To limit the threat posed by global climate change it is vital to reduce the emissions of the transport sector in the short term. Two existing aerodynamic add-on devices for the rear-end of a heavy duty vehicle, a tail and guide vanes, are combined in an attempt to achieve a larger drag reduction. A research is performed using numerical simulations and a wind tunnel experiment in the Open Jet Facility to gain insight in the interaction between the tail and the guide vane. It was found that the guide vane is able to further increase the base pressure of the vehicle, but that the drag reduction is sensitive to the drag of the vane. Due to the interaction between the tail and the guide vane the largest drag reduction is achieved when the guide vane is operating at its minimum drag condition.