of bias ply vs radial truly comes down to preference, but there are several factors to consider when looking at tire construction types. While bias ply tires are authentic for cars built before 1975, this tire construction doesn’t always produce the best possible ride quality and handling. With bias ply tires, you can expect them to find the grooves and breaks in the road surface, giving you a wandering sensation as you go down the road. This squirrely handling can sometimes be amplified by worn-out suspension and steering components, but it’s no secret that bias ply tires cause your car or truck to move around more than your everyday driver, even in the best-case scenario.
Despite the finicky handling, bias ply tires are best suited if you build a car to match a specific period. Traditional hot rods, gassers, Day 2 muscle cars, and race car restorations fall into this category, as they are often built to replicate a car built in the 1950s, 1960s, and 1970s. Back in the day, hot rodders often used racing tires on their street cars for an even more wow factor. Tires like the Firestone Dirt Track and many types of drag racing tires were used on the street. The poor handling characteristics are exaggerated even further with legitimate racing tires, as they often have race-ready compounds and softer sidewalls. However, today’s Firestone Dirt Track tires are designed for use on traditional hot rods and come with street-friendly compounds and standard sidewalls. They still feature bias ply construction but are now DOT-approved for highway use, whereas modern oval track tires are designed strictly for racing use and should not be driven on the street. Drag Racing Tires vary wildly, from all-out bias ply racing slicks to DOT-approved drag radials, some of which can be driven safely on the street.
The advantages of radial tires are the handling and increased tread life, but the disadvantages can come in the form of fashion. If you’re looking to replicate a particular era, radial tires often upset the vintage look, especially if they’re just generic radials from the department store. A classic car or hot rod deserves a specialty tire, and we’re proud to offer a wide variety of them. Thankfully, there are many great options for vintage-styled radial tires in our product offerings, allowing you to blur the line between vintage bias ply tires and modern radials. Radial tires apply a different type of pressure on the rim, which may cause issues for your classic car, but this article features everything you need to know about mounting radial tires on classic car rims.
FAQ: Radial vs. Bias Ply Tires
Q: Are bias ply tires unsafe?
A: No, unless they are truly old tires. Generally speaking, bias ply tires do affect the handling of a car, but they are constructed using modern materials, making them safe for your vehicle. If a tire is ten or more years old, you should consider replacing them, no matter how many miles have been put on them.
Q: Can I use Bias Ply and Radial Tires on the same vehicle?
A: No. This can cause extreme handling problems, as the bias ply tires and radial tires react differently to surface changes. In some racing applications, bias ply and radial tires are mixed on the same vehicle, but this should not be replicated on the street. Read more: Can I Mix Bias and Radial Tires?
Q: How can I tell a bias ply tire from a radial?
A: Typically, a radial tire will have an R designation in the sizing. It can get a little confusing with some of the modern bias-look radial tires that we offer. In that case, a bias ply tire would feature a size like 6.70-15, while the radial counterpart would say 6.70R15. Another example is alphanumeric sizing, whereas the bias ply tire would read F70-14 and the radial would read FR70-14. Read more: How to Convert Bias-Ply Size to Radial Tire?
Q: What are the differences between bias ply and radial drag tires?
A: The bias ply vs radial drag tires debate often comes down to the car setup. Bias-ply drag racing slicks tend to soak up nearly anything you can throw at them, leaving a little more room for error on the suspension tuning. However, bias ply tires often generate slower elapsed times because of the added rolling resistance. Radial drag tires require a little extra suspension tuning but produce quicker ETs due to the reduced rolling resistance.