Dudes (e.g. Warmonger and JohhnySVT)...when you cut any coil off a spring YOU RAISE ITS RATE. Period. Indisputable. Fact of physics. Progressive or fixed-rate, doesn't matter.
The equation that defines spring rate (not conjecture, not somebody's opinion, spring rate by definition) is:
K = w^4*G/8ND^3
K = Spring rate in pounds per inch
W = Diameter of the spring wire in inches
G = 12,000,000 for steel springs (a constant)
N = Number of active coils (number of coils that are free to move + 1/2 coil)
D = Diameter of the coils measured to the center of the wire, in inches
Notice the relationship between the number of active coils and the spring rate. Play with the math yourselves and see what happens to that equation when you reduce the number of active coils. For instance if you cut off half the active coils the spring rate is doubled.
I hope this scientific fact provides the necessary "logical explanation".
The questions regarding handling then become, as I've said before even in this thread, 1) does that increase in spring rate then make up for the reduction in travel caused by the cut? Many times, no, and the more you cut the more likely you are to have a mismatch. 2) You've lowered the CG, but have you also lowered the Roll Center so much that the CG now has an increased leverage against the Roll Center (yes, it happens) and your spring rate isn't enough to make an actual improvement, and Furthermore, 3) does the increase in rate make up for the wheel's new placement in the suspension's camber curve, which is typically horrible in a strut suspension? In other words, you've lowered the CG, but now you get 2 degrees if body roll in a corner and the camber curve dictates you don't gain 2 degrees of negative camber back as the suspension compresses, for a net loss in camber?
Things get complicated. Quite obviously a mild cut isn't the end of the world in these cars, but now you have the facts as to why cutting springs isn't the easy be-all-end-all suspension improver.
