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The transfer functions between the variables in linear bicycle models of four wheel automobiles, the input to which is steering angle, were examined. The modal response transfer functions between all of the motion outputs, with the exception of front tire slip angle, were found to be independent of front tire cornering stiffness. It is a role unique to rear cornering stiffness to define the above mentioned transfer functions. This concept was also deductively demonstrated. The concept is true in the frequency domain, therefore, it guarantees that the amplitude ratio between two outputs and the phase difference between two outputs depends only on rear cornering stiffness. However, it is necessary to be cautious, when one applies the concept to phenomena in time domain. For example, the difference in 50 % rise time of two output variables is dependent on front tire cornering stiffness.

While there has been an empirical rule telling suspension designers that a slight rearward inclination of the wheel travel locus could improve ride harshness performance, there has not been any quantitative proof on it, to the extent of authors' knowledge. The authors planned to analyze the phenomenon by quantitatively measuring the force transmission via suspension, to find out that the amplitude of longitudinal force transmission to the sprung mass changes significantly depending on the above inclination angle. Further investigation has lead to a conclusion that the force transmission from ground to tire has a sharp directivity. And that the relationship between this direction and the direction of wheel travel is a dominant factor, which decides the magnitude of longitudinal force transmission to the sprung mass. In order to make use of the finding, the optimal wheel center locus inclination in side view has been studied, to minimize the longitudinal force transmission.