Vehicle ride study is normally derived from a 2 degree of freedom (DOF) model with only the consideration of vertical motion. This paper describes a method to build up a model with which the longitudinal motion can be studied regarding the frequency response characteristic. The model for longitudinal response can be separated into two simplified subsystems. The FRFs of each of them are deduced then multiplied to show the full system's FRF. With the non-damped FRF the influencing factors to the longitudinal response can be figured out: Sprung mass, unsprung mass and longitudinal suspension stiffness. Detailed full vehicle model is built up with multi-body simulation method to give deeper study how the components influence the longitudinal shock responses. With the MBS the explicit study on the influence of bushing component is carried out. Firstly the suspension longitudinal stiffness is calculated. Then the modes frequencies was analyzed. Finally the obstacle passing event with the full vehicle model was simulated. By synthesizing the results from the multi-body simulations the bushing component effectiveness to reduce the longitudinal response can be learned. In the end a vehicle experiment of obstacle passing test was launched to give more convincing proof about the bushing component effects.