Fig. 1 and 2 show that suspension system is converted into spring and damper where ms and mu aresprung and unsprung mass respectively. ks, cs, kt are sprung mass stiffness, sprung mass damper and tirestiffness respectively. zs, zu and zr represent displacement of sprung mass, unsprung mass and road respectively.According to Newton’s second law differential equations of motion can be written in standard form as follows: