DEEPER TYRE TREADS

Press, Volume CIX, Issue 31983, 9 May 1969, Page 9

DEEPER TYRE TREADS

Increasing the tread depth of new and retreaded tyres to compensate for the one-sixteenth of an inch minimum depth allowed by law would do little to improve tyre life, and would lead to other problems, tyre companies report. It would also mean using more rubber in a tyre, which would increase the cost of tyres for little real benefit In any event, the tread on New Zealand-made tyres is already deeper than on some overseas tyres, notably those made in the United States. Nor does tread depth always bear a direct relationship to the wearing properties of a tyre. Radial-ply tyres, for instance, have a shallower tread than crossply tyres, but they last up to twice as long. The thicker the tread, the more unstable it is, and the more it moves in relation to the casing. As a result it wears more quickly, and the flexing causes heat troubles which can lead to tyre failures.

Assuming a tyre lasts for 20,000 miles from the time it is new until it is bald—and on some cars the tyres would not last as long—one-six-teenth of an inch of tread would represent about 3500 miles.

It might last a little longer than this, because the thinner the tread the more stable it is, and the less quickly it tends to wear. But they would certainly be risky miles.

THIN TREAD The thinner the tread, the more easily the tyre is punctured. But from a safety aspect, research shows that a tyre’s braking effect on a wet surface falls drastically when the tread-depth reaches about one-sixteenth of an inch. There is too little tread to carry away the water from between the tyre and the road, and water is an excellent lubricant for rubber. In addition there is the danger of aquaplaning at speed: the tyre cannot get rid of water, and rides on top of it, losing all contact with the road.

Manufacturers could now make tyres with hard treads which would last much longer than present-day tyres, but such tyres would have very poor grip, particularly on wet roads, and would give a very hard ride. A balance must be struck between good grip and good wearing properties. BENEFIT

A benefit of the new regulations is that motorists will now be far more likely to find their worn tyres are suitable for retreading. Tyres run until they are bald, or almost

so, are very prone to damage which precludes retreading. A county councillor was recently reported in "The Press” as saying that the new tread-depth law was “very hard on some people—a sixteenth of an inch is another 2000 miles.” But they would be dangerous miles, and accidents are harder on people than having to replace tyres when they reach the end of their safe life. In fact, the comments caused by the new regulations show just how necessary the regulations are. Obviously many motorists would continue to drive , on dangerously worn tyres were there no regulations against their doing so. One-sixteenth of an inch is less than the minimum tread depth of 2mm stipulated in several European countries, and tyre experts regard 2mm as the minimum safe tread depth on wet roads. Nobody is likely to deny that cars should, by regulaton, have efficient brakes. Yet many obviously forget that the best brakes in the world are of little use without good tyres. If motorists really want their tyres to last longer, they can make them do so by adjusting their driving habits. Regular attention to wheel alignment and correct tyre pressures and the avoidance of hard braking and fast cornering will greatly reduce tyre wear.