Figure 3: Definition of generalized coordinates and geometry properties.Figure 4: Parameters for stiffness and damping.The potential energy stored in the spring is given by where and are the displacements and stiffnesses of the front eye bushing.denote the lateral and radial displacement of the shackle with as the corresponding stiffnesses.A non linear bushing description including a linear and a cubic stiffness gives the forcesand the potential energywhich can be used in equation (2) instead of the linear model. The forces will in this case depend on