RAPID TIRE WEAR

Evening Post, Volume CXIX, Issue 110, 11 May 1935, Page 32

RAPID TIRE WEAR

THE PRINCIPAL FACTORS

KEY TO ECONOMY

There were three major .developments in car design last year, any one of which represented more departure from the conventional than all chassis changes of the previous five years combined. These three developments were: (1) Independent front wheel springing; (2) redistribution of weight between front and rear axles, with a corresponding change in the percentage of braking on front and rear wheels; (3) changes in the aerodynamic shape of car bodies, including increased shrouding and shielding of tires by fenders and side plates. In general, faster tire wear has been experienced, and it is important that the various factors which contribute to this situation should be recognised The following information covers the more important of them:

1 Speed.—Authorities agree, after many tests, that tire wear, on the average, is increased from three to five fold, for a twofold increase of car speed. One of these tests shows that tire wear at 50 miles an hour is more than twice as fast as at 35 miles an hour. Another recent test shows that tire wear at 70 miles an hour is 42 per cent faster than at 60 miles an hour Both because of car design and road conditions, average driving speeds have risen.' It is fast drivers who complain most of rapid treadwear.

Higher Speed on Curves.—The case here is even more striking. Modern cars not only have the power to take curves fast, but a lower centre of gravity, nicely poised steering, and anti-roll stabilisers, all of which factors permit a driver to negotiate curves at speeds which would have been ■ impossible five years ago. Tire wear) is violently enhanced^

- More Abrasive Roads.—As roads are renovated or new roads built, there is a definite trend towards surfaces and constructions of increased abrasive quality. The aim is to reduce slipperiness of the surface, but abrasiveness necessarily follows. Tests have shown present-day surfacing to be from 30 to 35 per cent, more abrasive than previous types of roads.

Brakes.—With the increased speed and engine power of modern cars, more powerful and adequate braking has been fitted. Quicker stops can be made, but wear and tear is heavier. Tests show that extra applications of brakes, if made only once in five miles, increase the rate of tread wear by from 30 to 40 per cent. Congested traffic conditions in cities have greatly increased the necessity, for quick and frequent application ,of ■ brakes', and it has been found "that this vigorous use of brakes not only increases the rate .of tread wear, but also enhances the; peculiar and irregular types of front tire wear.

Inflation - Pressures.—Lower and lower inflation pressures are used for the sake of easier.'ride. With any type of tire or of tread compound, the lower the pressure the faster the treao 1 wear, because with the lower pressure there is more tread area scrubbing and grinding against the road. Numerous tests have shown that a 10 per cent, reduction in pressure causes 15 to 20 per cent, increase in rate of wear, and 25 per cent pressure reduction increases the rate of wear 30 to 50 per cent. These relationships depend on cat design, steering, weight distribution, and other factors, but no matter what the circumstances one always pays for easier ride;in faster tread wear.

Decreased Wheel Diameters.—The steady ; trend towards the use of smaller diameter wheels on motorcars has been another contributing cause of rapid tread wear.

The preceding covers the principal factors responsible for fast tread wear. 'With all these factors having great individual effect on tire wear, it is inevitable.that a wider and wider gap should appear between the milages obtained by different drivers. The conservative type of driver enjoys greater tire milages than before, due to improvements that have been made in tire construction, but the fast or careless type of driver pays for his speed and carelessness with poor tread milage. Considering that all the forces of driving ,and stopping and of lateral control are concentrated and focused in the small area of contact between tire and road, it is not surprising that there is a vast. difference. befayeen driving at 25 miles'per hour and 75 This threefold range of speed actually means a ninefold range of .force to be handled by the tires. Tire milages will vary from 5000 to. 40,000, depend,ing upon the care or abuse to which the equipment is subjected. :