If you own a classic car built before 1975 or thereabouts, you’ve probably thought about moving to radial tires. There are several reasons to do so – but there are also a couple of caveats to consider. Should you put your classic car on radial tires? What about the new “Bias-look radials” being manufactured specifically for classic cars? Are they the right choice?

Bias-ply vs. Radial: What’s The Difference?

Until the Seventies, the vast majority of tires fitted to cars in the United States were “bias-ply”. The name comes from the construction method, in which “plies”, or layers of cords, run from bead to bead at a 45-degree angle. (This angle is “on the bias”, thus the name.) The plies are criss-crossed for strength and durability.

Bias-ply tires, which are still in wide use for heavy-duty trucks and other commercial vehicles, have a distinct look to them from their rigid and narrow construction. They usually look like they have more air pressure in them than a radial inflated to the same spec, because there is less “give” to the construction.

This lack of “give” has a few other effects of which we should be conscious. The first is overall grip, which is almost always much lower. (Imagine a curved-dash Olds going through a turn, followed by a modern Corvette!) The second is road compliance. Bias-ply tires don’t ride as well, and they transmit loads to the suspension differently. Perhaps the most important is how they affect the wheels on which they are mounted. Bias-ply tires transmit much less force to the beads on their wheels.

Modern radial tires, by contrast, have fewer layers – or even a single layer – of cords running perpendicular from bead to bead across the face of the tire. This makes them far more flexible. As a consequence, they have much greater grip, much better road feel, and much more cornering ability – but they are also much harder on their wheels.

The case for bias-ply

For many years, the reason to run bias-ply tires on our classics was obvious: it was all we could get! That’s still the case for some older vehicles, and in that case you’re stuck with bias-plys. Even among drivers who have the choice, however, many still stick with bias-plys, and there’s a reason for that: aesthetics.

Radial tires just don’t “look right” on many older cars. The profile is all wrong, they look “flat”, and they destroy the visual authenticity of a classic. For 100-point restorations and serious vintage-event participants, that’s the only reason they need to consider.

It’s also the case that many genuine or original-spec wheels can’t properly handle radial tires, which may lead to an increased risk of wheel failure at speed. Nobody wants that. Last but not least, there’s the undeniable fact that increased tire grip leads to increased loads on the suspension and even the frame. If you’re cornering a 1955 Chevrolet on radials, you’re putting forces into the car that the engineers didn’t plan for. Is that really a good idea?

The case for radial

All of the above are valid concerns – but many owners still choose radials for their vintage cars, citing what we call “dynamic safety”. Which refers to turning and stopping, as opposed to the “passive safety” of an airbag or seatbelt. You’ve probably noticed that speeds on American roads are up quite a bit since the Fifties. Nobody on Route 66 was averaging 80 or even 85mph the way a lot of traffic is today. People are more likely to tailgate in traffic, brake suddenly, and rely on the sophisticated safety systems in their modern cars to sort it all out after the fact.

Radial tires turn and stop better. The difference is particularly pronounced in bad weather; a lot of radial tires feel completely secure on wet roads at speeds which would have a bias-ply-shod car upside-down in the ditch. If it’s raining outside, and a deer crosses the road ahead of you, chances are you’ll be better off with radials.

As for the concerns about wheel and suspension construction? A lot of drivers are simply putting new, radial-capable wheels on their classics, and moderating their speed via self-control instead of waiting for the car to fishtail sideways. As experienced motorcyclists often say, “The throttle works both ways.”

Enter the bias-look radial

Thirty years ago, Coker Tire developed the Coker Classic, which fit many bias-ply applications while offering the construction and safety of a radial. It’s been a very popular choice ever since, even though you might have to change wheels to get the full advantage of it.

Now there’s a new generation of tires, led by the Coker American Classic “bias-look radial”. This tire has the narrow tread, bulged sidewall, and sizing options of traditional bias-ply tires. For Thirties-centric drivers, there’s now the Excelsior Stahl Sport Radial tire. Again, you might need a new wheel to make it work, but the look will be far more period-correct, while offering many of the advantages we associate with radial tires in the modern era.

That covers cars up to the Sixties and Seventies – but what about these more modern cars, which can often run a modern tire size and have, in the “pro-touring” community, frequently been fitted with low-profile radials?

Seeing it as a system

It helps if you look at your tires as just one part of the entire suspension system, the way a Formula 1 team might. Your suspension should be adapted to the behavior of your tires, and the whole thing should work as a unified whole. That means choosing suspension components that are up to the task of a modern tire.

Once you have the “system” mindset, then a lot of decisions make themselves. Are you going for a bias-look radial, or one explicitly designed for the classic car market? Chances are that you can get by with the appropriate wheels and an exhaustive check to make sure your suspension is operating at like-new levels of capability. Want to increase grip? You’ll need to trace where the resulting forces go. This can mean anything from better wheel bearings to a complete swap-out for a double-wishbone suspension.

But no matter which choice you make, you should…

Looking at your car as a complete system will help you make the right choices – but no matter which choice you make, it’s important to avoid the mistake that many classic and collector car owners make, which is letting their tires get too old.

It’s true that tires wear out when you drive them. That’s obvious. Less obvious is the fact that tires wear out when you don’t drive them. Sunlight and even indoor artificial light imparts UV radiation to rubber tires, leading them to harden, become brittle, and crack. Air pressure and humidity inside the tire can rot the rubber and rust the belts. Sitting in one place for a long time can damage the integrity of the tire structure. Which is why you should note and observe the construction date on the tire, then follow the manufacturer guidelines for replacement. We know that there’s nothing more frustrating than replacing a set of “brand-new” tires. But the safety implications are very serious.

So make your choice, whether it’s based on looks, usability, or both – then make a plan to keep your rolling stock current. Doing that will prepare you for many great miles ahead, no matter what you decide.