Fork Springs :
Progressive/Dual rate Springs : Although not strictly the same thing, they shall be grouped together here. The spring’s rate of change is ‘position sensitive’, and this type of spring is more suited to commuting and touring; allowing a plush initial ride with ‘firming up’ in reserve for those unexpected pot-holes. However due to the affect these types of spring tend to have on damping, they are not so suitable for more spirited riding!!
Linear or Straight Springs : Exactly as it sounds, the rate of change is constant all the way through the spring – 1N for the first mm will mean 2mms compression requires 2N, simple! But there are exceptions, one of which is simply the spring maker putting a minute taper at one end; and the other is when the spring is being affected by another (see digressive).
Digressive/Regressive Springs : Zenodamper in association with fellow moderators on The Independent Bike Suspension Forum (IBSF) has done much background practical on these theories; utilizing ideas that originated once upon a time solely within top of the range racing fork, and adapting the concept to work very successfully within all types of fork. This concept can be added so as to modernize your current fork, or in the case of some designs be reduced or removed so as to bring about a more recogniseable or traditional feel to the bike.