Effectiveness of base cavity on the drag of a simplified tractor-trailer model is investigated experimentally. Three different configurations of base cavity, which are solid wall, slitted wall, and slotted wall cavity, are tested for the drag and base pressure distribution at the Reynolds number of 4.1*$10^5$ based on the width of the model. It is found that the slotted wall cavity is most effective; a maximum of 11% drag reduction in the zero-yaw case is achieved.
