Tyre Tread Standards

Press, Volume CVIII, Issue 31784, 14 September 1968, Page 12

Tyre Tread Standards

Fewer than 4 per cent of road accidents causing injury or death are attributed primarily to mechanical faults of vehicles. Credit for the apparently minor importance of mechanical failures as a primary cause of accidents must be shared by manufacturers, by motor mechanics, and by motorists who, for the most part, are keenly and sometimes fastidiously interested in the mechanical welfare of their vehicles. It is all the more regrettable that many drivers are less interested in the way they handle their vehicles on the roads. The checks for warrants of fitness obviously play no small part in keeping vehicles up to scratch The proposal by the Minister of Transport, Mr Gordon, to include in the examination for warrants new checks on the body structure and tyres of vehicles is good as far as it goes. Although it may draw attention to the need for sound tyres, the proposed standard for tyre treads does not go very far. No motorist should assume that the minimum thickness of .3 millimetres of tread on a tyre assures him of safe driving. The Traffic Regulations now prohibit the use of tyres that have “worn or “ damaged cords apparent by external examination ”. A tyre on which the cords are “ apparent ”, let alone worn or damaged, has passed so far beyond a reasonable standard of safety that the regulation must be regarded as a mere stopgap among the law’s minimum standards for vehicle fitness.

A depth of tread of .3 millimetres is barely measureable. It means no more than that the pattern of tread is discernible on the tyre. It is certainly no guarantee of safety in driving on wet roads; tyre experts consider that a tread of at least two millimetres (about a twelfth of an inch) is required to break up the film of water on the road sufficiently to give adequate grip for steering and braking. Several Continental countries demand this minimum. The British regulations, which came into force this year, require a minimum thickness of tread pattern of one millimetre. The wise motorist will replace tyres long before they reach this stage. The proposed legal minimum for tyres in New Zealand—at the time of inspection for warrants—would not make the regulation on tyres much more than a last-ditch stand against dangerous negligence. Many accidents not primarily caused by vehicle faults might be avoided, or rendered less serious, were such critical equipment as tyres kept at a higher standard of efficiency.