Hans-joachim M. Forster

BIG CARS, TOO, CAN BE LIGHT ON FUEL

Abstract This paper confronts the widely spread global opinion “big car=high fuel consumption, small car=low fuel consumption” with an extensive analysis of fuel consumption with the object of contributing towards the understanding of the actual interrelation between fuel consumption and car concept. In order to make the influencing factors clear two car concepts are compared which differ regarding empty weight and net power by factor 2 and 4 respectively. It is shown that the power required to overcome the driving resistance increases only disproportionally slowly with the size of the car and that in certain driving modes the power requirement for the accessories of a large car reaches the value required to overcome the driving resistance. The still large difference in consumption between big and small cars is due to the fact that the demand for high acceleration reserves in top gear forces running the engine in a range of poor efficiency and that the possibilities of cutting down the driving resistance are not yet being fully utilized. The conflicting aims of running the engine in the range of favourable efficiency on one side and the demand for high acceleration reserves without frequent manual change of gear on the other side can be solved by using automatic transmissions with adequate shifting programmes. It is therefore certain that the future big cars too will have a lower fuel consumption.