The object of this paper is to explain the simulation methods of vertical and longitudinal forces applied to a vehicle body running on rough road. First, a background of the demands of rough road load and the present state of simulation methods are described. Then, the simulation method of histogram, which is important for durability procedure, is mentioned. A histogram of vertical force can be simulated from chassis characteristics from running on rough roads. Second, a computer simulation of vertical and longitudinal forces of running vehicle is discussed. The tire is modeled as a radial spring system which is connected to the chassis model and the propriety of this simulation is investigated by comparison with the actual test results. In conclusion, through the above-mentioned research and development, vertical and longitudinal force can be simulated for rough road running.