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In this paper, the effect of passengers on the chaotic vibrations of the full vehicle model is investigated. The vehicle system is modeled as a full nonlinear seven-degrees of freedom with an aditional one -degree of freedom for each passenger. Four passengers are added sequentially to the vehicle that produces eight, nine, ten and eleven degrees of freedom models, respectively. The effect of passengers on the chaotic vibrations of vehicle is studied for the above mentioned cases. The nonlinearities of the system is due to the nonlinear springs and dampers that are used in the suspension and tires. Roughness of the road surface is considered as sinusoidal waveforms with time delay for tires. The governing differential equations are extracted by Newton-Euler laws and are solved numerically via forth-order Runge-Kutta method. The analysis is conducted first by detecting the unstable regions of the system and then followed by a specific excitation frequency, where there is possibility of chaos. The dynamic behavior of the system is investigated by special nonlinear techniques such as bifurcation diagram, power spectrum, pioncare section and maximum lyapunov exponents. The obtained results represents different types of nonlinear dynamic absorbers in the vehicle with and without passengers. Consideration the passengers and increasing the mass of the system can resultes in a significant changes in the dynamic behavior where improves the chaotic vibration of the vehicle.