COSTLY SPEED

Rotorua Morning Post, Volume 2, Issue 538, 23 May 1933, Page 2

COSTLY SPEED

SLIPPAGE CUTS UP TYRES UNDER FAST _ ' TRAVEL. " INTERE STING TESTSt Speed has always to be paid for, a fact that sooner or later is realised by all motorists who indulge in fast travel on the road. Th&nks to the great improvement effected; in tyre construction during recent years, thie cost of speed is .not so'high to-day as in the days when tyres 'practically disintegrated under the stresses and heat of sustaihed high speed. Although tyres now better withstand hard driving, the relation between car speed and power transmitted by the driving tyres, "is still the factor- that plays the most important part in tyre longevity. Tests have proved that when a car is travelling at 30 m.p.h. on a sm'ooth, level road, the energy exerted. by the rear wheels against the road is 5.1 i h.p., at 40 m.p.h. the power expended is 9.6 h.p., at 50 m.p.h. 16.1 h.p., at60 m.p.h. 25.5 h.p:, and at 70 m.p.h. 33.3 h.p. From this, says Dunlop-Perdiau, it will be seen that an increase of from 30 to 40 m.p.h. in6ans an increase of 88 per cent. in the power which the driving tyres must transmit or expend through skin-friction between "tyres and road. Every ounce of power transmitted by the tyres tends to t produce slippage of the driving tyres against the road, and the higher the speed travelled the greater the slippage and consequently the greater the tyre wear. That is why the forces of friction and retardation are better transmitted when driving on well de^ffiied non-skid ' "treads, as against treads that are worn quite smooth. '.Road slippage really accounts for the diiference in tyre mileages obtained by motorists who are satisfied with' a moderate speed, and the dlivers who habitually travel fast.