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Torsion beam suspensions are lightweight and low in cost, and they are therefore frequently used as the rear suspensions of small front-wheel drive vehicles. However, it is difficult to predict their characteristics and to satisfy performance targets in the early stages of development in particular, because the various aspects of performance required of a suspension must be achieved by a single structure. A great deal of research has been conducted into the cross-sectional shape of the beam section; however, this paper focuses on the effect of the properties of the trailing arms on suspension characteristics. Two similar test torsion beam suspensions differing only in the rigidity of the trailing arms were fabricated, and kinematics and compliance (K&C) tests were conducted using a 3D measurement system. The lateral compliance test showed the anticipated result that change in toe and camber is greater in the suspension with lower rigidity trailing arms.

The dynamic performance of a vehicle traveling at high speeds is affected by the aerodynamic characteristics consisting of lift on front and rear axles, side force, and yawing moment. In order to enable consideration of these aerodynamic characteristics from the early stages of the vehicle development process, it is required that the characteristics are replaced by simple development indices. The study discussed in this paper introduced the concept of equivalent cornering stiffness to analyze these aerodynamic characteristics from the viewpoint of vehicle dynamics. Using this method, it is possible to integrate four aerodynamic characteristics into two variables which are very important to vehicle dynamics. As a result, the interaction between each aerodynamic characteristic is simply expressed in the equations of motion. Moreover the aerodynamic characteristics are dealt with as the same variables which are commonly used in other chassis systems such as suspensions and tires.