From the point of view of aerodynamics, the vehicle offers a number of possibilities for optimisation. A thumb rule states that an average reduction of the air resistance by ten percent leads to a drop in the fuel consumption by two to four percent. In reference to the previous slide, an aerodynamically optimised vehicle stands in conflict with a several other boundary conditions which have to be considered. The illustration clarifies the aerodynamically significant positions and the boundary conditions related to them. While the optimisation of the air resistance and the euphoria related to the cw-value played a central role in the 80's, today an optimum overall package is the target. Driving safety and utility are important factors apart from aerodynamics. This way, the aerodynamics can be improved by a highly inclined front windshield, the heating of the cabin however drops. Additionally, the door grips and tail lights should not attract dirt. A sufficient cooling of the brakes and engine is also required. The smallest sheets, edges and joints have an influence on the aerodynamics apart from the design of the chassis, engine and the tire width. More criteria are indicated in the diagram.