Tire Wear and Fuel Consumption

Abstract

In order to survey the economics for a given country of driving with cold GR-S and natural-rubber tires, we proceeded as follows. With the usual average life of a tire as a starting point, the difference in life was calculated for the two types of rubber on the basis of relative wear resistance measurements. Based on the price of the tire this difference at each temperature is expressed in terms of money. There is obtained in this way, therefore, for the country selected, a curve showing price difference vs. temperature. This curve has to be further corrected because of the greater fuel consumption when the driving is done with cold GR-S tires. Even with equal tire life, it is certainly an advantage to save some fuel. Since our observations on fuel consumption showed no dependence on temperature, this correction only produces a parallel displacement of the curve of price difference vs. temperature. As an example, the resulting curve for West Germany is given in Figure 7 (lower diagram). With the aid of this curve every car driver in West Germany can calculate for himself what is the advantage or disadvantage of natural-rubber tires. For this he needs only to know how many kilometers he has gone at the different temperatures. The upper half of Figure 7 gives a view of the distribution of kilometer performance (mileage) of all private cars in West Germany. The percentage of the tire mileage at the different temperatures is given. In deriving these results, use was made of some statistical data on the traffic density in different months of the year. These data were from the Central Bureau voor de Statistiek in the Hague. Also the meteorological mean temperature values for definite hours of the day and months of the year were taken into account. The conclusion for West Germany is that, on the average, there is a distinct advantage in driving with natural-rubber tires. Conclusions for other countries can be drawn in a similar manner. They are given in very brief form in Figure 8. Surprisingly enough Figure 8 shows that GR-S is advantageous only in a very warm, i.e., tropical, climate. In all other countries, natural rubber shows more or less advantage. An estimate by J. C. Gerritsen, to whom we also are indebted for most of the preceding calculations, shows that over 70 per cent of the motor vehicles in the world can run more economically on natural-rubber tires.