Tread Depth Important

Press, Volume CIX, Issue 32031, 4 July 1969, Page 9

Tread Depth Important

By adopting a minimum tyre tread depth standard of one-sixteenth of an inch New Zealand has followed the policy of other roadsafety conscious countries which have become increasingly aware of the dangers associated with worn tyres, says the latest issue of the “Atlantic Marketer.”

Only 0.4 per cent of 60,000 fatal and injury accidents investigated by the California Highway Patrol in 1967 were caused by tyre failure, but there is increasing evidence that while it is not tyre failure that causes many accidents in many cases the tyres being used are worn..

A worn tyre does not provide nearly as much adhesion as one with a reasonable amount of tread, and if the road is wet it provides virtually no grip at all. Light rain will cover a road surface with water to a depth of one-fifteenth of an inch, and on this surface a

new tyre will retain 82 per cent of the grip it has in dry conditions. But a tyre with only one twenty-fifth of an inch of tread will retain only 35 per cent of its grip.

A normal tyre is called on to remove about 2.5 gallons of water a second from the road surface when a car is travelling at 60 m.p.h„ the article says. If there is insufficient tread depth the stage can be reached where the front wheels ride up on a cushion of water, leaving the driver with no steering or braking control. This is known as aquaplaning, and when it occurs the front wheels can be stopped by applying the brakes, but the car will continue at undiminished speed because there is no contact between the wheels and the road.

Apart from the safety aspect, manufacturers believe that the legislation will make motorists more tyre conscious,

the article says. Some believe motorists will take more care of their tyres and get longer life from them than in the past. “Many New Zealand motorists get nothing like the wear that they should from their tyres, simply because they do not maintain them properly,” a spokesman for one tyre company said. The cardinal rule is to check the tyres at least once a week to ensure that they are at the correct pressure, and this check should be made when the tyres are cold, not after a run. Under-inflation causes flexing, which increases tread wear and puts undue strain on the tyre casing. Car handling will also be adversely affected. Over-inflation reduces the cushioning effect of the tyre, causes rapid wear in the centre of the tread, and makes the tyre more susceptible to concussion damage.

It is wise to remove flints, stones or other objects which become imbedded in tyre treads. Oil and grease can cause tyre damage and should be removed immediately. Manufacturers advise motorists to give their tyres a good scrubbing when they wash their car.