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Types of tyre carcass
Page 81
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LTHOUGH one takes motor 3hicle tyres for granted, in fact great deal of research and avelopment has been carried it since R. W. Thompson inrited the pneumatic tyre in 945 and J. B. Dunlop fitted e first tyre of this kind to a icle in 1888.
Tyres are either tubed or beless; in the former type, an ner tube is contained in the :tuzl tyre, while in the tubeless iriety, a layer of soft rubber ies the inside of the tyre casing id trns provides a seal between e rTh of the wheel and the re. The rims of wheels innded for tubeless tyres are 3de with a different angle from pse on which tubes are to be ed, so tubeless tyres should t be fitted to wheels which are designed for them.
There are two basic types of e construction, cross-ply (Fig
s 1) and radial-ply (Figure 2. )th these illustrations are produced by permission of mlop Ltd. In the crossply e, which is the older type construction, there are two or )re layers of rayon or nylon rds impregnated with rubber. e oords forming the ply run at angle of about 100 to the rds of the adjoining ply and ch cord is at an angle of prcximately 40 to the bead. The bead consists of a -Oder of strands of steel wire d the ply edges are turned ;r the bead and cemented to It is important to remember en fitting and removing tyres
t the bead is made of metal d virtually inextensible; it inot be stretched to go over wheel rim.
Va'ious tread patterns are :d depending on the ground which the vehicle to which y Bre to be fitted is to be ployed. Prominent tread s, for example, are ideal for t surfaces where they will get maximum grip, but these le tyres may not be suitable high-speed road work where y would wear rapidly and be By.
86 will be seen from Figure 2, the cords of the plies on radial tyres are parallel to one another and arranged radially, that is at 90' to the wheel-rim. In addition to the radial cords, a belt of textile or steel cords Is fitted between the tread and the ply. • These bracing layers act as a belt around the tyre to stabilise the tread and to prevent the tyre from enlarging when it is inflated.
It is claimed that radial tyres give greater tread mileage, etter traction, improved fuel consumption and safer operating than cross-ply. It was stated at a recent Road Transport Engineer's conference. that radial ply tyres fitted to a 32-ton artic would result in a 25 per cent reduction in rolling resistance co-efficient and a saving of six per cent in fuel consumption compared with tyres of cross-ply construction_
Next article: mixing radial and cross-ply tyres.
by Preceptor