Quote:
Originally Posted by SD1too
I see that you are a professional engineer Ken so can you help me with this please?
Whenever I fit a shock absorber I have to raise the car body very high, beyond spring-determined height, in order to insert them. When the body is subsequently lowered the spring partially compresses but so does the shock absorber. A point of equilibrium appears to be reached. Surely this would depend upon the ability of both the spring and the pressurised shock absorber to compress, wouldn't it?
If I removed my shock absorbers completely, would you say that the car's body height would be identical to that with the spring/shock absorber combination fitted?
I'd be grateful if you could explain where I am going wrong with this.
Simon
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Try a static damping test: Stand beside one corner of your car, push it down hard & then let go. When the spring pushes the body back up it overshoots the normal (rest) position then drops back to it. This is correct damping.
Explanation
When a car is sitting in its normal position (rest), the suspension must be partly compressed. (Typically by 1/3 of its travel as I understand it.) This is so that the body can move both down and up relative to rest when it goes over bumps.
A) If the damper were at its longest position when the car was at rest, when depressed it would go down, rebound to the rest position, then hit the top of the damper and break it.
B) If the damper were at its shortest position when the car was at rest, when you pushed down it would not move as it would be acting as a solid rod, giving a very uncomfortable ride.
An Aside
Drag racing cars often have rigid or very stiff dampers so that they don't compress when starting off so that the weight on the wheels, and hence the grip, is better.
I hope that helps.