HIGH SPEEDS

Auckland Star, Volume LXXIII, Issue 178, 30 July 1942, Page 6

HIGH SPEEDS

EFFECT ON TYRES

ADVICE TO CAR OWNERS

It is generally recognised that high speed increases the rate of tread wear and motorists interviewed today are of opinion that the regulations fixing a maximum speed limit of 40 miles an hour for all motor transport is a common sense proposal that should have been put into effect as soon as the rubber position became known.

When cars travel at high speeds the increased wear on tyres is due to the lower resistance of the tread stock to abrasion due to its higher temperature. High speed causes the tyres to strike road obstacles more severely and spinning and grinding of the tread against the surface of the road occurs much more frequently and to a much greater degree than at lower speed. Tests made at the Washington State College experimental station show that a car travelling at 30 miles an hour will cause 12 per cent more tyre tread wear than a car travelling at 20 miles an hour, whi'e at 40 miles an hour the same car would increase the tread wear to 43 per cent. Braking also affects tread wear. This can be regarded from three standpoints: frequency of application, severity of operation, and lack of equalisation and adjustment.

Under-inflation is one of the worst enemies to satisfactory tread wear. The under-inflated tyre runs hotter, thereby reducing the ability of the tread to resist wear. Furthermore, an excessive "scuffing" action is produced where the tread comes in contact with the road. Better Mileage Mr. A. U. Wells, manager of Firestone Tyre Distributors, said to-day that owners of private cars could get a better mileage out of their tyres if they paid greater attention to inflation. "Cars are not used as much as formerly owing to petrol and other restrictions," he said. "It is more necessary, therefore, to keep the tyres, at the. correct inflation figure. Many users seem to overlook this precaution." He also warned that motorists should avoid hitting kerbs or coming to rest against them. He advised owners to change their tyres round once every 1000 miles and to give immediate attention to leaking tubes. Truck users with dual tyres should be careful to see that their rubbers were carefully paired. If one tyre were well worn and another new, the new tyre would carry the greater part of the load. Cuts and fractures should be attended to promptly as water getting into them rotted the tyre carcase. Wheel alignment was also important. Loose bearings, worn bushings, loose steering connections and bent axles all had an effect on tyre wear and should be rectified if rubber were to be conserved. Army Vehicles "No reasonable motorist will take exception to the restriction of 40 miles an hour imposed by regulation specifically for the purpose of conserving rubber." said Mr. F. G. Farrell. president of the Automobile Association, to-day. "Anv provision that will give lonsrer life to tyres is definitely in the interest of motor users themselves." As far as the exemptions were concerned he thought they should apply only in cases of necessity. There were many occasions, for instance, on which military vehicles could carry out their normal duties without exceeding a speed of 40 miles an hour. Complaints concerning excessive speed of army vehicles and vehicles of army contractors were still being received. It ; seemed even more essential that the tyres of those vehicles should be made to last as long as possible. In case of an emergency all restrictions would, of course, have to go by the board.

Recent tests by tyre manufacturers demonstrate how overloading and under-inflation affect tyre mileage. A chart has been prepared which shows that 20 per cent of overload or 80 per cent (instead of 100 per cent) inflation reduces mileage by 30 per cent; 40 per cent overload or 71 per cent inflation reduces mileage by half; 60 per cent overload or 64 per cent inflation reduces mileage by 61 per cent. With 100 per cent overload or 45 per cent inflation only one quarter of the normal mileage can be travelled.