<div class="htmlview paragraph"><b>M</b>ANY interesting problems in design are presented in the application of four-rear-wheel drive to a six-wheel vehicle. As axle design is intimately related to the rest of the chassis construction, the axle builder is concerned with the type of spring mounting, the method of taking the torque, and the distribution of the load.</div> <div class="htmlview paragraph">The author specifies a number of factors that positively must be taken into account and provided for in any construction that is to prove successful. He then shows by photographs and describes a number of rear-end four-wheel-drive constructions that have been built and put into operation. Attention is confined mainly to consideration of the methods of spring suspension to distribute the weight among the wheels and to provide for vertical movement of the four rear wheels relative to one another, means for maintaining the two rear drive-axles parallel to each other and in alignment with the chassis frame, methods of allowing some torsional movement of the drive axles, and ways of avoiding excessive angularity of propeller-shaft universal-joints.</div> <div class="htmlview paragraph">Several designs are shown that are applicable to conventional four-wheel-truck chassis having two-rear-wheel drive and semi-elliptic springs.</div> <div class="htmlview paragraph">The desirability of placing a differential between the two rear driving-axles is in doubt. Tire mileages have been high on six-wheel vehicles having no such differential, and the incorporation of one in the design presents complications and serious difficulties. Two experimental designs showing alternative ways of distributing the power uniformly among the four wheels are illustrated, but the design and production problems are stated not yet to have been mastered.</div>