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Engineers understand the advantages of four wheel drive on low coefficient of friction surfaces. The advantages of four wheel drive for other surfaces and for handling and stability are not well documented. When surveyed, customers tell us that four wheel drive feels safer for every road condition including dry road. The object of this paper is to determine what factors contribute to the driver's feeling of safety and how different drive systems affect driver confidence. We tested three different drive systems; front wheel drive, front wheel drive with traction control, and four wheel drive. Acceleration, steering angle, and yaw velocity were measured for these vehicles on a wide variety of road surfaces. Subjective ratings of stability were made by professional test drivers and average drivers. Acceleration and handling tests on various surfaces were also measured. A correlation was found between driver ratings and measured parameters.

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.