1 4. WHEEL AND TYER 4.1 Introduction The wheel, along with the tyre has to take the vehicle load provide a cushioning effect, and cope with the steering control. The various requirements of an automobile wheel are:- 1.It should be lightest possible so that the unstrung weight is least. 2.It should be balanced both statically as well as dynamically. 3.It should be possible to remove or mount the wheel easily. 4.Its material should not deteriorate with weathering and age. 5.Good ability of heat dissipation (frictional braking heat). 4.2Tyre A tyre is a cushion provided with an automobile wheel. It consists of mainly the outer cover and the inner tube. The tyre tube assembly is mounted over the wheel rim. It is the air inside the tube that carries the entire load and provides the cushion. The tyre performs the following functions; 1.Supports the vehicle load. 2.Provides cushion against shocks. 3.Transmits driving and braking forces to the road. 4.Provides cornering power for smooth steering. 4.2.1 Tyre Construction(I) Carcass (casing): The carcass is the frame work of the tire, it must be rigid enough to hold in the high pressure air, yet flexible enough to absorb load changes and impact. It consists of layer of tyre cords bonded together with rubber. Tyres are generally classified, according to the direction of the cords, into radial-ply and bias ply types. (ii) Tread: The tread is an external rubber layer protecting the carcass from wears and external damage caused by the road surface. It is the part that directly contacts the road and generates the attractive resistance that transmits the vehicles driving and braking forces to the road. The tread pattern consists of grooves molded into the tread surface, and is designed to help the tyre more effectively transmit these forces to the road. (III). Side Walls: The side walls are rubber layer that cover the sides of the tyre and protect the carcass from external damage. The largest, most flexible tyre constituents continuously flex under the loads applied during travel. They bear the manufacturer's name, tyre size, and other information. (IV). Breaker: The breaker, a fabric layer between the carcass and the tread, reinforces the adhesion between the two, while helping to attenuate the shocks passed from the road to carcass. Breakers are commonly used in bias ply tires.
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