I think Mike, and please correct me if I'm wrong, that lighter springs, with more preload in sand is a function of the shape and speed of the bumps inherent to sand tracks. I think you will find that the opposite also holds true (heavier springs with less preload) to fast, hardpack tracks with lots of square edged bumps.
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JTT
"Character is like a tree, and reputation is like it's shadow. The shadow is what we think of it, but the tree...the tree is the real thing."
Abe Lincoln