The advantages of numerical simulation for study of impacts in general, and in particular for side impacts are already well known. In a previous publication we presented a finite-element numerical simulation of a side impact in which a barrier impacted a vehicle (1). The simulation takes account of the complex deformation, internal vehicle contacts and contacts between the vehicle and the barrier which occur during impact. This model is now applied in a new context. This article covers a series of numerical studies aiming to optimize structural reinforcement for the series-production Renault 19. The project breaks down into two main parts. The first phase is that of validation of the numerical simulation in two extreme cases of vehicle-structure stiffness. Once these results were obtained, the model then allowed for a hierarchical arrangement of reinforcement zones based on criteria of car side intrusion speed.