Y25 (25Tn) bogies have been used in freight cars for over 50 years. It is a proven design with a positive opinion in many European countries. In addition to the generally positive opinion about the operational properties of the Y25 bogies, there are sometimes publications whose authors notice certain imperfections related mainly to the so-called running instability, resulting in derailment under certain motion conditions. This paper presents results simulation of motion tests of a freight car with Y25 bogies. A freight car model was created using the VI-Rail software. The research focus on determining the critical velocity and examining nature of the model solutions in the overcritical velocity range. Straight track sa well as curved track motion is analysed. Empty and full wagon properties are considerd. Impact of changes the suspension system selected parameters values on vehicle model solutions stability as well as the vehicl impact on track was analysed.