Computer simulations are currently often utilized tools in vehicle design, diagnostics of vehicle behaviour and evaluation of their characteristics. The vehicle multibody system (MBS) represents a complicated mechanical system especially when flexible bodies are considered, modelled and implemented in the calculation. Multibody system dynamics is based on classical mechanics and its engineering applications range from mechanisms, through means of transport, to biomechanics. Results of multibody system dynamics are most important for an assessment and diagnostics of transport means behaviour even in the development phase. This paper deals with the multibody system dynamic approach and its application in vehicle multibody systems. The first part of this paper focuses on a general approach to the multibody system of vehicles, especially of rail vehicles, and it includes fundamentals of multibody system dynamics. The next part deals with practical use of multibody system software. A multibody system of a passenger car have been modelled using commercial software, we have carried out simulations of a passenger car running on the real track, and subsequently we assessed its ride properties and evaluated its passenger comfort level.