Performance springs

[boogiedude]

So in my search for performance/lowering springs I've been forwarded to a site called pitstopusa.com by several of my friends who autocross/build performance street cars. This site basically stocks large amounts of performance parts ranging from drive train components to bushings and springs. The only problem is anything I order from them wouldn't necessarily be designed for our cars.

Here comes the part where I need help: I'm not the most educated person when it comes to how spring rates/heights and such work.

On IAP, their performance springs set consists of fronts that are 12 1/4" tall with a rate of 214lbs/in; and rears that are 16 1/2" tall with a rate of 116lbs/in. And 9 & 10 coils, respectively.

On pitstopusa.com, they have their springs organized by front and rear sets and you can mix and match to get your desired ratios. Depending on brands, the front springs range from 8-12" in height and rates of 500-1500lb/in. Rears range from 8-16" in height and rates of 100-500lb/in.

The IAP spring rates seem kind of low to me(keep in mind that I'm not afraid of a stiff ride, and would gladly sacrifice some comfort for greater handling/maneuverability. Fast corners make me happy.) in comparison to what I have found on this site, and from what friends of mine run in their cars.


Questions start.... now.

1)What exactly defines the spring rate?
2)If I increased the spring rate, could I use a slightly shorter spring and maintain the same height as a softer, but taller spring?
3)Is there any physical difference between front and rear springs? Or is it most likely just organized as such on the site to group springs of similar size/rates?
4)The rear springs on both pitstopusa, and IAP seem dramatically softer. Why?
5)What is the ideal ratio of front:back rates?
6)What is the max spring rate I should use?(I'm assuming if it gets too high, I run the risk of damaging the shock towers)
7)Anyone know the stock rate?
8)Any other information you feel I should know, or would like to share?

Keep in mind that I'm looking to be educated, and I'm not going to pretend that I know what the best solution is so feel free to give me any feedback you like(as long as it's flame free )

I'm also hoping this thread could serve as a collaboration of questions/answers about upgrading suspension for those of us who don't come from racing pedigrees (similar to the seat FAQ)

[MNspiderman]

I had a 99 Dodge neon R/T for a while. It was running 700lb springs in the front corners. At the moment i can't remember what it had in the rear. They are similar in size and weight. It held the corners very well.

[maytag]

well, I am not the most educated here either, but I'll see if I can't confuse the issue with some general ideas:

Typically, if you intend to use spring rates rather than spring length to set ride-height, then you will need stiffer springs, which you already know. Something you'll want to know (and I don't) is how much static preload the original spring has? In other words, with the car at rest, how far is the spring compressed as compared to the spring at rest (not installed)? This shouldn't be hard to measure, as somebody here undoubtedly knows the uninstalled height.
As I understand it, spring rate refers to the force exerted during the first inch of compression. now, theorhetically, a linear spring rate will create a consistent measurement for every inch thereafter, where a progressive spring rate will increase the force as the compression increases. (my guess is that you will find mainly linear springs on the site you are talking about, and that is most common anyway, unless you're into motorcycles).
SO: again, just theory here; if the weight on the front right corner is 500lb (as measured at the spring perch) then a 500lb spring will compress 1" when the vehicle is at rest.

this should help you answer half of the reason why the rear springs are significantly softer than the fronts: where is the car heaviest? the other part of the "why" is all about weight transfer. when you are braking and / or turtning, your weight will invariably transfer to the front of the car, loading that end and unloading the rear. you will almost NEVER see the rear springs loaded heavily. there may be 'some' corners on some racetracks where the design of the corner will result in the loading of the rear, but clearly the front is the most important. rememebr too that sometimes a component of good handling is using that weight transfer to help rotate the car (particularly in an underpowered car where you can't use the throttle to do it for you). I'm not talking about sliding, I'm only talking about geometry here. Sometimes you NEED to get that rear end to do more than just follow the front. This is why some people do NOT add a rear sway bar. (even though for most of us humans, adding one makes the car easier to manage in high speed corners.)
But don;t forget that a stiffer spring will require significantly more damping as well. You'll want to match your damping rates to your spring rates in your search for great handling.

Now this is where I'm done. I do NOT know any specifics about spring weights on this car. I don;t know measured weights. I don't know what the "ideal" ratio is. I'll be watching this thread closely to see what the pros tell ya., and opefully I'll learn some stuff too.

I'll even add a couple more questions into the mix:
What is the optimal 'height' for the vehicle? Looking at the A-Arms, it's clear that lowering too far will creat a real issue with the A-Arms being well past their 'fulcrum' (is that the correct term?) I like the lowered car, but I prefer a handling car. So I've considered building a drop-spindle of sorts, that would maintain the stock geometry, but lower the car at the unsprung area. What kind of problems (beyond fabrication) will I encounter this way? And am I making to big an issue out of that?
I've driven many purpose-built race-cars. The ride was clearly impractical for the street. But I don;t need a race-car. there's got to be a good combination. something that'll be just barely comfortable enough on the street, but perform well when I hit the racetrack for a track day a couple times a year.

So I'll go into 'watch' mode, and hope I didn;t confuse the issue too much?

[engineerted]

Lets start here with some education. How is the spring rate calculated.
http://www.therangerstation.com/tech_li ... ngrate.htm

Now, how do I select the proper rate for my car? You need to know the weight of the car and how much of the weight is carried at each wheel. Thus to get these numbers you need to have the car corner weighed, not a big deal for us racer, they have scales at the track we can use, but I have never weight my street car. Now if some one chimes in and provides the stock spring rates for the spider then you could calculate the weight at each wheel by measuring the compressed spring length and the free length. Does this make any since now? Sorry I do not have any numbers for you but other has done this and someone will chime in here. I hope this gives you a start.

Ted