Parts of Tyre | Structure of a Tyre
Parts of tyre
The tyre is made of many different parts that are moulded together to form the complete structure. The parts are built up, one at a time on a collapsible drum. The components of a tyre in the order of assembly are as follows:
1. Liner 4. Tread layer.
2. Cords and plies. 5. Side walls.
3. Beads or ribs. 6. Outer rubber covering
The liner and plies together are sometime called inner casing or carcass. The assembled parts are removed from the drum and bonded together by a process called vulcanizing. In this process, the rubber is heated under pressure to give it the required form and characteristics.
The tyre details can be seen in diagram
Carcass : The carcass gives body and strength to the tyre. The carcass is the tyre without either side wall rubber or tread rubber.
The carcass is made from overlapping piles. Each of the plies consists of parallel cords of rayon, nylon, polyster or fiberglass, embedded in a layer of rubber. The ends of the plies are wound around the beads and bonded to the side walls. Air pressure pushing evenly against the interior surface produces tension in the carcass. Thus the carcass resists and supports the weight of the vehicle. The outer rubber covering is moulded around the carcass.
The liner is a thin air tight layer of rubber that covers the inner surface of the carcass.
The number of piles, layers of cord varies according to the cord varies according to the use of the tyre. Motor car tyres usually have 4 to 6 piles. Heavy duty truck and bus tyres may have upto 22 piles whereas earth moving vehicles use tyres which may have upto 34 piles.
Bead : The bead is a bundle of separate thin steel wires. The bead in the tyre fits around the wheel rim. The wires are often wrapped with a fabric to hold them. The bead is embedded in rubber which serves to prevent the tyre from stretching and thereby leaving the wheel rim.
The greater the load on the tyre, the stronger the bead must be to keep the tyre seated on the rim. The strength of bead is increased either by using a heavier gauge wire or more loops of the wire. These are made of high tensile steel.
The bead also serves as an anchorage for the layers of carcass cords. In some designs, this anchorage is reinforced by additional layers of cord in more or less narrow strips wrapped around the bead. These additional cords extend for a short distance upto the lower side wall and thereby share the severe stresses to which this clinch area around the bead is subjected to.
Tread : The tread is that part of the tyre that is designed to run on the road surface. The tread when assembled, is a separate piece of soft uncured rubber. The tread design is formed by the mould. When vulcanized, the soft rubber is changed to a compound that is highly resistant to wear.
The tread rubber is grooved with a pattern that will provide maximum friction force,and minimum noise, when used on the vehicle application for which it was designed.
In many designs, there are some circumferential ‘belt’ going around the outside of the tyre, between the carcass and the tread layer. This gives additional stability and rigidity to the tread.
Side walls : The side walls are the two strips that connect the bead to the tread. The side wall is made of a different grade of rubber. The quality of this rubber is such as to absorb road shocks, and protect the cord plies. The side walls are relatively thinner. The rubber used to form the side walls, plies and tread are porous in nature.