From the view point of vehicle weight reduction and saving resources, it would be desirable to decrease the steering effort eliminating the assistance of power.
Therefore, we have analyzed the steering effort at low vehicle speeds where steering effort is great, and have introduced a theoretical model based on the contact surface deflection recovering process of rolling tires. This deflection comes from the lateral rigidity and the total deflection of tires.
The following results were obtained from this study. As the vehicle speed increases, the steering effort decreases exponentially. As the steering speed increases or as the vehicle speed decreases, the steering effort increases and the effort approaches the final value which equals the static steering effort.
The static steering effort is not relative to steering speed.
These theoretical results are supported by vehicle experiments.