C Spanner

[brainbug007]

Nice one, thanks alot for the help ozzy

[Wynand]

Im gonna be devil's advocate...

Bottom perch/adjuster nut type coilovers: correct me if Im wrong, if the spring is fitted to the shock and the slack taken up by the adjuster nut, the shock will be fully extended. Iow, if a spring is anchored and tensioned it will have an opposite force, meaning it will extent the shock fully.
That said, by further pretension of the spring the spring will get shorter but the same principle remain and the spring will still push the shock to its fully extended length. How can the car lowers itself when the spring is tensioned?

I can understand that if the car sits to low and the bound/ rebound position on the shock also to low/little, pretension can get the car higher because coil springs used are linear example; 1" = 200lbs, 2" = 400lbs etc - Because pre-load doesn't increase spring rate at all, all it does is add a force that has to be overcome before the spring takes action It seems pre-load is a nasty thing...

And this begs my question, how would the adjusting of the spring (compressing/releasing) raise or lowers a car

EDIT: I was lucky with my spring rate - the car squat down to the designed ride height and the springs feels nicely weighted and act immediately when putting further weight on them. But I sat for quite awhile looking at the front to see if I tension it, there would be a difference but fail to. Not keen adjusting them under load of the car to see if it will. Btw, I only pretension my springs by hand, about half and inch before installation

I think the art is rather to have the springs calculated correctly that when the car is loaded on them, it sit on its desired height.

[robo]

Because the spring/shock combo if correct in poundage would not be in the topped out position once the car was on the floor. Thats when the adjusters take over to trim ride height.

Bob

[baz-r]

i think people get a little confused with suspension setup i have worked on meny modified street cars that handle horrably it all to easy to over do it
we just need to brake it all down to the basics realy

a spring holds the body up winding up/down the coller to get ride hight right staticly
change the rate of the spring to make it harder/softer

a damper only controls the rate at what your suspension can move in and out
bound is on closing, rebound is opening
we need to control this more than spring rates

if we dont have enough the body bounces up and down like its on a trampolene to much its like the suspension is locked up and also can have an effect on winding the ride hight down (too much rebound) or up to much bound as the car moves over the bumps and the damping slows movement too much.
small bumps in the road will show up to much damping and humpback bridges wil show up no enough when you get more tuned in.

[Wynand]

Originally Posted by robo

Because the spring/shock combo if correct in poundage would not be in the topped out position once the car was on the floor. Thats when the adjusters take over to trim ride height.

I hear what you say Bob as well as Baz-r. I still fail to see how the coil over adjusters will lower or raise the car, or maybe age is getting to me and stupidity moves in.

On my car - I made my own coilovers with Gabriel gas shocks and spent a lot of time working out the spring rates (courtesy of Google University )which seemed to worked because my car went down exactly to the designed height. No adjusting needed and springs nicely.
It is exactly as you said Bob.

BUT, and this pickles my mind, but hear me out - as my ride is now and I put another say for instance 1" tension/260lbs on the spring with the adjuster/perch nut, yes the spring will be shorter, but because spring loading is linear and when the car lowered back on the coilover, the spring will compress to exactly the same amount again iow, the car will get back to its original height as before the additional pre-load/tension added. The only problem I see is that the spring will now feel the cars weight and the 260lbs pre-load - sensing a higher load than actual carrying - and this extra weight has to be overcome before the spring function normally again
Does this makes sense or am I missing something.

Its not that Im nit picking, but its in my nature to be able to understand why things work the way it do, and if it works in this case, it just do not add up to my math and it drives me up a wall to now why not

[robo]

Think of it like this. Just to keep it simple lets say you have the right springs and the car is on the floor. The spring is now for arguments sake 6" long, so if you screw up the platforms an inch the spring will still be 6" long but the car will go up, same thing if you lower the car. The only time you would squash the spring more is if you put more weight on the car or they had weakened and you were over compensating with the adjusters to gain ride height, the spring would then be in bind. Hope this helps.

Bob

[Wynand]

Thanks Bob, I see now.
Shorter springs will indeed make the car sit lower and by adjusting the nut upwards, will lift the car on the spring and vice versa.
But this also means the shock will never be fully extended and when the wheel goes in full droop, (shock fully extended) the spring may come loose.

My theory was based om my units that were made from gas filled shocks and my here was how I went about it.;
I put the chassis on trestles and let the suspension dropped completely and then lifted (bumped)it completely and measured the travel and searched for a shock that have the said travel and will fit fully extended and compressed.
My shocks are gas filled and usually these extent itself fully unlike hydraulic (oil) units that does not extents itself fully.

After I made the adjustable coilovers I calculated the spring length that when fitted with a little pre-tension to tighten the spring in place, so its still 20mm longer than the max droop.
Then I made careful calculations, using correction factors for shock angles etc to have the spring rate that when the car is put on coilovers, it will be at the designed ride height - shock about 38% compressed, so when the spring goes into max bump, the shock still have a little movement left. When full drooped, the shock is about 95% extended.

As said before my car sits exactly where intended - 140mm (with driver) high and the springs sensitive for any input. I hope this will give a good quality ride because the suspension has a lot of travel and the spring rate perfect for car.
I need this because the roads in my area (rural) are very bumpy and in many places, potholes the order of the day - much so for whole of SA..
Here a pic on my self built adjustable coilovers, even done the ally anodising myself in the garage