What To Know About Belted Tires

Rubber has always been the primary material in tire construction, going back to the early automotive days. Over the years, tire construction has evolved alongside improved manufacturing techniques and a greater emphasis on durability and driver safety. Today, almost every tire has an internal structure that’s encased by rubber.  

Internal tire composition changes, depending on the tire type. For example, radial tires contain steel belts that run around the circumference of the tire beneath the tread, to increase stability and improve tread life. The plies beneath them run radially from bead to bead.

Another design is a bias ply tire, which has plies that are arranged diagonally across the tire. A hybrid of bias and radial tires, called belted bias tires, do incorporate reinforcing belts. 

What Are Tire Belts?

A belted tire is one that contains a layer of reinforcing steel belts or cords beneath the tread. If you were to cut into the tread of a tire, you would find a layer of rubber on the outside that makes up the tread, then a “belt” made from steel, nylon, or other reinforcing material. This belt is part of the internal structure of the tire, as the bottom-most inner layer is usually an inner liner of rubber that helps hold air pressure. 

Do all tires have belts? Yes, most modern passenger and light truck tires have belts. The variation between tires comes mainly from the type of material used. Steel is the most common. Nylon is another option, which may be used in place of or to reinforce steel belts, because it offers flexibility and heat resistance. Specialty tires, such as motorcycle, agriculture and industrial applications don’t typically use belted construction. 

Some tires have multiple layers of belts. If you were wondering why the word “ply” is used for both tires and paper towels, it’s because ply refers to the layers of material. Ply refers to the number of layers in a tire’s structure, not the number of belts, so a higher ply rating means the tire can carry more weight, not that it has more belts. 

Are belted tires better than regular tires?

Belted tires are regular tires. The vast majority of modern applications (passenger and light truck vehicles) use belted tires.

Are belted bias-ply tires better than unbelted bias-ply tires?

Yes, belted tires improve handling, durability, and tread life. Not only are belted tires more stable, but they’re also safer as they help maintain tread shape at high speeds. Tires for modern passenger vehicles all contain some sort of internal construction to help their stability. 

Are belted radial tires better than bias-ply tires?

Yes, radial tires provide better traction, longer tread life and a smoother ride than bias ply tires, especially for passenger vehicles. 

Why would someone want unbelted tires?

Non-belted tires are used in specialty applications such as some agriculture, aircraft landing gear, low-speed industrial equipment — and even RC cars!

What Are Bias Ply vs. Radial Tires?

So, given that most modern passenger tires have belts, are there different types of belted designs? Well, the variety comes in how many layers of belts, the material used, and the pattern of the belts. We hinted at them earlier, but let's briefly go over bias vs radial tires. 

Bias ply tires

A bias ply tire has multiple layers (not belts) in a criss-cross pattern diagonal to the tire. These are not belts, but body plies that provide structural support. Learn more about how bias ply tires work here.

The benefit of a bias ply tire is that it’s very durable and an excellent choice for vehicles that need a higher load capacity. 

Radial tires

A radial tire has body plies that run radially (bead to bead) and steel belts that run the circumference of the treads. All radial tires include belts, but what makes them “radial” is the direction of the body plies, which run straight across from bead to bead. The design reduces friction between plies, which reduces heat buildup. Learn more about radial tires here.

With a radial tire, the benefit is less friction and heat, which means less vibration during driving. Radial tires are a bit more comfortable to drive on than other designs. 

What Are Tire Belts Made Of?

The layers of tire belts are constructed with:

• Steel: Improves the strength of a tire but is also known for having a higher cost than fabric-based alternatives.
• Polyester or nylon: A synthetic fabric that’s more flexible and cheaper than steel, but offers less rigidity than steel. Nylon often reinforces steel belts, while polyester is more common in body plies. 
• Fiberglass: A material option that’s rarely usually used in modern passenger tire production, because of durability concerns. 
• Kevlar: Usually only found with more expensive, high-performance tires because of its strong but lightweight structure. 

How do you know what your tires are made of? You may be able to deduce it by looking up the manufacturer’s specs and using a DOT number as a reference. For everyday passenger vehicles, belts and plies aren’t major concerns, but commercial truck and trailer drivers may want to do the extra research to get a sense of their tires’ durability and load rating.

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