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. Improved damping in yaw velocity had the strongest effect in improving driver rating in handling and stability tests.
We also found differences in drive systems. Four wheel drive was found to improve performance in every road condition. Front wheel drive with traction control was found to improve performance in some conditions but has a small effect on dry roads. We found that traction control improves the performance of average drivers but not trained test drivers. Four wheel drive improved performance of all drivers.