DescriptionStability of land vehicle motions consisting of yaw, sideslip, and roll motion of the sprung mass is analyzed in this study. In the first part of the dissertation, a three degrees-of-freedom bicycle model of a land vehicle is developed. The equations of motion are derived by Kane's equations. Eigenvalue analyses are conducted on the linearized model to investigate the influence of the vehicle parameters on the natural frequency and damping properties, which is followed by analysis of the eigenvalue sensitivity to perturbation of each vehicle parameter aiming to quantify the extent parameter perturbation affects the eigenvalues of the vehicle motions at different vehicle speeds. The second part of the dissertation formulates four common driver models which act as controllers of the nonlinear and linearized vehicle models developed in the first part. Stability properties of the linearized vehicle model with different driver models, as well as the variations of the vehicle and driver parameters, are ascertained via eigenvalue analysis. Two existing maneuvers in ISO standards are introduced and the linearized and nonlinear vehicle models' responses to one of the maneuvers are obtained by numerical integration. Observations and comments in regard to the aforementioned eigenvalue analysis are validated by response of the linearized model. It is also observed that there are apparent discrepancies between the nonlinear and linearized models in response characteristics. Stability and bifurcation analyses of the vehicle models with nonlinearities that exist in the internal dynamics of the vehicle, as well as in the tire forces and moments, are investigated in the third part of this dissertation. The linearized vehicle model with nonlinear tire model is considered first and subjected to a variety of steering inputs with different amplitudes and frequencies. Stability of the vehicle motions under such circumstances can be quantitatively determined by computing Floquet multipliers. They also can be qualitatively verified by plotting bifurcation diagrams, steady-state phase portraits, as well as Poincare sections. The frequency and time responses are analyzed for different vehicle speeds and steer types to demonstrate effects of nonlinearities in the tire model. Nonlinearities in the internal dynamics of the vehicle are also investigated for comparison with the nonlinearities in the tire model to determine which factors dominate the motion characteritics.