Abstract
When driving a cnr riith or without a caravan the rollingresistance and the air resistance exist always. 'Ten dri-ving with a caravan it is not alone the aerodynamic pro-porties of the caravan that counts in the energy consump-tion, but also the aerodynamic proporties of the car.The car must be designed in such ajr that the aerody-namical functions are at the front and at the rear side.A spoiler should be redundant.