I was curious about how coilover height effects spring rate. I have heard that raising up a coilover creates a higher effective spring rate than lowering, because you are actually using the full compression of the springs (and shocks/struts for that matter). That by raising up your coilovers in back, lets say, the extra travel gained will act to stiffen the rear, not loosen as it might seem. Can anyone confirm this? Had some issues last year with controlling understeer/oversteer while autocrossing when playing with ride height and would like to get a better understanding of the way perch height effects the handling. TIA.

 

Changing ride height doesn't change the spring rate.. usually coilover are fixed rate springs... (ie: it takes 400 lbs to compress the spring 1" or 800 lb to compress 2"... etc)
the ride height changes the amount of weight distributed to that wheel.
This is how you adjust cross weight to change handling characteristics of your car

Check out the ground control's website on corner balancing:

http://www.ground-control.com/gctalk4.htm

 

All it does is chance the height. (for all I know)

 

Sorry, I wasn't more clear. I guess what I meant was would raising or lower have similiar effects to changing spring rates, as I have heard?

 

Not as long as you aren't pre-loading the spring. Which gets back to the whole corner-balancing thing...

 

There has been some discussion about changing roll-centers when changing ride height and how that requires the use of higher spring rates when lowering a car.

Shine racing claims this on their website http://www.srsvw.com/page5.htm and it often incited heated debates on the VW mailing lists I used to be a member of.

In an event, here's an excerpt of what they say. Note: this applies to macpherson strut type front suspensions and may not be applicable to a double wishbone or other suspension type.

From Shine website: "Lowering a VW too much has several bad effects. The Macpherson Strut front suspension has some design limitations, one of which is limited suspension travel. A1 cars have the least, A2 more and A3 even more, but there really isn't very much to work with. Every inch you lower the car is one inch less suspension travel than before the car bottoms (unless you use shorter struts). To counteract this tendency to bottom the springs must be made proportionally stiffer, the lower the stiffer. Most people assume that radically lowering the car will improve the handling because it lowers the center of gravity-This would only be true if you could alter the suspension geometry to match the new ride height. As the front of a VW is lowered, the center of gravity is lowered, BUT, THE ROLL CENTER IS LOWERED AT A MUCH FASTER RATE. What this means is, the lower you go the MORE the car wants to roll. To compensate, the springs have to be stiffened to the point of rediculous. "

 

Bottoming out the suspension applies to Honda A-Arm designs as well. Want an example, find some kids in Civics at your local mall.

I can think of 2 ways changing the ride height can affect the handling of the car.

1) Center of gravity
2) If the car is too low, and bottoms out.

Now .. this thread is actually kinda close to home for me. I just switched to GCs from Pro-Kits. I have 8 inch 400# ERS in the front. The car now sits about where it was with the pro-kits, maybe 1.3-1.5 inches lower then stock. Looking at the strut, there is about 1.5-2 inches of travel up front. I have the bump stop cut half way. Do you guys think this is enough with a 400# spring? GC web site sais 4.76 inches total travel for the 400#. Not sure how much it has compressed with just the car sitting on it

I am taking the car to a local shop for alignment and input on the ride height tomorrow. Any thoughs from you guys?

 

The effective spring rate can change for different ride heights dependent upon the suspension geometry. Motion ratio isn't necessarily (and isn't usually) a constant value. I have no idea about our cars in particular, but typically there is rising leverage as the chassis is lowered with respect to the suspension.

The actual change in rate over the limited range of travel we are discussing may be minimal, you'd have to figure out the motion ratio and transmission angle as a function of ride height to see either way.