Basics Of Tyres
It is made up of the following semi-finished products.
- A layer of Airtight synthetic rubber. This layer is found inside the tyre and functions as the modern equivalent of the inner tube.
- The casing ply – This casing is composed of fine textile fiber cords, laid down on straight lines and sandwiched in rubber. These cords are a key element in the structure of a tyre and enable it to resist pressure. In each ply of a car tyre, there are about 1400 cords, each of which can resist a force of 15 kg.
- The lower bead area – Its role is to transmit engine and braking torque from the rim of the tyre through to the contact patch.
- The bead wires – These help to hold the tyre onto the rim. They can bear a load of up to 1800 kg. without the risk of breakage.
- Sidewalls – The supple rubber sidewalls help protect the tyre from shocks that could damage the casing, e.g. Minor shocks against pavements, potholes, etc. There is hard, protection rubber where the tyre joins the rim.
- Bracing plies – Reinforced with very fine, very resistant steel cords, they are crossed obliquely and stuck together. The cords cross the casing cords to form rigid triangles. This is known as triangulation and makes the crown rigid. The plies encircle the entire crown of the tyre and performa very complex role:
- They must be sufficiently rigid around the tyre’s circumference so that they aren’t stretched by centrifugal force, thus controlling the diameter of the tyre under all conditions.
- They must also be rigid transversally to resist the stresses and strains of cornering. At the same time, they must be supple enough in a vertical direction, to “absorb” deformations and other obstacles.
- To obtain these plies, steel has to be stuck to rubber. It is very difficult to do but the perfect cohesion between these dissimilar materials is absolutely essential.
- The radial plies. These plies help to retain a stable profile under the effect of speed and also help to reduce heating up. They are armed with cords, generally of nylon, fitted in single strands or in bands perpendicular to the bracing plies around the tyre’s circumference so as not to stretch under centrifugal force.
- The tread is laid over the bracing plies. This is the patterned part of the tyre which will be in contact with the road. The tread in the contact patch must be able to resist very significant stresses. The treat compound must grip on all types of surface; resist wear and abrasion and heat up as little as possible. All that remains is to mould in the tread pattern and vulcanize these products together to form a perfectly solid structure.