Ok, I'm gonna do this again but more basic....

Did you ever take Algebra? Do you remember the equation of a line Y=MX+B? It just happens that the spring rate number is the "M" or slope in that equation. Spring force F=KX, K being "M", the spring rate constant. Now pay close attention to the words you are using especially the word, "rate". The spring force increases with a LINEAR RATE. This means two things. First, it is true that to hold that bow stretched at a farther distance requires more force. (The X value is larger) Second, and very importantly, if takes X amount of force to stretch it say 1", it still takes that SAME amountof force to stretch it another inch even when it is pulled taught.

Your example of the motorcycle shock may or may not apply. For example, when it is in the bike, is the shock still maxed out? This is very important if you are to try to draw a parallel. If it is maxed, is is similar to taking torsion bar and adjusting it until at rest, the suspension is fully extended, then adjusting more. You are simulating more weight by smashing the bar against the bumpstops. We typically don't do this to our trucks so it would not apply. However, if the motorcycle shock is not fully extended (it isn't, I have one too, if it were you eat crap on corners when the tire leaves the ground because it can't extend into pavement depressions) then the shock will behave similar to our trucks. You move the adjustment point so that if say you add a heavy rider, the bike returns to a proper ride height as opposed to sagging. The extra load is from the RIDER!!!!!!!!!!!!

Anyway, all of this theory was the result of real world testing and has been proven millions of times and is at work in your truck, bike, scale, bow.. whatever as we speak.

Your leaf spring analogy is really applicable. The arching of the spring in fact strain hardens the metal, among other things, increasing the spring rate. You could do that to any spring if you wanted.

Springs are springs because they return to their original shape. Bubble gum deforms but it ain't too springy is it? Solder resists deformation but it isn't too springy either. Harden steels can resist deformation like crazy but when pushed too hard break instead, not very springy. Spring steel resists deformation but, as long as you don't exceed the yield strength, returns to it's original shape thus making it a spring.

And lastly... this is to explain WHY the torsion bar suspension feels stiffer when the angle inceases (it's not because of the spring, it's the difference in torque)!!!!! Not to say that it doesn't.!!!

Frank.