THE CARE OF THE TYRES

NZ Truth, Issue 1227, 6 June 1929, Page 19

THE CARE OF THE TYRES

It Is Always Better To Test Them Regularly Every Week

INCORRECT AIR PRESSURES Many motorists are most illogical m the way they regard their, tyres. So much is expected m the way of long, useful life, but little is given beyond infrequent attention to pressures.

'THE result is that motorists who pay * attention to their tyres invaviably obtain satisfactory mileage. The remedy for most tyre troubles is to be found m the slogan, "Test your tyres every Friday." / The whole load of a car Is supported - by the air contained m the tyres, and if the pressure Js not sufficient for the load undue wear of the treads of the tyres takes place, though it may not at first 'be quite clear why this is so. The tread surface should be m rolling contact and not m rubbing- contact with -the road, and the load should be carried mainly on the centre of the tread. When the air pressure is insufficient the outer cover is distorted excessively underload, and this causes a bunching, or "wiping," movement of the tread. In these circumstances the sides of the tread not only take most of the load, but are also being continually scraped over the road surface owing to the wiping movement. In the case of an under-inflated tyre fitted to a canted front wheel this "wiping" on the road causes the tread on one side to be worn very much more quickly than that on the other. Even with correctly inflated tyres, uneven wear will be accentuated by canted wheels. The obvious cure is to change over the tyres every 2000 miles or so, and this is one of the first points to observe to x obtain the maximum mileage from covers m use on the front wheels. If a tyre is not inflated to an adequate pressure for the load it carries, the slightest wheel irregularity will re-

suit m unequal tread wear m some form or, other. Immediately the trouble is noticed, the wheel carrying (the tyre m question should be jacked up and its running carefully checked. Tyres on front wheels are particularly liable to wear irregularly m this way if there is looseness m the steering-. Too much stress cannot be placed on the fact that with a car m good mechanical condition the mileage obtained from the tyres is dependent, first, upon the maintenance of correct inflation pressures, and, secondly, upon the kind of road surface over which the car is most frequently run. . One of the leading tyre manufacturers contends that m 100 tyres of the same size and type the potential mileage varies only by about 5 per cent. The actual mileage obtained thus depends upon differences m running conditions. The result of tests carried out shows that the rate of tread wear at 50 m.p.h. is double that at 30 m.p.h., even on a good road, and the moral should be obvious. Other interesting tests have been carried out with tyres of the same size and type, used on exactly the same kind of cars, but over asphalted roads m one case, and waterbound macadam roads m the other. Negligible wear of the tread pattern was evident m the case of the tyres which ran 4300 miles over asphalt roads, while m the second case only 1400 miles was sufficient to wear away nearly half of the tread pattern. These tests showed how vital it is to bear m mind average speeds and road conditions when comparing tyre mileage.