Radial and bias-ply tire structures
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.
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.
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.
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