RSAErick

While in the process of replacing the rear sway bar on my RSA with a 19 mm 3-way adjustable sway bar, I found a surprise...

I thought that the RSA was fitted with a 20 mm non-adjustable rear sway bar. However, there was a 21 mm non-adjustable sway bar installed, with the part number 964 701 07 stamped on it (probably implying 964.333.701.07).

I searched the archives, and found the following list of available 964 rear sway bars (provided by Cuppie):

18mm: 964.333.701.70 Carrera 2 RS only
19mm: 964.333.701.12 Carrera 2 M249 (tiptronic)
20mm: 964.333.701.06 Carrera 2/4 91- M481 (manual)
21mm: 964.333.701.07 Carrera 2 -90 M481

My questions are:

1. What were the RSA's originally fitted with? It's amazing to think that after 2 years of ownership, regular Rennlist reading, and ownership of Adrian's book, that I STILL don't know the size of the rear stabiliser bar that was mounted on my car!

2. Should I replace the rear sway bar with the 19 mm 3-way adjustable bar? I have the standard H&R coilovers installed; the car is lowered, with about -2.1 degrees of camber. I would like to minimize the annoying understeer experience during track driving. But considering that the rear sway bar is 21 mm, compared to the 19 mm bar that I am considering replacing it with, would I be better off staying with the thicker bar to minimize understeer? Or will adjusting the 19 mm bar to full "firm" provide a "stiffer" rear?

Thanks for your advice.

Erick

Adrian

Dear Erick,
The RSA came standard with 20 mm. Obviously somebody has replaced it since new.
Replacing with adjustables is a completely different kettle of fish so my advice is to fit it and see. Remember the RS had a 3-way adjustable 18 mm rear sway bar.
Ciao,
Adrian
964C4

BGLeduc

The tough part is knowing how a 19mm adjustable will compare to a 21mm non adjustable. As you probably know, its not just the size, but the length of the arms that contribute to overall stiffness.

Its not impossible that a 19mm using the holes that result in the shortest arm may be stiffer than a 21mm if the holes are at the end of the arm, as they likely are.

Fred Puhn's old book,"How To Make Your Car Handle" had a formula to compute sway bar stiffness, but I could never make the math work.

Perhaps some engineer types could chime in?

BGL

vove

-good point BGL.

Tom W

Erick,

My $0.02. As you know, when I had a 25 up front (front set to full soft) and the 19 in the rear at firm, I still had significant understeer. After this weekend when I changed to middle in the front at middle in the rear (with the 22 mm rear) I achieved near neutrality. For reference I have camber at -2/-2.5, MPSC tires (205/255 x 17) run at 32/35 hot and JIC cross suspension set at 2 clicks less than full firm f and r. I was very happy with the handling after firming the front bar from full soft to the middle - it made a nice difference.

Given that it doesn't take longer than about 30 minutes to swap the bar, and you have the bar that can answer the question, why not just try it?

RSAErick

Thanks everyone. I will install the 19 mm 3-way adjustable sway bar and see how it goes.

Erick

JoeW

And be sure you post back your opinion of the results. Thanks in advance. Joe W.

Bill Gregory

FWIW, I'd probably keep the larger bar, however, as Tom pointed out, it's easy enough to change them out and compare. Clearly the adjustable bar is more useful in tuning the chassis.

pete000

I picked up a RSA front and rear sway bar and the part numbers are:

964.343.707.35 Front
964.701.07 Rear

Obviously the rear bar will not work on my car, but I am wondering if the 965 Turbo Look rear bar fits the 964 narrow body ?

I have a 19mm Tiptroinic rear bar and noticed the 965 Tiptronic is 21mm

RSAErick

During recent searches petaining to sway bars and drop links, I stumbled upon this post that I started in 2004.... 2004!!!

I'm very embarrassed that I did not follow up with the results of my sway bar experiment. Shame on me! I gain so much knowledge from all of you, and it would be nice to feel like a contributor for once, rather than the perpetual recipient of all of your expertise. So, I'm hear to make good on my long overdue duty:

I replaced the 21 mm rear sway bar (964.333.701.07) with a 3-way adjustable 19mm rear sway bar (set to full firm). The results were very noticable and positive on the track. The car went from consistent understeer to neutral handling. Except in very slow corners, where I still exhibit mild to moderate understeer. Still, it was a large improvement.

Hope that someone finds this information useful some day!

Thanks.

christallon

Erick,

My understanding is that as you ramp up to higher spring rates in the rear, a smaller rear bar is advantageous. I installed 400 lb springs in the rear of my C2 and swapped out the 21mm single bar to the 3 way 18mm RS bar set to middle setting. The car turns in very nicely. I do not notice any under-steer whatsoever. I have the 24 mm bar upfront set at 2nd hard of 5. I have considered setting the front at full hard which should make the car turn in even quicker. The front springs are 180 lbs.

The idea in the rear, using a light bar, is that all the weight is there, and the car will naturally rotate easier with a lighter bar, as long as the spring rates are up (presumably to keep the car flat). The RS cars also used heavier rear spring rates.

Ken D

We figured you'd get around to it eventually.

Steve Weiner-Rennsport Systems

Chris,

The main reason you are not experiencing any understeer is due to your 180/440 spring package,....

Tightening the front bar will make the car push more so be careful what you ask for,......

Stiffening the rear makes the car more neutral; stiffening the front increases the understeer.

Hope this helps,

christallon

Thanks Steve, much appreciated input.

If I back off on the front, 1, to the middle setting, will this make the car more prone to oversteer? I like the idea of charging to a turn under full power and lifting off the throttle and feeling the car move either right or left (turning in) slightly, just before I add steering input. The early torsion bar cars did this quite naturally. Maybe it is a weight thing...

I remember reading that the factory installed smaller rear bars, and heavier front bars the to help make the car more "rotatable", is there any truth to this?

Steve Weiner-Rennsport Systems

Yes, a little bit. I think you'd like it,...

Its the other way around. Stiffening the rear (or using a larger bar), relative to the front, makes the car more "rotatable". Remember, the suspension motion ratios are different front and rear so one cannot make direct comparisions about sizes.

In the specific case of the 964's, the factory used a wide front-to-rear spring split (with very stiff springs) to make it neutral, using the bars as a fine-tuning tool for each driver.