Four-wheel drive vehicles have recently become widely used for their enhanced safety in a variety of road conditions on the highway and snowy, wet, and gravel-covered roads.

It is well known that four-wheel drive vehicles are superior in maneuverability to two-wheel drive vehicles. We have attempted to explain this superiority by theoretical as well as experimental methods.

This paper deals with the theoretical approach in determining the difference in movements between two-wheel and four-wheel drive vehicles during cornering with varying tire-to-road-surface friction coefficients and wheel loads. Experiments were carried out on paved and snowy roads using the two types of vehicles. As a result, it has been verified quantitatively that the four-wheel drive vehicle provides higher stability with greater variations in friction coefficients and wheel loads, though the difference is only marginal under a steady state.

This paper also reports on the new suspension system developed to implement enhanced characteristic levels of a normal passenger car (vibration, ride comfort, steering stability and control, etc.) without sacrificing the unique features of the four-wheel drive system.