A progressive design was common in passenger cars over the years and in jeeps or willys and can consist of low leaf counts of three or four leafs or higher in the nine to twelve leaf counts. The leaf count and thickness of each leaf or gauge of material relates directly to the vehicle it is designed for, its primary use and its size and weight. Progressive designs although not exclusively are designed with the intent to provide more wheel travel as well as a smoother and fluent cycling of the suspension. In a progressive design that utilizes a high leaf count of thin material it  yields a softer more compliant ride both on highways with expansion joints as well as on trails or washboard roads.