<div class="htmlview paragraph">The purpose of this paper is three fold: to serve as a tutorial for engineers new to the field of drivetrain; to function as a reference manual for those who wish to retrieve some information on a topic they have not visited for some time; and to show the direction that four-wheel-drive technology should be taking.</div> <div class="htmlview paragraph">A brief history of four-wheel-drive is followed by some examples showing the broad range of four-wheel-drive vehicles in use today. All components of typical systems are discussed in some detail.</div> <div class="htmlview paragraph">The mechanics, function, purpose, and logic of different types of systems are described, as are their advantages and disadvantages. Handling characteristics and traction capabilities of some different systems are analyzed.</div> <div class="htmlview paragraph">A majority of the vehicles produced today have systems that simply lock all drive axles together when in four-wheel-drive mode. This limits their use to off-road or extremely slippery conditions.</div> <div class="htmlview paragraph">The mind set or focus of four-wheel-drive as merely an off-road or foul weather requirement has kept us from realizing its full potential. Full-time systems can be operated on good pavement to provide better handling, stability, safety, and comfort.</div> <div class="htmlview paragraph">This paper will show that full-time systems should be applied to all classes of four-wheel-drive vehicles. By providing more features, improving mobility, and making better use of the technology, full-time systems offer greater value.</div>