I'm still not sure I'm getting it. Most people want to lower their car a bit so this would effectively mean a reduction in preload during assembly as the spring platform is wound down. Once the weight is on the car any preload is overcome by addition of the car weight
No...this is correct. ( I was right to say "rate " is linear but wrong to have said preload increases )
Lowering the ride height is the same as increasing the static sag...
This is done by removing preload. It isnt correct to say you will sit at the level of compression it started at when it comes to settle ( at rest AKA static sag) but it might.. This is a workaround that gets the car to sit lower under it's own weight- not to be confused with suspension "tuning" per se..!
The real way to change the set up is to install dampers with adjustable length. (This is what Simon was saying when he said they are fixed ) The allows ride height adjustment independently of preload, and independently of stroke ( ie- you have all the available stroke/travel ) So it doesnt change the static sag, or preload, or have consequences to the damping. Travel is also unaffected - Only ride height ( length of the telescope eye to eye) alters.
I m not going to guess at how the dampers work..It wont wont be progressive damping but they will be variable.... I'll bet they arent independent circuits though( rebound & comp ), which means there is crossover- something modern tuning design has either eliminated.Or in the case of bikes, comp in one fork, rebound in the other...The important compromise here to is that changing one side directly affects the other, like it or not...so there's that !
Im not explaining this very well, sorry..
Tim