A wake region will be produced by truck when it is travelling at their maximum allowance speed which is 56 miles per hour. The wake region can be seen clearly when a truck travelling at a wet road. The wake region has it’s own force which will affecting any vehicle travelling behind or next to the truck. This paper presents a numerical study of the flow field in the aerodynamics of the saloon effecting by the wake region. Simulation will be carried out for different position of the saloon next to the truck. The numerical study will be validated using Ahmed body to determine the mesh and domain size. The velocity will be set at 56 miles per hour and assuming the truck will be travelling alongside the motorway. The rotating region will be used for truck and saloon and the angular velocity will be calculated based on the circumference of its tires. Detailed analysis and result such as CD and CL together with the x-y chart will be presented to provide a better understanding of the effect of truck wake region to the saloon when it is behind or next to the truck.