The optimisation of the cw-value can be achieved first by the improvement of detailing. Apart from the basic aerodynamic form of the vehicle, numerous details have also to be tuned from the point of view of aerodynamics. The modification of details such as the radii of edges, curvature, pull-ins, the position and geometry of spoilers can have a large influence on aerodynamics. These measures hardly affect the pre-defined design.
The design of the A-pillar can be used as an example. By rounding off the A-pillar, the resistance to air-flow can be reduced. In addition, demands for a water and noise-free design should be taken into consideration. To prevent soiling the side window pane as a result of the flow of water from the windshield, the A-pillar has to be accordingly designed. The design of the water guiding sheet (gutter) on the A-pillar are to be considered critical from the point of view of aerodynamics. The picture on the left shows a modern strip integrated into the A-pillar. A groove with a relatively small cross-section is sufficient. Water guiding grooves in the driving direction and hence in the direction of air flow, such as between the door and roof are not critical from the point of view of aerodynamics.
The same problem arises in the region of the rear window (picture on the right). In order to prevent rain water from flowing back, small grooves are introduced. A compromise has to be made in the size and form of the grooves, in order on the one hand to guide water and on the other hand not to influence the aerodynamics.