The chief factors affecting the riding quality of a motor vehicle are spring deflection, or amplitude; periodicity, or the number of vibrations per second; and the proportion of the sprung to the unsprung weight. Other factors are the wheelbase, the tread, the height of the center of gravity of the car and the effect of the front springs on the rear ones. The three main factors are considered at some length, various experiments being described and illustrated by diagrams. Spring inertia and the fundamentals of periodicity are then investigated, by experiments and mathematical analyses, in considerable detail. Experiments regarding possible future spring construction are described and discussed and the advantages offered by the suggested suspension are stated as sensitiveness at light loads; a minimum flexure for a maximum of axle motion; sensitiveness at all loads against quick upward thrusts of the axle; reduced weight of the unsprung mass; larger deflections at light loads and proportionately small deflections near the maximum load; and a saving in spring weight.