A fork's actions are affected by three forces: friction, spring resistance, and damping. Since most people don't toss around the big bucks that factory race teams use to put low-friction coatings on fork sliders, the static friction between the stanchion (inner fork tube) and slider remains constant and is not affected by other suspension changes. Springs, one of the most common modifications people make, know only one thing: Position, how much the spring is compressed. The more compression, the more pressure the spring pushes back with. If a bike wallows or bottoms frequently, increasing the spring's preload (i.e. increasing the spring's initial pressure) or putting a heavier spring in your fork will result in a firmer ride, possibly eliminating the problems. However, since the spring's increased pressure acts on all bumps, whether their shape and size require the increased pressure or not, the firmer ride may suffer from excessive stiffness. Variable-rate springs attempt to remedy this problem with a softer spring rate in their initial travel and more resistance as they compress. Thede feels progressively wound springs address the problem in a backwards way. The spring becomes its stiffest when he believes you need the most flexibility -- absorbing large bumps.