FITTING OF NEW TYRES

Press, Volume LXXII, Issue 21760, 17 April 1936, Page 20

FITTING OF NEW TYRES

autumn or early winter BEST TIMES RUBBER AS CONDUCTOR OP HEAT It has long been established that tyres wear more quickly in tHe summer than in the winter. In summer the road surfaces are hot and air temperatures also are high, and, in addition, the work done by the tyre produces heat. It happens that rubber is a very poor conductor of heat, and cooling during the summer months can only take place at a very slow rate, whereas in winter the situation is very different, for the roads are cold and are often covered with water, while the temperature of the air is nearer freezing point, so that the tyre is able to cool considerably and the temperature of the rubber is kept down. Some tests were recently made in an endeavour to determine exactly the effect of these different conditions, special care being taken to eliminate all variable factors. Precise records were kept of sunshine and rainfall. In the first period there were 16 hours of sunshine per 1000 miles covered, and the rainfall was 2 mm. In the second period there were only three and a half hours’ sunshine per 1000 miles, while the rainfall was 24£ mm., or lin. It was found that during the hot period the rate of wear was approximately two and a half times that during the colder and wetter period. In considering these figures it must be remembered that during the summer dust and fine road grit are usually to be found on the road surface and have a very definite abrasive action. Experience suggests that, taking these factors into consideration, the rate of wear during the six months, including the summer period, is approximately 50 per cent, greater than in the other half of the year. This raises an interesting question. At what time of the year is it best to fit new tyres? In considering this it must be realised that wear is partly brought about by the distortion of the rubber forming the tread. Now the deeper the tread pattern—that is, the deeper the isolated blocks and ribs which form the tread pattern—the greater will be the relative movement under load. This explains why, when rates of tread wear are carefully measured, it is always found that m the early stages, while the tyre is new, wear takes place somewhat faster than when, for example, the tyre is half worn, and that there is a gradual diminution in the rate of wear as the life increases.

It is, therefore, only logical to fit new tyres at a time when the forces causing wear are at a minimum. A new tyre with a deep, bold tread is less able to resist wear in the summer than it is, in the winter, and the autumn and early winter are the best periods for fitting new tyres. If this is done the new tyres run on cool, wet roads, so that while they are most susceptible to wear they have the conditions most favourable for avoiding wear, and when the summer arrives and produces the conditions most favourable for wear the tyres are in a better condition to resist it. TWO TAIL-LIGHTS arguments for and AGAINST A discussion is raging at present in England on the advantage, or otherwise, of twin tail-lights on cars. One o'f the points made in favour of the twin lights is that they allow a driver of a following car to judge the distance between him and the car in front. Another claim put forward is that the width of the car can be judged immediately. In reply to these statements a correspondent of the “Motor ’ asks what value this information could be. He mentions that in overtaking another car at night the faster-moving car generally comes up fairly carefully and at a moderate speed, and long before it is close enough to pass the entire width of the leading car could be seen. The writer also states that should the off-side rear light fail, the fact that the other was burning would not mean immunity from a summons. The regulations state that the rear light has to be placed either on the centre line of the car or to the off-side. If the off-side lamp does fail, the burning of the near-side light might constitute a danger.