Materials and Construction

Materials

Rubber

Obviously rubber is the basic material used in tyre production in either its natural or synthetic form. Natural rubber is harvested from rubber trees. Synthetic rubber is generally produced from the by-products of oil and natural gas. There are now many types of synthetic rubber, all with varying and useful properties which include:

• lower cost
• more robust
• easily manufactured
• airtight

Carbon black

One quarter of the total weight of a tyre is made up from carbon black. Carbon black is a powdery black pigment produced by the incomplete combustion of natural gas. Carbon black strengthens the resistance to wear and tear and is the reinforcing agent of the rubber.

Steel and textile cords

Steel, cotton, rayon, nylon, fiberglass or polyester cords, are specially treated to bond with rubber. They are designed to balance internal inflation pressure and provide the necessary resistance to the various strains that take place when a tyre is in use.

Construction

Components of the tyre carcass:
1. The plies and sidewall rubber.
2. The beads.

Components of the tread area.
3. The tread rubber.
4. The belt package.

1. The plies and sidewalls

In passenger vehicle tyres plies are usually made using polyester, nylon, fiberglass and rayon. Polyester is the most widely used carcass material.

The carcasses of most radial-ply commercial vehicle tyres and some light truck and recreational tyres have steel corded plies. The load carrying capacity of radial tyres, in most cases, is governed by a load index which is a table consisting of numbers with corresponding maximum loads per tyre, in kilograms.

The sidewall requires a rubber that is supple enough to allow flexing and yet provide protection against scuffing, cutting and the elements. A blend of Styrene-Butadiene Rubber is used for this purpose.

2. The beads.

The beads on a tubeless tyre are made to fine tolerances in order to maintain airtightness, where the rim and tyre seal. The bead wires are encased in hard triangular rubber known as bead fillers or flippers. The flipper is designed to provide a smooth transition from the very stiff bead area to the highly flexible sidewall area. The bead heel is the part of the bead that fills the area where the rim flange and the bead seat. Special rubber is used to protect the tyre from chafing against the rim.

3. The tread rubber

The most obvious characteristic required in the tread rubber is resistance to wear. Synthetic rubber, polybutadiene, SBR and natural rubber are used.

Certain modern tyre manufacturers use what they call "cap-and-base" tread construction. This technology allows the manufacturer to laminate two different compounds of rubber, one on top of the other. The compound closest to the steel belt, base rubber, is formulated to resist generating heat, while the top compound, cap rubber, which is in contact with the road, is softer and allows for better grip. Tread design has also been developed and modern trends include the unidirectional design which offers excellent water drainage without sacrificing dry handling and grip.

Another innovation is an asymmetrical tread pattern which has large ribs of rubber on the outside shoulder and smaller ribs on the inside shoulder. The larger ribs on the outside stiffen the tread where the highest lateral load is concentrated during cornering.

Tyre noise, straight line acceleration and cornering are all affected by the tread design and research and development of new ideas is ongoing.The tread blocks on most tyres vary in size in an effort to break up resonance caused when equal sized blocks come into contact with the road surface.

4. The belt package

The belt package consists of bracing cords. The belts are designed to help reinforce the carcass against the internal pressure created by inflation pressure, the centrifugal forces of the tyre rotating at speed, the shocks of bumps and potholes on the road and to enhance lateral stiffness to the tread.