Originally Posted by gagliano
Again, my car isn't a DD, but I see your point.
I disagree about the preload statement though. Any time you change the height of the lower spring perch you are changing preload. That's why some manufacturers put the helper springs in there. When you lower the perch to lower ride height, the helper spring keeps tension so the main springs don't come out of their seats when the suspension gets unloaded on those bumpy roads everyone mentioned in this thread.
You aren't changing preload on the main spring if you have a helper spring in there. And preload on the helper spring is irrelevant since it's fully compressed at static ride height anyway. In no way does dual height adjustability make corner balancing the car any easier or more effective.