are packs of torsional leaf spings linear, as in obey F = -k*x (or rather Torque=-k*theta)?
No they are not. A torsion bar is progressive. Meaning that the next degree of rotation requires much more force than the previous degree of rotation. k is exponential.
No. Solid torsion bars like the ones in our rear suspension are linear:
T = 0.5*theta*G*Pi*r^4/l
Solid torsion bars are DEFINITELY linear, as Duus suggests. Sway-A-Way goes so far as to quote the spring rates for their rear torsion bars. http://www.swayaway.com/TechRoom_VWguides.php
So, Bruce2, you're definitely off that "a torsion bar is progressive", but it still might be the case that packs of torsion leaves (which are not single solid bars obviously) are in fact progressive.
I know for fact that leaf strings used in carriage suspension ARE progressive - but in that case it comes from having many leaves of different lengths. The torsional arrangement might be totally different.
So if torsion leaf packs are like torsion bars, they're linear... if they're like like leaf spring stacks, they might be progressive
I've always thought that the more you preload the springs, the more you preload the bearings and every other place that causes friction. Friction equals stiffness?
I think kdf is on the right track about the friction thing... even though the friction is dampening it might give the feel of a stiffer suspension.
(1) I don't believe it.
(2) If it *is* true, it's a lame solution.
Re 1: The needle bearings in the torsion housing and the ball joints in the arms are *designed* to produce minimal friction under the load of the whole stinking car. The few dozen extra pound of force you could add by preloading would have a tiny effect on friction. If your bearing are SHOT, maybe, but then it's just going to be a creaky sticky mess.
Re 2: If you want more damping, put on stiffer shocks. Shocks are *designed* as dampers, do the job really well, and are available in a wide variety of stiffnesses. If you could overload the bearings so much that you were seeing significantly more friction at the bearings, you'd just be wearing out your bearings and your springs - asking them to do a job they were never intended to do.