Fishey

That with the idea of stock torsionbars being about 120# and stock fronts being around 160#

Skip so if its 56% effective, I get some 220# front springs and add rear coilovers( 100#) along with my stock Torsionbars. That my balance and handling should remain pretty neutral.

Oddjob

At low/stock spring rates, it seems that 944s are balanced with close to a 1:1 front to rear effective spring rate ratio. However, at higher spring rates, when getting into the full race suspension, you don’t want the rear effective rate to be equal with the front.

Ive found that somewhere around 1.3:1 to 1.6:1 front/rear eff. rate is where most 944s handle best for most drivers (using 90% eff front, 55% eff rear, 125 lb/in 23.5 mm T-bar). This is for full road course track use where you don’t want your rear end really stepping out on you (you may prefer to set up a car differently for autocrossing). Guys that like some oversteer, trail brake deep, and drive a late apex line, tend to go closer to the 1.3:1 ratio. If you drive a geometric apex (earlier turn-in) you will prefer around 1.5.

These numbers are for 944 Turbos and S2s, that do have a little tendency for throttle-on oversteer. A plain 944 or 944S without a lot of torque can probably run a bit higher rear spring because it doesnt have the torque to make the back end tail happy under power at track out.

Again there are a lot of additional variables that go into tuning the suspension. Wheel size and tire type (16x8s vs 18x9s on the rear make a big difference), alignment/ride height/corner balance specs, sway bars and settings, bushings, track surface condition, etc.

Im just recommending, before you go out and buy some trick suspension setup, do some research to find out what will work for you (so you don’t end up with several extra sets of rear springs in your garage). If you have the opportunity, drive some other cars that are setup for the track. See what fits your driving style and your comfort level. If you still street the car, I would stay under 400lb/in.

Skip

Fishey, the S2 had 24.5mm bars which equates to 149#. Most of the factory setups put the suspension bias as equal (relative to the weight balance) - a 160# front spring is ~144# effective.

As a reminder, the rear spring/torsion rate conversion is available here:

http://www.tech-session.com/kb/index...x_v2&id=22&c=4

Bryans951

So, tell me if I'm looking at all of this info correctly......

If I want to acheve a 1.3:1 ratio and I already have stock bars on the back and 250# springs on the front, then this should get me to spring rate for the coilovers for the rear.

x = desired overall wheel rate = 250/1.3= 192# right??
y = stock for 86 951 (for example 150#)
(x - y)/.56 = linear coil-over spring rate

so that would give me ...... (192-150)/.56= 75 This would mean that I would need 100# springs on the coilovers.

Am I doing this right???

Skip

Except that the 86 951 uses 23.5mm bars which are 129#. Looking for the rear spring to be (192-129)/.56 = 112.5. Either a 100 or 125 spring would do. I didn't follow the multiplier post too closely, but is the 1.3 charged against the actual front spring rate of the effective rate? The effective rate of a 250# front spring is ~225#... (173-129)/.56=78... so that's a 100 #spring. I prefer the easy method of balancing the car with regard to corner weights and deciding where to put more spring. In most cases, there should be a bias to the front. The above equation does the same as common math of matching the effective rates - if you have a 250# front spring that is 225# effective, and a 129# effective rear rate, you need to add x*56%=225-129... x=171 so, that's a 175 spring for the rear to make them equal... now use whatever bias you want... 1.3 would equate to 132 or a 125# spring for bias to the front.... potato/potahto

Fishey

Hey skip I think you could answer this question.
How was the Turbo RS supention done? give some specs
Like Torsion bar thinkness and front spring # also sways and shocks I am just intrested in what porsche thought was a good setup.

Bryans951

clear as mud! : )

Jason @ Paragon Products

Give me just a little bit guys and I'll get some specs together for you on the RS. Spring rates will vary depending on where the car was run. I have two setup sheets from when car #1 was originally tested and it had different springs on it between the two tests. I can tell you that my car currently has a dual Eibach spring setup on it and it's very stiff.

M758

Oddjob state exactly what I have learned and heared.

I run a set-up close to 1:1 on my ligthtned 944-spec car

350lbs coilovers front and 30 mm t-bars in back

With 90% effective front and the t-bar effective conversion rear I get

315 front and 335 rear. With my weltmeister bars and 225/50 tire on all corners I can dial in the set-up to my liking quite well. The car is stable enough in fast corners and still nible enough to rotate well in tigher corners. In this car this set-up is entierly effective and works with stock unmodified koni yellows.

Now go higher in spring rate and you may want more front stiffness bias to mantain the handling balance. I have also heard of this. However if anyone want to drive their car on the street any suspension more that 20-30% stiffer than mine is really overkill and will be unbearable even in full weight car.

Since very few of you guys are hardcore racers with dedicated race only 944's I'd forget about thse 1.3 and 1.5 ratios. Certainly for a 944 NA or S2 the 1:1 is about right. For a turbo may be 1.1 or 1.2 is better due to the power avalible and the tendance for these cars to have significantly more power than stock. For street car aps in high powered turbo 1.2 might be better not because it is faster, but possibly a bit safer on the road. Of course it may push too much at the track.


Now that all of that has been said there is one HUGE variable. The driver. Some guys like more oversteer. Some guys hate it. What is best for you is what makes you feel comfortable. If you are not comfortable in the car and how it handles you will not be able to get the max from it.

Oddjob

A little background:

The front to rear ratio I used is based on effective rates for both front and rear. Since it is a basic proportional ratio, it doesn’t really matter what exact constants you use for front effective rate (around 90%), rear coil effective rate (around 55%), and rear torsion bar rates (around 125 lb/in for a 23.5mm bar), as long as you continue to use the same constants for all comparisons.

For the Bryan’s sample question, my math is:

250(90%) = 225 front eff.
225/1.3 = 173
173 – 125 = 48 (rear eff minus t-bar)
48/55%) = 87 lb/in rear helper spring rate (100)

But like M758 said, my recommended ratios are for racing sprung cars, like where Matt H was talking about 600lb/in fronts. Below 300 or so, you do want to be much closer to a balanced front/rear eff. spring rate.

With higher spring rates (500 plus), I found that a 1.8 ratio (using my calcs) understeered badly, 1.3 oversteered. So I reduced the spring rate in the rear and have about a 1.5 ratio now, that can be controlled from slight oversteer to neutral with rear sway bar adjustments. For my sway bars, whl/tire size, and driving style that works the best. I know guys that like a much looser car and have theirs setup with close to a 1.3 ratio (ie 550 front springs, 450 rear helper springs with 23.5 mm T-bars). I know that Karl at Racer’s Edge was recommending around a 1.8 ratio (around 500 front, 450 rear coils w/o T-bars; or 200 rear helpers w/ 23.5mm T-bars).

The calculations are just a general rule of thumb to get you into the ball park of where you want to be for spring rates. You can use or calculate as a percentage, like the rear effective rate is 75% of the front effective rate, or the difference from a 1:1 balance. It doesn’t matter.

There will always be some trial and error involved with setting up a car. But I started my track testing without knowing what ballpark to be in, and I found out the hard way. I have 3 extra pair of rear springs on the shelf to show for it. Just wanted to give you guys some advice so you don’t end up with a similar spare spring inventory lying around.

M758

I also have some extra springs laying around.

250lbs stock diamter springs and 28 mm t-bars (yep I did the t-bars twice )

I really like my 350 / 30 set-up, but have considered a 300 / 30 set-up as well. In the end I think the 350/ 30 suits my car, the tracks I run and my driving style the best.

car_slave

Great info guys!!!!!!! Now lets talk sway bars. Personaly I'm driving an 1988 NA street car with 250lb front springs, with 23.5 t bars (I think. It's stock) and 200lb helper springs (KLA). Yes slightly more in the rear, but drives great. I get a little too much roll with the stock 27mm front and 18mm rear bars and 15" pd's. How do you come up with sway bar numbers for increased spring loads? I added a hefty 25mm rear bar to my 2003 Jetta GLI, and it made a big difference (it's also a front wheel drive). Is a larger rear sway the way to go in a 944?

Oddjob

If you have a 27mm front bar (actually 26.8) its not stock, thats a turbo S front bar. So someone thoughtfully added that for you already.

Next upgrade from your setup is going with the 968 M030 bars (30mm front, 19mm 3-way adjustable rear).

Thats about it for upgrading the front, but you can go stiffer yet in the rear with either a factory 21mm 3-way adjustable Cup Car bar (very hard to find now, probably over $500), or the 22mm adjustable Weltmeister bar.

There are of course some very expensive/trick bars available including **** pit adjustable setups. But those are out of the range of practicality and price reality for most of us.

M758

Personally I like the weltmeiseter 28mm Front and 22mm rear.

They are stiff, but what I like the most is the adjustability. Once I get the basic spring rates I can i use the sway bars to adjust the balance very qucikly and easily at the track. In fact I can adjust the rears in about 5 min. The prices are also reasonable.

car_slave

Thanks for the replies. The front bar actually has 27mm stamped on it, strange.