The aerodynamics of a vehicle can be strongly improved by the smothening the underside of the floor. The Bernouilli's principle which was mentined earlier is responsible for this. The covering of the underside of the floor however requires a lot of effort and is also disadvantageous from the point of cooling of individual vehicle components. A complete covering of the floor brings a reduction of the cw-value by 0.045. Only then is the rear-end diffuser (upward extension of the rear underfloor) effective. In totality a cw-value reduction of 0.07 is achieved.
The picture shows the components of the underside covers. The air guidance through the floor underside could be improved this way in the latest S-Class. These covers also reduce the cw-value considerably in the BMW 5-series. The underfloor of the Lexus is equipped with air guiding sheets, which are responsible for a turbulence-free flow apart from cooling specific vehicle components.
Apart from the underfloor cover, the wheels and wheel housings also marginally contribute to the air resistance. This is due to the inclined flow around the wheels. The wheels in combination with the housing produce a complex aerodynamic interaction which has not been researched much. A large potential for the improvement of air resistance is expected in this area in the future. The generation of noise in the area of the wheel housing as a result of large, noisy turbulences also represent an additional problem.