This paper studied the transient flow-field response of a simplified vehicle pitching around its front axle. The transient numerical solver employed is based on the large-eddy simulation. The sinusoidal -pitching motion was imposed on the model, and the Strouhal number was 0.13. The numerical method was validated with wind-tunnel experiments. The change rule of the results between transient simulation and quasi-steady simulation is quite large. It has been found that the quasi-steady simulation cannot reproduce the aerodynamics performance of vehicle driving on road. It has also been found that, from the transient simulation results, there is a time lag at the extreme position, which suggests that the flow-field has hysteresis effects. The complex flow-field of transient flow around the road vehicle was thoroughly understood from the space and time through the Q-criterion to identify the coherent structures of the flow.