There are a number of other points which should be borne in mind by auto owners with the coming of hot weather, if the most efficient service is to be had from the car.
One of the Y. M. C. A. secretaries excitedly called the school to ask why a seemingly good tire should blow out after a short run. A few minutes later another secretary put the same inquiry with variations. That is, he had a tire which was rather old, but it had been inflated for two weeks and had been running every day since inflation, when it tested eighty pounds’ pressure. It had blown out.
The first secretary had been invited by a friend to take a ride. He had watched the tires inflated and all other bits of preparedness and saw that nothing was overlooked, and settled down for a fine ride. The blow-out came about five miles away.
The trouble with both was that they had not taken into account the fact that summer was at hand. Experienced drivers know that in hot weather, whether it is according to rules or not, it is better not to keep the tire pressure so high as during the cold months, even though it means more wear on the tires.
Considerable heat is generated by rolling a tire over the ground. This heat expands the air in the tire and increases the pressure. In the winter this heat is absorbed to a large extent by the cold atmosphere and the cold and wet pavements, and therefore the pressure does not vary so much. In the summer the roads are very hot, the air temperature is high, and the heat generated by friction is not carried off to any appreciable extent.
On a recent summer trip the writer noticed that the car was riding harder than usual and a test of the pressure on the tires developed the fact that it was above normal. To find out just what the difference in pressure would be, the pressure for each tire was taken before leaving the garage next morning. After rolling about forty miles at an average speed of thirty miles an hour, the pressure was again tested. It had increased about twelve pounds on each tire.
Several tire manufacturers insist that owners shall not carry less pressure on tires in hot weather, saying that the increased pressure due to heat is not sufficient to materially affect their make. This probably is true for new tires, or for about two-thirds of their guaranteed life, but if the tire has been weakened, through having been run under-inflated, or from fabric deterioration through cuts in the tread, there is danger from the increase in pressure due to heat.
More tires are damaged by under-inflation than by over-inflation, because the former breaks down the side walls through running flat, in practically every case, while the over-inflation causes a blow-out only when the tire is weak at some point. It would be good practice, however, on hot summer days, to leave the garage with the tire pressure about ten pounds less than that specified by the manufacturer as being correct for his make. Any driver ought to test out his tires after running at a good clip on a hot day and find out just what they do. A little persistence would enable him to understand how much his tires heat up and he could regulate the pressure accordingly.
Manufacturers of high-pressure tires resent the above advice and declare that it is wrong. The succeeding chapter tells of definite tests made and the owner can draw his own inferences and decide for himself whether he wants high tire mileage, or comfort with pretty good tire mileage.
There are some other hot-weather points which it might be well to keep in mind if one would get the best results from the car. One of these is the care of the carburetor. It will be found usually that not quite so much gasoline is required as in cold weather, and therefore the dash adjustment may be carried a little nearer the lean, or air, side. This not only saves gasoline, but increases the power of the motor, for a too heavy mixture makes it run logy.