SLOWER SPEED SELFIMPOSED

Dominion, Volume 35, Issue 259, 31 July 1942, Page 4

SLOWER SPEED SELFIMPOSED

Drivers Learn Lesson The maximum speed limit of 40 miles an hour introduced to save tyres and ix’trol has already been imposed by most motorists, according to Mr. W. A. Sutherland, (secretary of the Automobile Association (Wellington). Though in ths early days of petrol rationing when traffic density was* reduced there had been a tendency to Increase speeds, slower motoring had been evident during the past few months, >he considered. Drivel's had learnt by practical experience what trained scientists in the laboratories of tyre manufacturers had discovered.

“Research shows conclusively Unit speed leads not only to increased petrol consumption but to more wear on tyres through friction and alsu through wear by sudden braking. Any concrete road will show the blaclt marks of tyre rubber scraped, off when a car has slowed suddenly from a hlgl) speed. Quick acceleration has 3’ similar effect,” he said. “It is now generally recognized that the modern car gives the best performance for rubber aud petrol al a speed of 35 miles an hour. Reseafeh, chiefly in America, shows that if this is taken as the norm for 100 per. cent, tyre mileage, the loss witli increased speed is as follows: 40 m.p.h., 88 per cent, efficiency; 45 m.p.h., 78 per cent.; 50 m.p.h., 67 per cent.; 55 m.p.h., 55 per, cent. Slower speeds, though not so satisfactory mechanically, give .a corresponding increase in the life of tyres. At 30 m.p.h. efficiency can be measured tis Hl per cent, nnd at 25 m.p.h. at 120 per cent. Soft Ride and Short.

“Another cause of rapid tyre deterioration is neglect to maintain a proper standard of iutlatiom Those experienced with tyres consider that It is preferable to maintain a pressure above that recommended by the manufacturers rather than one lower. Soft tyres give a comfortable ride, but it. is a short one, The engineer of the Automobile Association (Auckland), Mr. G. U. Robertson, said recently that there was a 10 h.p. car in Auckland which- had travelled 28,000 miles on one set of tyres which were still in good condition. This was the direct result of a constant pressure of. 301 b. “Experiments show . that if 301 b. is taken as the most satisfactory pressure for maximum tyre life, 251 b. pressure will result in a loss of 32 per cent, in mileage, 241 b. in 38 per cent, loss, and 211 b. in 52 per cent. loss. “Cornering at speed is another common cause of tyre deterioration, as is the parking of vehicles with the edge of the kerb biting into a tyre. This is not so common as it used to'be, but cases can be observed every day of this neglect. Another fault is that of overloading small cars.”