Both externally and internally, the air plays an important role in the development of a road car, either to improve their external aerodynamics, improving its stability, having a better acclimatization or to get a more efficient cooling of some mechanical parts and engine. Any optimization of drag improves the resultant fuel consumption and reduces CO2 and noise emissions. This project focuses on the aerodynamic study of SEAT LEÓN, the flagship of the company, using numerical calculation programs based on Computational Fluid Dynamics (CFD). The entire project has been developed in the SEAT Technical Centre (CTS) located in Martorell (Barcelona), specifically it has been carried out in the Aerodynamic section of Physics department known as EG-11. The aim of this study is to visualize and understand the behaviour of the air flow through the side of the vehicle, optimizing each of the aerodynamic elements that compose our car. The study focuses on the side of the vehicle even if, as we have expected, secondary elements such as windshields, bumpers, spoilers, etc. will influence on the final result. We can't continue the overview of this project without talking about the aerodynamic drag coefficient (Cx). The multiplication of this dimensionless coefficient and the frontal area of the car allow us to characterize the resultant aerodynamic quality. In order to minimize the undesired resistance drag, all the elements that influence on the side profile of the vehicle have been redesigned with a powerful three dimensional application CatiaV5, always trying to maintain the original design of the Seat León. All the simulations have been carried out by OpenFoam (on Linux platforn) and the meshing of the vehicle has been performed with ANSA pre-processor. Finally, a visualization tool called Ensight has allowed us the study and analysis of the obtained results. If we want to implement any aerodynamic improvement, the cooperation between all the SEAT departments involved in the development of the final geometry of the car will be crucial. Even if we create good aerodynamic improvements, any modification will have to maintain a final compromise between the external design of the car (aesthetics) and the interior (comfort).