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A kinematic analysis method that determines roll center of a planar half-car kinematic model with variable tread width is proposed. For this, a half-car model whose wheels are assumed to be connected to the ground by revolute and prismatic joints are constructed, and instantaneous centers of the wheels with respect to the ground of the model is estimated by poles of the wheels with respect to the ground for small roll displacement. Then, the theorem of three centers is applied to determine the locus of roll center of the half-car model. Using the proposed analysis method, roll displacement of vehicle body, wheel angle variation, wheel contact point variation, and centrodes of relative motion between vehicle body and the ground, which is the locus of roll center, can be calculated.

In rallies, it is required to develop the high stiffness and high strength suspension parts in order to maximize the handling performance and reliability to severe race condition. To determine which part we should focus on among the suspension parts in the development stage, it is required to consider the driving condition and the various rally road conditions. First, it is necessary to increase the lateral stiffness and camber stiffness of suspension systems in order to maximize the handling and cornering performance. As the result of finite element (FE) analysis for production car suspension, it is verified that the stiffness of axle assembly affects mainly on the lateral stiffness of suspension system. Second, the shock loads under severe conditions such as landing after jump and bumpy road and the driving and braking torque are concentrated on the axle assembly. As the result of above consideration, developing the high stiffness and high strength axle has been considered as the most important work for the project of rally car suspension development. For the development of new prototype car, hub and upright have been newly developed and new big bore wheel bearing has been selected in order to increase the stiffness of axle assembly. Newly developed suspension components have been installed in the new prototype car and 3 different test cars have been introduced to verify the effect of high stiffness axle. Finally, Kinematic and Compliance (K&C) test result for these 3 test cars shows that the stiffness of axle assembly is the most significant parameter to increase the lateral stiffness of whole suspension system.

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