Originally Posted by Dujo
In terms of preload adjustment affecting actual ride height, there is some minimal effect on ride height by making the springs stiffer before the weight of the car is resting on them, the car won't far as fall since you've effectively increased the spring rate, but it is relatively minimal compared to the actual ride-height adjustment. You really want to set the ride height by determining how far up the lower suspension mount is threaded on to the center threaded strut section.
Preload will absolutely effect ride height, how do you think KW/RCE's work?
Preload does not
have any effect on spring rate. Preload is simply stored energy. A 400lb spring with 1" of preload still has an effective rate of 400lb.