which is stiffer? if you have a 400 progressive spring, whats the equivalent of that in linear? would it be stiffer?

 

Progressive springs dont have a rate and there isn't an easy way to calculate their equivalent in linear. One isn't stiffer than the other simply by which type they are, but by the stiffness of the coil itself. It's also possible that a linear rate spring would be stiffer than a progressive under light load, but softer than the progressive spring is when it is under heavy load.

Progressive means that the rate stiffens as you apply more load to the spring. Its a street compromise, so that for most bumps you have a fairly soft rate, but when you corner hard you don't body roll too much. Nearly all aftermarket springs and coilovers are progressive. Racers prefer linear rates because they are more predictable.

You can easily identify them by looking at them. Linear will have even spaces between the coils for the whole spring. Progressive will have small gaps at the top of the spring between the coils, increasingly larger gaps until somewhere near the middle, then the gaps will get smaller again at the bottom of the spring.