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914World.com _ 914World Garage _ Question for sway bar/suspension Guru's

Posted by: rick 918-S Mar 12 2005, 07:33 AM

My car has a push at high speed in tight corners. It wants to slide the front to the outside of the circle. I need to increase front grip. I was talking to a local car guy here and he told me I should has a big rear sway bar. I tend to believe him. He used to work for the Archer Brothers in their race shop. But maybe his theory doesn't apply to middle motor cars.

Who has experience with this? Show me your sway bars. Specially rear ones.

Oh ya, what about tire pressure.

I encourage long explainations. But talk to me like I'm a 4th grader.

Posted by: Cloudbuster Mar 12 2005, 10:03 AM

The way this swaybar thing was explained to me was:

The more compliant (softer) end of the car has load distributed more evenly between the inside and outside 'tiars' -- more grip. The harder end puts more load on a single 'tiar', causing it to come unstuck sooner.

Since the front is pushing (sliding first), it has a higher spring rate. The options are

1) Decrease the spring rate in the front either by changing out torsion bars, or softening up the swaybar by moving the droplinks farther out on the adjuster arm.

or

2) Increase spring rate in the rear by adding heavier springs, or adding a swaybar.

Heavier springs is probably easier.

You don't necessarily need a rear swaybar. I took my 914 from stable, to extremely tail-slide happy by using 200lb springs in the rear. This has since been fixed by adding a Tarett bar in the front.

Posted by: rick 918-S Mar 12 2005, 10:15 AM

Ok that makes sense. As a note to the first post. I have no sway bars front or rear, stock torsion bars and springs, stock tie rod ends.

I think the 928 motor is causing a higher center of gravity change the polar moment.

I have a set of 180 lb rear springs. I think I'll try them first.

I may like to install a rear bar as well.

What about tire pressure?

Posted by: SirAndy Mar 12 2005, 01:12 PM

easy to remember:

- if the front is lose, tighten the rear

- if the rear is lose, tighten the front

you can tighten by adding more sway bar (dial in more or go bigger on the bar) or increase spring rates.

Springs:
for the front, that would be bigger torsion bars, for the rear, that would be heavier springs.

Sway Bars:
to tighten the front, move the droplinks towards the rear of the car.
to loosen the front, move the droplinks towards the front of the car.

if you don't already have a rear sway bar, adding one will tighten the rear.
it's the equivalent of adding more spring rate to the rear.

also, if the front is pushing (understeer) and you don't have the option of going stiffer in the rear, you can loosen the front bar (make it softer) which is the equivalent of tightening the rear ...

easy, eh?
Andy

Posted by: trekkor Mar 12 2005, 02:40 PM

QUOTE
Show me your sway bars. Specially rear ones.

OK

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Posted by: trekkor Mar 12 2005, 02:41 PM

rear is stock bar, 150# springs on Koni's

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Posted by: Aaron Cox Mar 12 2005, 02:42 PM

yup. im running a stock rear bar with 140's..... a tad too much oversteer at speed ....so i need to dial in more sway bar in the front

im throwing on 180 lb springs and 21mm torsionbars.... because i dont lik emy brake dive and throttle squat....

Posted by: Andyrew Mar 12 2005, 02:45 PM

Isnt a stock sway bar about 40 lbs of suspension force about? In relation to spring rates??

I was thinking of going with 225lb springs, or 180lb with a stock or adjustable sway bar on the rear.. My front is way to tight for the rest of my suspension... lol

Andrew

Posted by: trekkor Mar 12 2005, 02:46 PM

front

31mm Schmart

KT

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Posted by: Aaron Cox Mar 12 2005, 02:50 PM

T dog,

what t bars you running?

i got me some 180 springs....need to find some beefier t bars......

Posted by: ArtechnikA Mar 12 2005, 02:53 PM

tire pressures:

a fine-tuning device to be tinkered with after the suspension is fundamentally balanced.

Posted by: trekkor Mar 12 2005, 02:57 PM

QUOTE
what t bars you running?

Stock...

KT

Posted by: Aaron Cox Mar 12 2005, 02:58 PM

QUOTE (trekkor @ Mar 12 2005, 01:57 PM)

QUOTE
what t bars you running?

Stock...

KT

brake dive central? or you firm up them konis real gud

Posted by: trekkor Mar 12 2005, 03:02 PM

QUOTE
tire pressures:

Some of my findings:

Falkens- 41psi rear/39psi front
Yokohama A032R- 35psi rear/33psi front
Hoosier R3S03- 26psi rear/24psi front ( may go lower )

KT

Posted by: trekkor Mar 12 2005, 03:05 PM

QUOTE
brake dive central? or you firm up them konis real gud

Koni's full firm.

Here's full brakes at 70mph.

KT

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Posted by: gaz914 Mar 12 2005, 04:33 PM

To complicate the matter a little more for you Rick, understeer can often be cured by adding a front sway bar - contrary to the advice above.

The reason is to do with the camber change that happens due to the body roll when cornering. Particularly with wider tyres, the tyre no longer sits "flat" on the road when the body rolls excessively and of course the grip generated is less.

By adding a sway bar to the front, the camber change may be limited to such an extent that the actual grip generated is better than before, despite the added weight transfer that should make less grip.

That is: PLUS grip via less camber change > MINUS grip via weight transfer.

If the front bar is too large (in combination with the spring rate) then more understeer may be the result.

In your situation, I would consider trying a small-ish (standard?) sway bar for the front first to control the body roll/camber change. If the understeer is not reduced sufficiently or is worse, then a rear bar would be needed, experimenting with and without the front bar connected.

GAZ

Posted by: jim912928 Mar 12 2005, 04:43 PM

Rick,

I put factory sway bars on my front and rear....made a huge difference in driving it on the street. Haven't AX it yet...but it sure made a huge difference on normal twisty roads! I've been told you can run with a front sway bar and no rear...but I've always been told not to run with a rear sway bar unless you have a front one installed.

Posted by: rick 918-S Mar 12 2005, 06:51 PM

Thanks for all your suggestions. I'm taking it all in.

Posted by: Travis Neff Mar 12 2005, 08:31 PM

Here we go, 22mm Welt sway bar. Watch out for the duct tape, someone drilled a hole too low.

22mm Sway Bar
22mm Torsion Bars
Welt street bushings
New ball joints
Turbo tie rods (cheapie, non castellated nut ones)
Cleaned and regreased rack
New Rotors, bearings & rebuilt calipers
Koni Sport Shocks

Rear,

Koni Sport Shocks
150lb springs on threaded perches
New Rotors, pads

I am sure with this setup I will need 180-200lb springs. Old car if pushed would oversteer without the front sway bar and 150 lb springs.

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Posted by: Travis Neff Mar 12 2005, 08:31 PM

uno mas

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Posted by: Jeroen Mar 13 2005, 07:42 AM

Rick, if you have no swaybars and stock springs right now, going up to 180# rear springs (and no other mods) will cause a lot of oversteer (tail stepping out)
In your case, I'd try a stock front bar and some 140# rear springs first (no rear bar)
A rear bar may cause wheelspin in corners if you don't have a LSD

Just my €0.02