<div class="htmlview paragraph">Riding-comfort is defined as the transportation of an automobile passenger in so easy a manner that the trip will be a pleasure and not a hardship. Since spring-suspension constitutes the basis of riding comfort in passenger-cars, the paper deals with some of the important factors that determine correct chassis spring-suspension. An analysis made by the National Automobile Chamber of Commerce of replies received to a questionnaire it circulated among 20,000 car-owners is presented in proof of the genuine interest the motoring public has in the riding-quality of a car and the variable factors that have an influence on spring-suspension are stated to be the type of spring used, its physical dimensions, the amounts of sprung and unsprung weight, frame construction, wheelbase dimension and the kind of material used.</div> <div class="htmlview paragraph">Horizontal, vertical and sidewise motions of a car are analyzed, and a periodicity chart is shown for passenger cars of from 112 to 116-in. wheelbase. Since periodicity is a function of deflection, the derivation of the number of vibrations per minute is explained and the reduction of vertical motion is discussed.</div> <div class="htmlview paragraph">A periodicity machine designed to determine the value of interleaf friction as a damping medium is illustrated and described, and the results obtained from tests are stated. Sidewise motion and the effects of balloon tires and four-wheel brakes on riding-quality are treated briefly.</div>