These big trucks are used in some countries to improve freight transportation efficiently. Our task was to analyze and optimize the aerodynamic drag. The nominal speed of the truck was 90 km/h. The necessary simulation was carried out using the software package FlowVision. The customer wanted to reduce the air resistance between the trailers and at the back of the last trailer – the detailed pictures of air flow and numerical values of resistance were identified. With our help, the customer created special spoilers in the space between the trailers and at the back of the last trailer, but we cannot show you these spoilers –we have no rights. It resulted in 4%fuel economy!!!!