lowering caps. Eureka-moment after 12 years inertia

Your spring is what the weight of the car sits on. It is the bouncy bit. A spring does not absorb an impact (from a bump), it transfers it somewhere else.
The damper (shock absorber) is the part that does, well, what it's called. It is a compressible gas or fluid that is slow to react - so it does exactly that - absorbs shocks. It's also the damper in that it retains control of the spring which just wants to bounce up and down. It 'dampens' the otherwise uncontrolled reaction of the coiled spring.
The damper would just sink down without the spring, so the spring is of course what the cars weight rests on.
Regarding the spring being under compression, there are a few factors. Firstly you want some load on it because you never want the spring to be loose and become unseated. So even at full extension of the damper it should have a little. Also as springs are progressive, i.e. it takes increasingly more force to squeeze the coils together - by having them under some compression you determine at what force the springs start to work (react). The force is the measure of the impact (of pothole or bump) which can be worked out by the physical size variation of whatever the tyre impacts, coupled with car mass and speed. I'm not smart enough to give you that formula though. And also on a road-car there is an element of droop, which is how far the suspension extends downwards (think pothole) which you can see when you jack up a standard car versus jacking up a car on stiff coilovers. Having the spring compressed will determine the rate the spring opens and thereby pushes downwards (spring pushes upwards into the car body/topmount, opposite spring force pushes down the suspension arm/hub, pushing the wheel to the ground) to extend the damper when it needs to, which is to promote a smoother ride. It's essentially "preload".

Yes you can extend a spring perch (or topmount perch) upwards, or indeed move a bottom suspension mount downwards. Or use a different topmount if the spring is mounted on the shock absorber unit (a coil-over type) to differ the position where the spring top coil sits relative the shock. Or modify the suspension mountings to use a different shock absorber if you have one of the right length.

A spring will only ever be compressed by the weight of the body unless to maintain that body at a given height the spring requires to be preloaded.


a 10" 100lb rate spring contained between 10" seats when loaded with a 300lb mass will compress 3" - (assumming a linear rate spring before anyone chimes in)

Now if we only want 2" of compression under load for the same spring seat distance we fit an 11" 100lb rate spring which preloads it 100lb of force
Now when loaded with 300lb it oly compresses 2"

A ten coil 10" spring rated at 100lb is 10 1000lb springs in series - so


10 coils 10" 100lb - with 300 lbs of force = compresses 3" - 7"
7 coils 7" 142lb - with 300 lbs of force = compressed 2" - 5"

As you cut a coil off the spring the rate increases reducing lowering effect accordingly.

You will also note that you have increased the spring rate 40%

This does not take into account any suspension leverage ratios - this is purely the spring compressions - if you apply leverage ratios, lean angles which as well as changing the spring rates may introduce falling or rising rates to the spring during compression it make significant differences to the required calculations.

The correct way to determine a suspension system on a car is to approach it from first principles. Whats are the sprung corner weights and what do you want to achieve in respect of performance and what compromises are you willing to accept to achieve this.

Now if you fit high rate shorter springs

So you get an 9" spring - yay thats going to be much lower - with a 40% increase in rate - Yay much stiffer

9" spring 140lb rate - compression 2" - 7" - long same length and height as the old 10" 100lb spring.

That ISN'T absorption.


THAT is.

Dictionary definition - absorb:
absorb
/əbˈzɔːb,əbˈsɔːb/
verb
verb: absorb; 3rd person present: absorbs; past tense: absorbed; past participle: absorbed; gerund or present participle: absorbing

1.
take in or soak up

To absorb kinetic energy, the damping article must have the ability to reduce or dissipate the impact oscillations.
When you hit a spring with an impact force, it reacts, thus transferring the oscillation.

To use your own example - if you hit a spring with a hammer, it will bounce right back at your face with the same (or close to) power (force) you hit it with. That is the transfer of kinetic energy. There is no absorption. Metal does not compress molecularly when impacted, so it physically does not possess the attributes to be a car damper. Oil or gas does compress however, making it excellent at damping.

Oil compresses - really - FFS

For anyone else who is interested just go have a search and every explanation worth reading will state that the spring absorbs the shocks.

If that were true then we'd have to come up with a different system for our brakes and every other hydraulic system in existence. Which includes our blood....