Abstract— This paper aims to study the vibration of a pickup truck when adding the leaf spring and shock absorbers in the rear suspension system under heavy load. The pickup trucks have been widely used for the logistics system because it is convenient to distribute goods and access to limited areas such as downtowns, and narrow roads. For cost reduction, it is necessary to transport heavy goods. Therefore, the car suspension must be modified, and the vibration responses should be considered. This paper used a haft-car dynamic model to simulate the vibration responses under various loads. The numerical results show that the amplitude of vibration for the car body reduces when adding the leaf spring and shock absorbers in the rear suspension system.