Dynamic load is a two-way impact factor that impacts both the vehicle and the road, potentially causing damage. During the movement, the dynamic load generated by the means of transport has a significant impact on the axle/road and the vehicle’s dynamic safety. This paper studies the effect of tire stiffness on dynamic loads on multi-purpose forest firefighting vehicles. The author separates the structure of the multi-body system, applies the Newton–Euler equation to establish a dynamic model, and uses Matlab Simulink software to investigate and determine the dynamic load acting on the vehicle from the road surface.