Fair enough.

 

I thought about this one and here's why. Let's go back to your example: If a spring with a rate of 500 lbs. per inch is compressed 2 inches by movement of the suspension, the force required was 1,000 lbs, and 1,000 lbs. of force will be released when the spring rebounds and must be controlled by the damper (shock). A spring with a rate of 650 lbs. per inch, on the other hand, would only be compressed about 1.54" by the same 1,000 lbs. of force. It will also release the same 1,000 lbs. of force on rebound, and therefore require the same amount of damping.

It's true that the same amount of energy is stored and released by the springs in the above example. In the above example the 500 pound spring is compressed 2 inches and the 650 pound spring compressed 1.54 inches when the same 1000 pound force is input. In both cases the same amount of force must be dissipated, but in the case of the firmer spring there is less displacement available over which to dissipate this force before the spring is fully extended again.

Dampers are velocity sensitive. The faster you move a shaft in a damper the more resistance the damper will provide to the displacement of the shaft; the inverse is also true. Velocity is measured as distance traveled per unit of time.

Let's put the same damper on both springs. The 500 pound spring is compressed 2 inches by the 1000 pound force. That means as the spring uncoils the damper has 2 inches of displacement available to dissipate the force while the 650 pound spring only has 1.54 inches of displacement available. If time is constant in both cases the 650 pound spring can return the car back to ride height by only traveling 1.54 inches while the 500 pounder must travel 2 inches to return to ride height. Since time is constant and the 650 spring has a shorter distance to travel in order to reach ride height once again its shaft velocity will be less than the 500 pound spring.

The same amount of energy must be dissipated in both cases but the 650 pound spring will dissipate that energy at a slower shaft velocity than the 500 pound spring. Since shocks are velocity sensitive moving the shock more slowly results in less damping. Since the shaft velocity is lower with the stiffer spring we need more damping force within the damper than we do for the softer spring.

Therefore higher rate springs require higher rates of damping.

 

Excellent point. You win.

 

I was wondering when you were going to get to that. What did you win

 

For poor ProjectRxSeven, who got this started, I've got a feeling he's way lost!

Understanding suspension requires a fairly sophisticated understanding of geometry and physics - which is why engineers do this stuff. For us non-engineers, there are some good sources of information to help us understand the qualitative concepts - just don't ask us to work the differential equations to come up with the actual numbers. The gold standard, as far as I am concerned, for explaining suspension to the non-engineer types is Fred Puhn's "How To Make Your Car Handle" - it's getting a little long in the tooth at this point, but it keeps getting reprinted because it is so helpful, and geometry hasn't changed that much. It's $14 at Amazon.com. Worth every penny if you want to understand what your car is doing and what effects modifications will have.

 

mac and everyone,

This is pretty helpful. I'll admit i need to sit down and break down the information posted here and i'll probably go out and buy that book you suggested, or borrow it. However, I don't think i'm going to give up on understanding the technical end of things, just yet - the physics and geometry and so on. It would just be cool to really cool to figure it out. Even if it takes a while. That way it would be easier in the future. Plus, I think that when it comes down to it the mathamatics/ formula's and concepts or laws of physics are relatively basic. It's just visualizing and anticipating or trying to apply these things to physical experience. Too much info isn't always bad. But it's good to start easy, so I'll try and get my hands on that book.

peace,


Mo

 

The satisfaction of knowing he belongs to an incredibly small group of people on this forum who can actually produce a logical and accurate explanation supporting their beliefs when questioned...

 

Jim, Thats a prize worth winning. Maybe someday you and I will be able to do that.

 

Maybe not. I'm the one who determines who belongs to that rarified group.

 

HAHAHA! Always the last word!

 

That sounds like an old Woody Allen joke. "I would never want to join a club that would accept me as a member"