Radial tire construction: Overview & maintenance

Radial tires have been the industry standard for a very long time – so long that it seems hard to remember a time when they weren’t, and hard to remember that there are other types of tire construction that are still at least somewhat prevalent for some applications. So, to recap, there are three kinds of tire design: radial, bias and belted-bias. Out of these three designs, radial tires have proven themselves to have plenty of advantages when it comes to wear properties, handling, efficiency and ride quality. Their internal construction is a lot different from older bias or bias-belted designs, however, and we’ll touch on that more shortly.

How are radial tires made?

So what is it about the construction of radial tires that makes them so much different?

From the outside, you’re just looking at the tire’s tread, shoulder, sidewall and casing, and they all look pretty much the same, right? But when you look at the tire’s cross-section, you’ll find steel belts and cord layers that add rigidity and stability to a tire, along with plies that enhance ride quality and durability.

A ply layer attaches to the tire’s bead, which is the strand of cable that runs along the tire’s inner edge, enabling it to have a secure connection to the rim. Plies can be nylon, polyester, rubber, rubberized fabric, Kevlar, steel or other textiles for extra support from the inside out. Without this kind of reinforcement, tires would be too mushy and could easily deform or suffer serious damage. When all the layers of belt packages, plies and rubber subtreads are put together, you have the tire carcass.

In the case of a radial tire, the plies that are arranged on the inside of the tire run horizontally from bead to bead. To put it a different way, radial tire plies run at a 90-degree angle to the direction of the tread.

Benefits of radial tires

Radial tires are designed for ride comfort and responsive, predictable handling, but they also deliver better strength and stability. In older bias-belted tires, where ply layers criss-crossed each other at angles, each subsequent layer deformed slightly and led to friction with other internal layers.

Radial tires do away with that internal friction for less rolling resistance and enhanced fuel efficiency on the highway. This design also accounts for the slight bulge at the bottom of a radial tire, making it look like it could be underinflated even when it’s fully inflated. Part of the ride comfort that’s built into radial tires comes from the fact that 90-degree-angle layers of plies in the sidewall act as a spring, adding a little flexibility and “give” to the tire as it soaks up bumps and irregularities in pavement.

As for lower rolling resistance, that means the engine has to burn less fuel and spend less energy to get the vehicle down the road, and that saves drivers money. Over the decades, radial tires have become such an integral part of overall automotive design (suspension, steering, braking) that they inform automakers’ decisions and vehicle design also informs how tires are made.

Growth of Tire Radials

While most people associate the introduction of radial tires with the 1970s, the first patents for radial tires go back to the 1910s. Ford was the first American automaker to make radial tires standard equipment on the Continental Mark III in 1970. When the first Arab oil embargo hit in the early 70s, Goodyear took the initiative to retool their manufacturing facilities to produce radials. While Goodyear’s management took heavy criticism for that decision, they saw the writing on the wall and knew that radials offered an improvement in safety, fuel economy, and handling.

Drivers at the time were used to the handling, ride, and road manners of bias tires, but it wasn’t long before radials were industry-standard across the board and engineers no longer had to make design decisions around the drawbacks of bias tires. By the early 1980s, there weren’t many who were still wishing they had bias tires (think of someone advocating for VHS tapes over DVD or streaming formats).

Maintaining Tire Radial Tires

It’s easy to forget about tires as long as they’re holding together and getting you from Point A to Point B with no worries. Truth is, though, tires need maintenance as much as any other system on your vehicle. The good news is, that maintenance is actually pretty simple.

• Tire rotations: This is maybe the single best thing you can do for a set of tires. No vehicle has perfect 50/50 front/rear weight distribution, and the forces of acceleration, braking, and cornering shift vehicle weight forward or rearward through inertia. That means that front tires in particular are subject to a different set of forces, and rotating the tires’ positions on the vehicle will help ensure even wear. Manufacturers recommend rotations every 5,000-7,000 miles for correct wear (and require regular rotations as part of warranty coverage). As soon as you have a tire rotation performed, you’ll notice a difference in your car’s handling, braking, and overall road manners from the first time you drive it again.
• Proper inflation: Think about riding a bicycle with a halfway-flat tire. Not much fun, right? It makes the bike’s handling sloppy and makes it feel like you’re always pedaling through wet sand. That’s what it’s like driving on underinflated tires, too. Air molecules will naturally migrate through the valve stem or the rubber sidewalls of a tire, and an underinflated tire means more heat buildup and more friction. Heat is the enemy of any tire, as it causes a lot of stress to the tire’s internal construction just in normal operation and can possibly lead to a dangerous blowout. What’s more, underinflated tires will handle poorly, brake poorly, and cause the vehicle to pull to one side on the highway. You should check your tires’ inflation at least once per month using a good-quality tire pressure gauge, and always remember to check inflation when the tires are completely cold (since air expands when hot and can cause a bad reading). Don’t go with the inflation number that’s stamped on the tire’s sidewall – you can find proper inflation information on the sticker that’s affixed to the driver’s door frame.
• Inspection: You should regularly get a look at the tire’s overall condition. Keep an eye out for excessive wear, uneven wear along a tire edge that can point to an alignment or suspension problem, and any damage or foreign objects in the tread. Run a hand along the tread’s surface and feel for a jagged or “sawtooth” edge to the treads. Look out for cracking, bulges, any areas where the tread may look like it’s starting to separate, or anything else that seems out of the ordinary.

If you have any questions about the best tire maintenance for radials or what in particular you should look out for, there are qualified techs and consultants in just about any good tire shop who can help you out with this information.

Radial versus non-radial tires

On a bias or bias-belted tire, the tire’s casing is built by laying layers of cord over a steel drum, with the layers crossing each other at about a 60-degree angle. These layers of plies are turned up around the bead wire, with the tread and sidewall built over the plies. From there, the “green” tire is loaded over a curing bladder and then put into a mold. As mentioned above, it’s near impossible for the layers to all maintain that exact angle, so the cord plies will all have a somewhat different angle where they attach to the bead (as opposed to their angle directly under the tread).

Today, some motorcycle tires and specialty tires for commercial vehicles still use bias construction. Many special trailer tires use bias design as well, for enhanced load capacity and less tendency to sway at highway speed, but in today’s tire industry radial tires have almost completely replaced bias and bias-belted models.