Radial and bias-ply tire structures

Surely on more than one occasion you have heard these terms related to the structure of your tires. Well, today we are going to go deeper into them, and never better said, because to understand what they mean, their differences and how they influence the behavior of our tires, it is necessary to dive inside them.

As many of you know, a tire is not only made of rubber, but it has an internal structure, that is, as if it were a skeleton or a chassis that helps it to support the internal pressure of the air and not break. This structure can be of two types, radial or bias-ply, and its evolution has depended a lot on the change of motorcycles throughout history.

In the past, most vehicles were very heavy and high profile, so they needed tires capable of withstanding the weight without breaking and punctures. To do this, tires required structures reinforced with many ply, i.e. with a diagonal structure. This is synonymous with strength, but also with heavy weight, so that the tires could not perform adequately at high speeds. In addition, these plies created friction with each other with the consequent increase in temperature and danger of tire disintegration.

Over the years, bias-ply carcasses evolved and became lighter until radial carcasses began to be manufactured. These structures maintained rigidity but with less weight, which made it possible to manufacture tires with lower profiles. Nowadays, both constructions are still manufactured and used in motorcycle tires, as each one provides performance depending on the characteristics of the motorcycle, the type of riding of the rider and the kind of use of the tire.

The definition of radial and bias-ply is quite graphic, as it has its origin in the orientation of the plies. In the drawings below you can see how the ply orientation of a radial tire starts from a central point towards the spokes, while the ply structure of a bias-ply tire fills the tire parallel to each other.

As mentioned above, over the years and thanks to the development of technology and materials, each type of construction has evolved. Bias-ply tires have evolved from having only cross ply (made of rayon and nylon) to combining cross ply with stabilizing layers, the Bias Belted, which are placed between the ply and the tread. These layers are usually made of Kevlar and provide more stability when riding.

On the other hand, radial tires have also changed over time, always taking weight reduction and structural stiffness as a premise. A traditional radial construction, which is also widely used in car or truck tires, is based on a radial carcass and a series of stabilizer layers on top of it, which give greater rigidity and rolling comfort. Whereas a more modern construction is based on the radial carcass layer and a continuous steel cord belt that wraps around the tire over the carcass in the form of a circumference. In the example you can see the Radial at 0°, one of the latest and lightest in terms of structure.

To give you an idea, in the following illustration you can see the inside of a radial tire with each of its layers:

The first two layers are reinforcement layers and are intended to give stability to the tire. The third layer is the casing which gives rigidity to the whole structure and retains the internal air between the tire and the rim in the case of tubeless tires. In the case of a tubeless tire, this would be the one that would retain the air. Finally we find the bead rings, which are two coated metal rings that provide rigidity and sealing in the anchoring of the tire to the rim. The materials used in the inner part are usually textiles, such as rayon, nylon or carbon fiber, and metals such as steel.

In short, which is the most suitable? As we said at the beginning of this article, this will depend on several factors such as the characteristics of the motorcycle or the type of riding of the rider. Radials are intended for light road or trail tires, for light motorcycles and in wide sizes and with low profiles. The bias-ply are for road, trail or off-road tires, for motorcycles with narrow rims and high profiles.

If all this has made you curious to know what your tire is like, you can recognize which tire you have by looking at the sizes. For example, on a 120/70 ZR 17, the “R” means it is a radial carcass tire, while on a 150/70 B 17 or 150/70 – 17, the “B” or dash means the carcass construction is bias-ply.