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914World.com _ 914World Garage _ Suspension mods

Posted by: TonyAKAVW Feb 4 2005, 05:39 PM

I just installed a few things on my 914 that I stripped off of my old car that met its fate with rust.

My car now has: stock 15mm front sway bar, KYBs in front and back, stock torsion bars, and 140 lb springs in the back. I'm not certain of the springs being 140 lbs, but they are definitely stiffer than stock, and waaay stiffer than the old saggy ones I pulled off the car.

I don't know much about suspension and I haven't driven on a track, but I think that the car is oversteering now and it makes sense based on the fact that the back is now stiffer than the front.

So the question is, what do I do now? Stiffer torsion bars? Stiffer sway bar?

-Tony

Posted by: bondo Feb 4 2005, 05:41 PM

Topic says understeer, post text says oversteer. I don't know about your car, but this thread seems perfectly balanced

Posted by: ChrisReale Feb 4 2005, 05:42 PM

Get a stiffer sway bar up front. That way you can adjust it to act like you are using stiffer torsion bars, but without the jaw rattling ride. I had 22mm bars up front and a Tarett bar. Now I use stock torsions, 200# rear springs and use the front bar to adjust the under/oversteer

Posted by: TonyAKAVW Feb 4 2005, 05:48 PM

QUOTE
Topic says understeer, post text says oversteer. I don't know about your car, but this thread seems perfectly balanced

yeah I just noticed that. OOPS!!

QUOTE
Get a stiffer sway bar up front. That way you can adjust it to act like you are using stiffer torsion bars, but without the jaw rattling ride. I had 22mm bars up front and a Tarett bar. Now I use stock torsions, 200# rear springs and use the front bar to adjust the under/oversteer

That makes a lot of sense. I have never really understood how you adjust a sway bar though. The only thing I can think of is that you are putting pre-load onto the sway bar one way or the other. Is this true?

Posted by: SLITS Feb 4 2005, 05:50 PM

You adjust a sway bar by lengthing or shortening the arm....translates to increased or decreased torsional twist of the bar for a given wheel movement.

Posted by: redshift Feb 4 2005, 05:52 PM

Dropping the nose makes her dig in more too.. but what Chris said.

M

Posted by: TonyAKAVW Feb 4 2005, 06:01 PM

QUOTE
You adjust a sway bar by lengthing or shortening the arm....translates to increased or decreased torsional twist of the bar for a given wheel movement.

That makes perfect sense! Now the followup question to that is... What range of adjustability do I have? With the stock setup everything is fixed, but I could easily fabricate new arms that have a line of holes. But at some point, as I get closer to the bar, the geometry of the linkage to the A-arm will get wierd, and the bar itself might suffer from all the torque????

Are there any rules of thumb as to how much stiffer I want to make things? i.e. if I made the back twice as stiff as it was, do I want the front to be twice as stiff too? And how does the increase in stiffness of a sway bar affect the overall stiffness of the front? I realize that this is only stifness with respect to turning, but does a sway bar thats twice as stiff result in a front suspension that is twice as stiff?

-Tony

Posted by: Dave_Darling Feb 4 2005, 06:16 PM

I don't think you'll have enough adjustment simply by making adjustable arms for the stock setup. I would recommend a 19mm bar at the minimum, and a 21mm would likely be a better idea.

I'm guessing that, since you went from "about" 65#/in rear spring rate to 140#/in, that you would want to roughly double the stiffness of the front suspension.

--DD

Posted by: jkeyzer Feb 4 2005, 06:33 PM

Tony, I think to adjust a bar you change the length of the "arms" on the bar, not the drop links.

You need an adjustable sway bar, although I have seen people flatten more of the bar and drill more holes (not on a 914 though). I don't think there is much room to do that on a stock bar.