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What are Radial Tires? (Tire Anatomy Simplified)

Posted by Agota Szabo on Jun 27th 2023

What are Radial Tires? (Tire Anatomy Simplified)

What are Radial Tires? (Tire Anatomy Simplified)

Posted by Agota Szabo at Priority Tire on Jun 27th 2023

Radial tires on the road

Tires are the only contact between the road and the vehicle. As such, they hold exceptional importance when it comes to driving safety. Sadly, the importance of their quality is often overlooked.

Over the years, the radial tire alternative became the norm for passenger cars, SUVs, and light trucks. But, what exactly are radial tires?

Stay with us for the ride and let us guide you through everything you need to know about radial tires!

When Were Radial Tires Invented?

Tire design changes constantly, but steel belted radial tires have been a consumer favorite since the 1970s. However, the radial ply tire was not always this popular. There are decades of tire history behind the technology, so let's take a closer look.

The original design for the radial construction of a tire was patented in 1914 in the US, but it did not lead to any products being manufactured. Later in France, in 1941 to be precise, Michelin's researcher Marius Mignol created his own radial tires construction.

Due to Michelin owning Citroen - a European automobile brand - the spread of available radial tires for sale was quick. Their superior performance on passenger cars was instantly recognized in Europe and Asia.

Meanwhile, in the United States, bias ply tires ruled a bit longer. While Europeans were driving around on radial tires, Americans were reluctant to switch from bias plies. Later - thanks to Goodyear's decision to invest and manufacture tires with radial cord plies - the "radial design" managed to conquer the US by the end of the 1970s.

Soon, all motorcars were equipped with radial tire sets, as this technology became the standard. Bias ply tire was left to make way for itself in the specialty tire category. They are still used today for tractors, trailers, off-road (sidewall flexibility), and heavy equipment vehicles (extra load capacity).

What is a Radial Tire? Are All Tires Radial?

Radial tires are characterized by specially placed tire plies in their construction. These tire cords run from one sidewall bead to the other, arranged perpendicularly. Additionally, all radial tires are belted. They feature either steel or polyester cords that strengthen such tires.

Radial tires on a rack

However, both polyester and steel radial tire constructions offer the same positive characteristics. Thanks to the radial tire carcass, such models offer:

  • Less heat is generated along the tire's footprint
  • This promotes a longer tread life and better fuel economy as the pressure affecting the tire is reduced
  • It also offers more stable contact with the road, upgrading handling even at higher speeds
  • The sidewalls flex better, greatly decreasing road vibrations reaching the vehicle's cabin

Unfortunately, even these improved radial tires have their downsides, mainly their repairability. Due to the special car tire structure, radial ply tires are harder to repair compared to diagonal tires. Furthermore, the tire radial structure cannot be fixed on the sidewalls. Only their tread area (excluding the tire shoulders) can be safely repaired.

What does Tire Ply Mean?

So, what are tire plies? This is an extremely important question to answer when talking about any tire.

Tire ply is the cords of the tire's structure layered on top of each other that make up the tire. Technically "What is tire ply?" has multiple meanings. One is the before sentence, as tire plies are the tire cords. However, the other meaning is a bit more complicated.

Back when all car tires were bias ply, the strength of each tire was determined by the number of plies its structure contained. These tires had weaker cotton plies in their structure, so when the stronger radial tire construction trend grew into what it is today, actually counting the number of plies became redundant. This is another lesson in the history of tires.

Does that mean that tire ply is not crucial anymore? NO!

Instead of ditching the tire ply rating, tire manufacturers instead created a rating system they can use. The tire ply rating basically tells drivers the load durability and psi needs of each tire. The actual number of tire plies does not equal their tire ply rating, rather it represents the tire's overall strength and load durability.

How to know what ply a tire is? Most passenger car tires are 4-ply rated. For larger tires, their ply rating will be clearly stated on their sidewall.

A Closer Look at the Radial Tire Anatomy

The tire's plies aren't the only structural elements present in a radial tire. Lots of different elements are hidden under the car tire rubber and all of them are important.

Starting from the beads, you have the bead cords and the bead chaffers, which optimize how to tire lays on the rim. After this, the radial plies and the strengthening steel belts in tires are worth mentioning. These, along with the cap plies keep the tire's ideal shape under pressure. On top of these plies, you will find the tread area, which is manufactured using special rubber compounds, depending on the type of tire you need.

Radial tire structure

Are All Radial Tires Steel Belted Radials?

Nowadays, most tubeless radial tires feature steel belts in their construction. Steel belted tires are manufactured for various vehicles, ensuring their driving safety levels.

Often the steel belt tires are further reinforced with extra materials weaved into the belts. These can include polyester, kevlar, aramid, and other types of materials that help further strengthen radial tire models.

Understanding Radial Tubeless Tires

A tubeless radial tire, unlike most diagonal tires, does not need an inner tube to properly function. Tubeless tires have become the norm for everyday use, but that does not mean that tubed tires have gone extinct.

Still, let's keep the focus on tubeless radials. These tires use the special rubber inner lining of each tire to maintain air pressure. This inner liner, along with the tire's better sealing with the rim, prevents air pressure from leaving the tire, keeping it inflated.

Radial tubeless tires can also be used for agricultural, construction, and industrial applications. While they do not perform well with low air pressure levels, bias-look radial tires help keep ground compaction to a minimum. They are able to perform as well as bias-ply tires can, which is why their popularity is growing in these fields.

Tubeless vs tubed radial tires

Radial vs Bias Ply Tires (The Two Main Construction Types)

The two main tire construction types are radial and bias-ply tires. While radial tires are more popular, in specific applications, a bias or diagonal tire set will still perform better.

What's important to remember is this: Do not use radial tires with any other type of tire on the same vehicle because they do not feature the same construction and it can lead to structural and vehicle damage.

What are Bias Ply Tires?

Non-radial tires, or bias models, were the original construction tires used in the automotive industry. These tires feature plies that are placed diagonally (at a 45-degree angle) from one bead to the other. This gives them higher load durability and better damage resistance. But, this comes at a cost.

The difference between radial and bias tires is the way their structural plies are placed. Yet, this ply placement results in great distinctness between the two different ply tires.

When talking about radial vs bias ply, heat resistance is a huge topic. Due to the versatile ply placement of these tires, they do not handle heat accumulation in the same manner. As mentioned before, radial direction ply placement offers heat buildup resistance.

On the other hand, bias-ply tires tend to heat up a lot more under driving pressure. This also results in worse fuel economy and shortened tread life for them. The advantage that bias plies offer is their damage resistance even at low air pressure. They also come with rigid sidewalls that guarantee high load capacity.

Radial vs Bias tires internal structures

But there's is a lot more to compare and contrast between radial vs bias ply tires, as it is another extensive topic when it comes to tire structure.

Frequently Asked Questions

Are radial tires good for trailers?

Depending on what you use your trailer for, a radial tire set can work for you. All season radial tires are often mounted on trailers due to their heat resistance, surface contact, and load durability. They are better for trailers dealing with larger loads for longer periods of time, while also ensuring a fuel-efficient performance.

Do radial tires have a ply rating?

Yes, every radial tire manufactured for passenger cars, SUVs, light or commercial trucks has a ply rating. While structural tire layers are not counted like they used to be, these tires still receive a ply rating that indicates their overall load durability. The higher the ply rating, the more load each individual tire can handle.

Do radial tires have a direction?

While some radial tires are directional, this is not true for all of them. Just because a tire features a radial ply construction does not mean that it has to be mounted on the vehicle in a specific direction. Whether tires are directional or not depends on multiple other factors, not just on radial cords.

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