Join Date: Jul 2007
Location: Collinsville IL (by St Louis)
A more important question is WHY do you want a progressive rated spring? Progressive rated springs have their place (even on sport bikes) but are generally used in very specific situations and for very specific results. Any progressive rated spring can be hard to tune and will feel different in parts of the stroke. This can cause things like pump or wallow in the initial part of the stroke and then be possibly too stiff as the suspension moves further into the travel. Progressives can also make setting up damping difficult too.
As to the rate, they make a wide variety of rates, so it would be stamped on the spring what the rate starts at and then what it ends at.
If you're like the idea of a progressive rate spring, using a combination rate, preload and topout springs can imitate the same affect as a progressive rate spring without compromising other key parts of the bike's handling.