In this study, the effect of support stiffness on the dynamic behaviour of a large industrial rotor is studied using simulation models and experimental test setup having a mechanical apparatus for changing the horizontal support stiffness. Two different simulation models with different levels of complexity were created to simulate the behaviour of the system. Such verified simulation models can be used to predict the critical speeds and minimum vibration operating speed areas. The achievements of this paper could be utilized in the industries using large rotors when operating conditions can be taken into consideration already in rotor system development.