This topic has been beaten to death. Some people get it, some don't.

Fact is if you have a 1000lb of vehicle weight on a spring, you can preload the spring with spacers (or cranking) up to the 1000lb of preload and the spring behaves the same on compression. The misconception is that the preload gets added to the weight of the vehicle and hence changes the spring rate in some way. In fact, the preload is only a threshold to when the spring will begin to compress and the vehicle weight is always vastly above this threshold.

Here is my theory as to why the ride is stiffer when you crank or space a coil. By doing this you change the angle of the A-arms and suspension components (including swaybar components, axles and steering rods etc.) What makes the ride stiffer is that those components no longer travel in the optimal way that the Toyota engineers meant.

What do I mean by this?
The wheel no longer travels straight up on compression. It might travel outward initially as it goes up and then inward after the arm reaches level. This causes increased friction with the ground and increased angular acceleration (inertia).
The axles travel outward in the tulip and then inward as travel continues. The steering rod changes length because the tie rods don't remain at the same angle. This changes toe angle. The other components and links also operate in less than ideal angles.

This may not sound significant but they all add up to more friction in the suspension. This means more force is transmitted to the chassis instead of being absorbed in the unsprung components. A coil or torsion suspension has very little friction compared to a leaf setup. Therefore slight changes in friction are very readily noticed.

What do you think?

You got it. That's what I meant to say.

Frank.

I was thinking about this too. I figured that in quick jolts the tires would flex and if moving at any speed, the tread would flex enough to let it walk in and out. But.... still something is there that wasn't before... It could very well be this combined with leverage differences make up a noticeable difference?

Frank.

Yes, absolutely this what happens, it's called tire scrub. When I was in the Cal Poly Solar Car Club, I was the front suspension team leader and tire scrub was a concern because it wastes energy. Everytime the suspension moves it eats a little bit of power because of friction between the road and the tire. So we had to design the control arms such that the tire contact point would move laterally as little as possible...all while keeping handling in mind.

Now, I'm not sure how much this contributes to the stiff ride of a lifted truck, but I'm sure it all adds up.

Ok, the bike shocks are different in one way.
They have a preload ring, that when you turn it, puts more force on the spring. This makes it stiffer.
On the 4runner, all it is doing (the coil spacer) is lifting the springs up. It does not put more force between them. On bike shocks there is a finite # the spring can compress/extend, the preload ring is holding it together.
You cannot compare a bike shock to coil springs. What you CAN compare it to is coilover shocks like the ones on the fjz80 (sp?).. like fox makes where the spring stops extending at a certain point. even if you put a spacer on the spring, it does nothing, unlike the 4runner.

Nope, the "preload" ring does exactly the same thing as a spacer. The spring doesn't know the difference between a spacer and the ring. Remember, when you adjust your preload ring you are not on your bike so it just SEEMS like you're compressing the spring more. When you get on your bike, you're still floating on the spring. See figure 1 in the article.

<img src="/forums/images/graemlins/rolleyes.gif" alt="" /> Here is a good way to see how it all works. Measure the length of spring, stock, with the weight of the vehicle and rider on the spring. Now insert your spacer or crank your coilover and measure the length of the spring again with the same weight on it. Make sure the suspension is properly settled in both cases. Voi'la, you will see that the spring is the same length. Same spring, same spring length, SAME SPRING RATE!!

The only thing that changes is the position of the spring in relation to the suspension, body and wheel.