Springs for track car...

[4est]

For a full-on track 993, how much usable stroke do I need for the front and rear. The springs I'm looking at have right at 4.0" full stroke and right at 3.0" of usable stroke. These are Swift springs in 728 for the front and 840 for the rear. I will use 45 lbs. helpers to keep the springs seated at full droop (mostly needed for the front). 993 C4S converted to rear wheel drive only, full monoballs all around, around 2600 lbs, Factory Bilstein 993 RSR shocks...

[kurquhart]

728 lbs front, or is that a model number?

[4est]

Lbs.

[kurquhart]

46/54 split seems like a recipe for push to me, but I am no expert on 993. FWIW, I have a 40/60 split on my 964.

[4est]

I'm not set on the spring rate. I will decide that at a later date, with input from those more knowledgeable (pretty much everybody). What I am looking for is input on stroke length, so I can get the right length spring.

The springs that just came off it are H&R 6" springs (400 and 571) with a 280'ish tender. The full length of both springs was 9.25", including the collar. The front, at full droop would dislocate by about .25" (not enough to cause problems), and the rear was pre-compressed down to about 8". The front, when weighted, compressed to right around 8" also. So, when it took the shocks off, the rears show an overall, unloaded length of about 8" (a little over an inch of precompression) and the front springs were loose by .25 or .125" (out of a 9.25" stack heighth). Again, when the car was sitting, the springs measured about 8" front and rear.

I have been told by someone I trust to get the shortest spring I can. I like the ride height it's at (+/-), so I think the spring height setting on the shock is in the ballpark (+/-). So I am thinking a 7" spring for the front, with a 2.75", 85 lbs helper will keep the spring from dislocating at full droop, and be right at 8" when loaded. For the rear, I was thinking a 6" spring with the same helper giving me a.75" preconmpression and then a 7" loaded spring (+/-).

The problem started when I had the now defunct CENSORED put the shocks off their shopcar on my car. They talked about the progressive rate of the combined spring (blah, blah, blah..) What really happened (I'm no mathmetician, so don't take me to the formula) is that I got some kind of funky, progressive spring rate that never approached the 400/571 range and gave my car a ton of travel, especially noticed in the front. At the last TT, my car dived under braking and bobbed from side to side under lateral g so bad that a novice like me noticed. It performed better with the PSS9s. It also rubbed holes in the fender liner of both front wheelwells (pretty badly).

So: I need to know what springs to get, and will take all input under advisement. Spring rate, stroke, et al. For the pros, (Jae, Steve, Phil) what length spring would you spec for a HD Bilstein with a threaded ride-height adjustment for a 993?

My head hurts now, so I'm gonna go lay down.....

[davidsq]

whoz phil

[LUCKY DAVE]

Phil is "Hot shoe" Jackie Corwin's tuner.


and husband......

[4est]

Thanks for all the input/help everybody.

[4est]

I find it a little disconcerting that well over 600 people have viewed this topic, and only one had anything to say. Are the specifications on spring rate and stroke length rocket science that no one will delve into or are these values 'close-hold' information that no one will share. We get 12 pages of DOT vs True Slick and nothing on this. Maybe we should have a tech session that will answer the multitude of questions that we have and the complete lack of answers. Over 600 showed interest, only 1 answered anything at all...

[Steve Grosekemper]

4est,

It is my opinion you haven't gotten and answer because there isn't just one answer.

Suspension is like shoes. What fits one does not always fit all. It doesn't make that set-up wrong... just wrong for the driver.

You must start with a mathematical baseline set-up and make adjustments from there.
First you must know your exact wheel weigh to choose spring weight.
Then adjust those numbers to your driving style. (I like more over steer than others might be comfortable with) A Big Willow car is going to need to be stiffer in the front for under steer than a car set up for SM/BW/SoW. Once you have the spring rates set, you can select the shock valving. Most people don't increase the rebound enough on really stiff cars and end up with scary handling under braking and through undulating sweepers.

Short springs are a good guideline for unsprung weight but this is not a rule. Spring length depends on shock droop length, threaded body length and ride vehicle height. Helpers should collapse completely, and progressive springs are for street/tack cars. Full track cars should have single rate springs.

All of this is purely my opinion, and others may completely disagree.
But, I find it much easier to set up a car for someone I have driven with and know their driving style before suggesting a set up.

Setting up a car is like being a fine tailor; it is more about the guy wearing the suit than the suit itself.

[Jad]

Plus, once the car is basically set up, you still change tires every couple of months and get lots of input on what different tires do. Few, if any of us really change springs very often to get much valuable input on what a 50lbs difference in front spring really does. I can tell you 1600lbs is too stiff for a 996 racecar at AX, and the factory springs are too soft for a 996 Targa. The 800 and 1000lbs springs on the racecar now are somewhere close, but I can not tell you they are right. And as Steve said, that is probably because they are too stiff for AX, but OK for big tracks. With the old tires, they are too stiff everywhere. I guess without a full racing budget to do several test sessions and change springs and shocks for every event, you are just going to have to get a reasonable setup (500lbs to 1000lbs for a rough range) and make the best of it in my opinion.

Good luck! and don't forget you have the excuse the springs and shocks were all wrong for the track, otherwise you would have had TTOD!!!!

[va122]

I just went through this and went with the wrong spring length in the rear, I had 4" springs all around with different rates F/R obviously with 2" helpers. I was running out of droop in the rear and had a hell of a time keeping it on track. And this was done by a pro-race shop. Fortunately a saint at Moton set me straight with a 6" and the car is perfect.

My advice is to call one of the pro shops that raced 993s TRG, Farnbacher etc and ask. They are usually very nice.

Or actually, call Jae Lee at Mirage.

Good luck and be patient.

[Mike]

Your set up seems common, Jae could tell you your options.
Call him 1 858 581 1101
Here's my 911 getting the best springs...
Jae w/sway bars disconnected completed a spring and shock scan.

[4est]

Why do you need to know the wheel weight for determining spring rate? The wheels and tires are 'unsprung weight', so how do they determine proper spring rate? I have several sets of wheel/tire combinations; Carrera Lightweights w/Hoosier slicks, Twists w/ RA-1s, etc. should I lean more towards the heaviest or lightest in factoring for spring weight?

[Steve Grosekemper]

Why do you need to know the wheel weight for determining spring rate? The wheels and tires are 'unsprung weight', so how do they determine proper spring rate? I have several sets of wheel/tire combinations; Carrera Lightweights w/Hoosier slicks, Twists w/ RA-1s, etc. should I lean more towards the heaviest or lightest in factoring for spring weight?

Sorry I mis-spoke,
By wheel weight I mean how much weight is at each tire or corner.
A 993 with 900 pounds at each rear corner and 600 pounds at each front corner is going to have different spring and shock settings than a similar weight 944 turbo with 750 pounds at each corner, just as a 2000 pound 911 will be different from each of those.

Then factor in driving style, track layout, wheel and tire size and stick, aerodynamic package, drivability, cost and about a dozen other factors.

That's why most people thow in a fairly close package and make adjustments as they go.
Thowing a package together that is going to be perfect is very difficult, if not impossible.
Doing it for multiple tracks only complicates the equasion.
That's why the big dogs in POC are so fast. They only run one track with one setup...
Much easier.