SHOCK-ABSORBING TYRES

New Zealand Times, Volume LIII, Issue 12423, 17 April 1926, Page 18

SHOCK-ABSORBING TYRES

THE SERVICE OF RUBBER MUCH DEPENDS ON ROADS. In all motor tyres rubber forms at least "part of, a device whose chief function is to absorb shocks. This fact, coupled with the common knowledge that rubber is a good shock absorber under any circumstances, naturally, leads to the idea that the rubber portion of a pneumatic tyro plays a larger part in the shock-absorbing action of the tyre than it really does. In the case of a solid tyre the rubber does not compress very much, even under heavy load and great shock, the quality and hardness of rubber necessary for tyre construction being BUch that the compressibility of the tyre is very small. If a thick solid-rubber tyre compresses only slightly, it is obvious that the thin, tube and comparatively thin cover of a pneumatic tyre will bp compressible by quite a small ampunt, and the shock-absortiin g powers of the rubber due to its compressibility will be negligible. MOST SUITABLE' MATERIAL The chief reason why rubber is so necessary at the present time for tyre manufacture is that it is ■ the most suitable' material for the purpose, on account of its being, when in normal condition, airproof and waterproof, fairly strong, very flexible, a good gripping medium, and adaptable to manufacturing processes. Its chief functions in a pneumatic tyre are to contain the air and to stand, rapid and almost continual deflection without becoming permanently flefortned or stretched, to be unaffected by moisture under normal conditions, and to give a good grip on the road. These properties are not easily found com-

bined in any one other material, and it is because of them that rubber is chiefly used fdr pneumatic tyres, and not because of its own sho9k-absorbing qualities. Practically all of the shockabsorbing qualities of a pneumatic tyre depend upon the way in which the air is-used. j TYRE PRESSURE A FACTOR The whole value of a tyre as \ a ehock-absorber depends upon the amount of compression, that will take place under a given load. Increasing the air pressure will make the tyre less resilient, undoubtedly, but the tyre’s useful range of efficiency as an absorber of severe shocks will, be increased. Although the light shocks may not be so well absorbed, the heavier shocksj more in need of attention, will be more thoroughly absorbed.. Tyre pumping pressures must he dictated by individual requirements, however: no hard and fast rules can be laid down. On good roads pressures may vary between quite wide limits, with’ satisfactory results. With fairly uniform but moderately rough roads, having no severe stretches, probably the lower pressure would he the more suitable; whilst for running on roads having a fair amount of really hard surface, the higher pressures would seem most suitable. In deciding on tyre pressures,, consideration must be- given to the various factors which influence "tyre efficiency, including load, running conditions, tyre site, etc,, if the best results are to he obtained.