Front springs lower than SSL?

[Not_An_Abba_Fan]

Unless you have staged damping rates in a shock (Monroe Sensa-Trac for example) the valving and damping rate is the same through the length of travel. Changing to a heavier duty damping rate is benificial with lowered springs so they don't bottom out as easy, but the only thing that shortened shocks/struts do is to not extend more than the free length of the spring so they don't unseat. The damping rate is the same throughout the full travel of the piston.

 

[ephect]

Thanks NAAF, I've always been told there's an optimal range that's affected when lowering or raising. Now I know.

 

[Not_An_Abba_Fan]

Believe it or not, the damping effect actually gets better on a stock shock when lowered. The part of the piston that is in constant use at stock height will wear slightly allowing a minute amount of oil to bypass the valving. Lowering the car moves the valving to a "fresh" part of the piston so it actually gives the impression of improved damping.

Replacing shocks and struts with a heavier damp rate is recommended though.

 

[yxyx64]

to clarify - the damping rates in a short strut are not the same as the rates in a standard strut. Compression is hard to tell, but mainly rebound damping rate is greater for the reasons said above.

Coil bind and bump stops are to stop struts bottoming. Compression damping is about oscillations.

For a lowered spring the rebound is harder so that the spring energy is released over a shorter distance (normal working travel distance not the full bloody free length of the spring saga discussion thing previous) - this changes the work and power associated with the extending spring. Work here is a technical term. Power is also a technical term.

In simple terms (stop reading here immortality as this is simplified for the masses, and yet still very true) to do the same work over a shorter distance requires a more powerful damper.

Get short struts with lowered springs is the message, or have oscillations.

 

[Immortality]

LOL, no problems here from me. Shorter struts/shocks with shorter/lowered springs :thumbsup:

Simply physics really, the shorter strut has to control more energy being exerted in a shorter distance than a standard spring/strut combination.

 

[Not_An_Abba_Fan]

Ummm...the opposite actually. Lowered springs have a higher rate than standard height springs. They will compress less with the same load applied as a stock height spring, so in actual fact, the energy given off from a lowered height spring is less than a stock height spring. The reason for a heavier damping rate is that the lowered spring will not compress and rebound as fast as a stock height spring, therefore the valving in the shock won't slow the oil down to provide adequate damping. A higher damping rate will.

While I said a standard shock or strut will still work with lowered springs, I also said that heavier shocks are recommended. The "harsh" ride experienced with standard shocks is due to oscillation. The car will "feel" like it is harder, but because the springs have a higher rate, the "bounce" is quite hard. Heavier shocks eliminate oscillation so you won't get the "harsh" ride.

 

[Immortality]

Ummm...the opposite actually. Lowered springs have a higher rate than standard height springs. They will compress less with the same load applied as a stock height spring,

Right, a lowered spring will compress less than a standard spring when hitting the same bump, however the stored energy would be the same due to the higher spring rate.... the strut would have to control that same energy on the rebound but have less travel to do so, hence the need for a firmer shock absorber

 

[yxyx64]

opposite of what? maybe my english as second language is the problem here - but I read mine again and thought it ok.

Dampers are all about controlling the spring - very little about absorbing the impact from pothole or whatever. With higher spring rate you must have higher rebound damping or oscillations increase to bad levels and car will crash or people get sick. You must do most of the control on the rebound, as whilst possible to control spring on compression it would mean an unacceptable harshness on compression (way too hard when you hit a pothole) so it is not done for cars.

If you compress any coil compression spring and then let it go it will return to original length BUT before doing so it will overextend, then underextend, then overextend.....etc boing, boing, boing, boing..........this is spring oscillation. The dampers are used to control this oscillation, NOT absorb the initial impact that compresses the spring.

 

[Not_An_Abba_Fan]

I understand that, but a lowered spring having a higher spring rate will not compress and rebound as much as a stock height spring, so the energy released is slightly less as it doesn't rebound as much.

 

[yxyx64]

I understand that, but a lowered spring having a higher spring rate will not compress and rebound as much as a stock height spring, so the energy released is slightly less as it doesn't rebound as much.

For this you should consider the energy is the same (unless you change weight or velocity or whatever). It is the distance over which the energy must be dissipated by the spring that varies. For the same work over a smaller distance you must have greater forces. Its a physics thing. It is the greater forces you are now having to control.

how to explain - (this will be simplified so not exactly true immortality) 2 same cars hit the same pothole at the same speed so both front ends have to absorb the same energy. One car dips 6 inches because standard springs. Other car dips 2 inches because on superlows. Same energy though to be absorbed by each car (same weight, same speed etc). After pothole springs uncompress back to normal height. Standard car has 6 inches to get rid of energy - superlow car has 2 inches to get rid of same energy. The superlow spring requires a much more stronger controlling damper while it extends than the standard car does because the superlow is much more explosive when it returns to normal height ( a function of higher spring rate at its useable travel range)