In this paper, a computational fluid dynamics (CFD) study is carried out in an effort to design and optimize the cabin geometry and its various parts for drag reduction that include the side deflectors, the mirrors and the sun visor. For the validation of computational results, an experimental investigation using a 1/5 scale truck model has been carried out in a wind tunnel. The aerodynamic force as well as the surface-pressure point measurements carried out at selected wind speeds. The flow visualizations using smoke and oil were also performed. With the experimental results, the basic characteristics of flow over the cabin geometry (including the flow separation locations) are compared with the CFD results. The both steady and unsteady CFD simulations are performed. The comparison of steady/unsteady results reveals that the time-averaged unsteady flow characteristics are practically the same as the steady calculations for design purposes.