This paper analyses the mechanisms of measured oscillations in the door velocity of a laterally impacted passenger vehicle and discusses their implications for modelling and side impact sled system design. Full-scale vehicle crash tests, barrier and vehicle load-deflection properties, and three finite element simulations are used to evaluate the relative contributions of structural stiffness, elastic recovery, and occupant and seat loading on the response of the door. Characteristic low frequency oscillations are measured in the door velocity during crash tests, but are identified as being the result of occupant and seat loading of the inner door and the resulting deformation rather than vehicle structural effects. It is concluded that the structural stiffness and elastic recovery of the vehicle structure can generate oscillations in the door velocity, but these oscillations are not independent of occupant inertia and thus should not be prescribed to a door in a computational model or component-level sled system.