Under normal conditions, on high friction surfaces such as tarmac or concrete, a single driving axle (front or rear) is more than adequate. The traction potential of the tires generally exceeds the torque applied.However, on low friction surfaces, such as ice, snow or wet roads, and in off-road conditions the traction potential of the wheels can be easily exceeded. In these circumstances the improved traction provided by four-wheel drive is most noticeable.This study concerns the optimization of the recently developed Visco-Lok limited-slip differential and coupling for use in four-wheel drive vehicles. In addition to the traction improvement, the influence on the vehicle handling and stability was investigated.A typical example of a compact SUV, fitted with measuring equipment, was used to assess the Visco-Lok, configured as a “hang-on” coupling, transfer case limited-slip differential and as a rear axle limited-slip differential, compared with conventional slip limiting driveline components. The analysis of the objective test results indicated a substantial advantage in terms of both traction and handling, and thereby vehicle stability and safety, of an optimized four-wheel drive system on low friction surfaces.The adaptability of the Visco-Lok coupling characteristic to the particular application enables the traction and handling performance of this unit in a “hang-on” configuration to be comparable with that of a considerably more complex transfer case system. The Visco-Lok system showed also advantages over an electronically controlled “hang-on” all-wheel drive system especially in vehicle stability and safety.