Abstract
There is a considerable need for a reliable means of determining the effect of gradient on fuel consumption and journey time of road vehicles. In order to decide whether a proposed road improvement, involving the elimination of steep gradients, is to be an economical proposition, some reliable estimate is necessary of fuel and time likely to be saved as a result. The approach used in the paper is of general application, and depends on equating the engine output to the resistance to motion under uniform speed conditions.
It is concluded that, for a light vehicle, a nearly level surface is best from the economy point of view. Fuel consumption for a journey between two points at the same altitude, on roads sloping at one in four, is nearly three times that for the same journey on the level. At the same time, the journey takes over three times as long.
The paper also reveals the inherent inefficiency of the spark-ignition engine used, as it is for the majority of journey times, at part-throttle operation. Arguments are made for wider gear ratios and improved engine characteristics on private cars.
The MS. of this paper was first received at the Institution on 8th November 1951, and in its present form, as accepted by the Council for publication, on 8th March 1952.
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