I am going to change out the sway bar(s) in the car and will probably go with the GT3 bar(s). I have dispensed opinions in the past and I want to see if you guys agree with it. Recall that I do have the PSS9's installed.

With the inherent understeer in the car, I was thinking of only replacing the rear bar while leaving the front stock. That way I can dial in neutral to slightly oversteering response characteristics. There is no question that a stiffer rear bar will do this. My reasoning for going with the rear bar only is that if both are replaced with the intent of reducing understeer, the addition of the front will actually counteract the effects of dialing out the understeer with a stiffer rear bar. In addition, since there is more mass in the rear of a 911 to keep flat through a turn, the rear only change makes additional sense. Lastly, the front bar is a PITA to change whereas the rear is a cake walk.

Opinions?

 

Stiffer rear bar will do the trick or just go with stiffer rear spings. The nice thing about the bar is you would have setting choice's. You might find that you'll like it a little softer with cold tires on slicker city streets than in track conditions.

 

Ken...you probably already know this, but Ruf just does the rear bar.

 

Cary,
Thanks. We should talk again sometime soon. I enjoyed our talk from a while ago.

John,
Yes, I did know that and this is actually another reason for my opinion.

 

Ken: That sounds like a good idea. I guess the only thing that could potentially be a problem would be that the back would be so stiff it could not be dialed into a neutral setting relative to the front stocker bar. But from what Johns is saying this doesn't seem to be a worry.

Mike

 

If you adjustable front and rears you can dial in the rear and/or dial out the front for oversteer....

 

Ken, You may recall that we discussed this at Lake Nockamixon. I have the FVD PSS9's and spoke with several sources about the sway bars. I ended up with the rear GT2/GT3 sway alone. There are four holes and mine is set 1 back from stiffest. At this point, the car is nearly neutral, with a tiny bit towards oversteer. The bar itself is thinner than the stock TT bar (!) but of course it allows for adjustability. The feedback that I received during my research on this topic was universal- rear bar alone.

BTW, the car looks awesome- I truly envy your ability to do this! Best Wishes in it. Also, I didn't originally think it could be improved upon in any way, but I believe Jeru might have proven me wrong!!

 

Very interesting and should work. I really like adjustablility so I will still do both but you can at least dial out the oversteer as everyone has said.

 

The rear bar diameter specs are as follows:

• Stock=21.7mm (non-adjustable)
• GT3=20.8mm (4 way adjustable)
• TechArt=23mm (3 way adjustable)
• H&R=24mm (3 way adjustable)

I originally wanted the H&R bar but I have heard they discontinued it temporarily due to fitup problems. It was nice since it incorporated the teflon sleeves in the frame mount bushings. That surely would have kept them quiet.
Is there any word on the re-introduction of these bars? Mike (AWE)?

 

I'll be the contrarian on this issue. I agree that adding just a rear adjustable bar will allow you to increase oversteer so as to counteract the inherent understeer of the Turbo. However, IMHO, if you want to deal with understeer, deal with it at its source -- the front of the car. Assuming cost is not an issue and you can get proper drop links, I'd go for the front and rear adjustable bar setup, just like the factory does and give yourself total flexibility in dealing with understeer/oversteer. BTW, you might be able to come close to dialing out the car's understeer by just playing around with the shock adjustments -- running the front shocks at a higher number (softer) than the rears.

 

Jack,
I appreciate your counterpoint. I have thought about this as well. I have tried to dial out the US with the shock adjustments and it doesn't seem to do it. I have had the backs at 2 and the fronts as high as 6 and stopped there. I want to do the f&r since I am a purist, but my fear is that the GT3 front bar on its most flexible setting will still be stiffer than the stock bar which reduces the ability of the rear bar to counteract it. The interesting thing is the GT3 rear bar is smaller than the stock TT bar whereas the GT3 front bar is larger than stock. Following are the specs:

Rear:

• Stock=21.7mm (non-adjustable)
• GT3=20.8mm (4 way adjustable)
• TechArt=23mm (3 way adjustable)
• H&R=24mm (3 way adjustable)

Front:

• Stock=24mm (non-adjustable)
• GT3=26.7mm (5 way adjustable)
• TechArt=23.8mm (3 way adjustable)
• H&R=25mm (3 way adjustable)

With the GT3 front bar starting out at 2.7mm larger than stock and the rear starting out at 0.9mm smaller than stock, I wonder if I would be fighting myself. I could easily calculate the torsional resistance if I knew precisely the perpendicular distances from the various drop link attachment points to the frame mounts.

 

" I could easily calculate the torsional resistance if I knew precisely the perpendicular distances from the various drop link attachment points to the frame mounts."

Ken can you say mad scientist ? I truley appreciate how far you will go to perfect you creation!

Keep up the great work!

 

Hey Darren,
When I was about 13 years old, I had a framed picture of a red Porsche Kremmer 930 Turbo over my bed. It has always been a dream of mine to own a 911 turbo. Having attained it, and being a tinkerer, and having my background in engineering, I am always looking to improve things a bit. It is funny since my previous 993 C2 remained bone stock in the time I owned it.
I guess 6speed can be blamed for some of this obsessive compulsive behaviour!!
Either that or I really am MAD!!!

 

Ken:

You're clearly a purist and a perfectionist, both of which are good things in my book.

I can't help you with the scientific calculations, but based upon my personal experience with the TechArt adjustable bars on my previous Turbo, I was able to dial out the understeer. One other point to make about the GT2/3 front bar, given the AWD/front suspension setup of the Turbo, I believe you will only be able to access 3 of the 5 adjustment (holes) on the front bar. Since it's the two inner most holes (stiffest settings), their inaccessibility should not cause you a problem.

 

KPV,

The problem with being too much of a perfectionist in this area is there are so many real variables at hand.

When talking about the Anti Roll Bars size, keep in mind a couple important points. Not only are the front and rear bars a different diameter and wall thickness (which nobody has pointed out yet) but the torsional length and the lever arm lengths on both bars are completely different which has as much effect as the diameter. It’s a simple equation to calculate the bars stiffness in LB/INS but, just as important is to calculate the moment at the ARB pickup and divide that by the moment at the wheel (wheel rate) and this tells you the effect the ARB is having on the roll. If you do this it will be clear that talking about 23mm rear bars and 27 mm becomes pointless as far as using these numbers to “logically” figure all this stuff out because the geometry changes the end number. Now, to “scientifically” figure the handling on a car you have to figure in all the rest of the cars variables as well …. Welcome to the world of mental masturbation!!

You can make some changes with shocks but they should be used for the “fine” tuning rather than the major set up. The primary reason for the shocks (Dampers) is to control the spring action, NOT to change it. To respond to the earlier statement about shocks, rebound will effect a car like an ARB at the EXIT of a turn but not in the initial turn in. This is where too many adjustments can be more of a problem for consumers than help. I can’t tell you how many times I’ve gone to the track and brought parts to set up a car only to find they already had everything, it just wasn’t dialed in correctly.

If and I’m saying “IF” you feel the front bar is the correct size for you, keep it. Almost all the time tuning is made at the rear of a Porsche. This is because the greater amount of weight is at the rear and you will get largest results by adjusting that end first. Not to slam the earlier comment about changing the front because “that’s where the problem is,” again, it may seem the logical answer but, it turns out that it isn’t necessarily true. The cars were build new to push and you’ll find the fastest results from the rear.

One last think to remember is how low your car is. The lower your Roll Center is the less effective an ARB becomes…. Just one more variable to consider