Cabin quietness is one of the important factors for product marketability. In particular, the importance of reducing road noise is increasing in recent years. Methods that reduce acoustic sensitivity as well as those that reduce the force transferred from the suspension to the body (the suspension transfer force) are used as means of reducing road noise. Reduction of the compliance of the body suspension mounting points has been widely used as a method of reducing acoustic sensitivity. However, there were cases where even though this method reduced acoustic sensitivity, road noise did not decrease. This mechanism remained unclear. This study focused on the suspension transfer force and analyzed this mechanism of change using the transfer function synthesis method. The results showed that the balance between the body's suspension mounting points, suspension bush, and suspension arm-tip compliance is an important factor influencing the change in suspension transfer force. For example, the suspension transfer force easily increases in the frequency range of 100-300 Hz in the axial direction of the rear lower arm of a multi-link suspension. In this case, the compliance of the body's suspension mounting points and that of the suspension bushes are close to each other and the compliance of the suspension arm-tips is less. To reduce road noise in such cases, effective methods of reducing acoustic sensitivity are countermeasures that do not reduce the compliance of the body's suspension mounting points in order to avoid increasing the suspension transfer force.
