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Here is some sway bar info for you..... Posted by REM in Seattle [Email]  (#4)  [Profile/Gallery]
(more from REM in Seattle) on Mon, 25 Nov 2002 10:42:47
In Reply to: Lost track of that sway bar thread and ready to get one, Ed G, Mon, 25 Nov 2002 07:39:42 Members do not see ads below this line. - Help Keep This Site Online - Signup |
NG900/9-3 – INSTALLING THE 22mm REAR SWAY BAR
By Rob Mustard (aka REM in Seattle)
Search word: rem_mod
Last updated – April 26, 2013
PREMISE
Installing a 22mm rear sway bar is probably the most significant, and cost effective, change to my 1998 900SET that I have made. The larger rear sway bar really changes the handling by getting rid of most of the body roll. The rear end feels much more connected to the car, not like it is just trailering along. Ride quality is sacrificed slightly as the larger rear sway bar does allow more road vibration to be coupled through the rear twist beam axle.
The following is the technical description of the NG900/9-3 rear axle assembly from the Saab literature:
Twist-Beam Rear Axle
“The new Saab 900 rear axle is designed to provide dynamic roll oversteer, which Saab engineers believe gives better straight-line stability and more positive turn-in control than roll understeer. This makes the Saab 900 more responsive, and at the same time more damped in its directional movements--it's a characteristic that has been a fundamental part of the Saab handling philosophy for many years.”
“The H-shaped axle side arms are of a heavy gauge metal, and additional welds reinforce the assembly. This design is lighter than its predecessor and provides more longitudinal compliance, to further improve ride comfort. The front ends of the side arms are connected to the body through large-diameter, well-tuned rubber bushings, with direct-acting compact, taper-wound coil springs. Separate gas-pressurized telescopic shock absorbers are attached behind the wheel hubs, while maintenance-free wheel bearings are mounted inside welded hub carriers.”
“For fine-tuning the roll stiffness at the rear, a separate stabilizer bar is mounted inside the open-channel cross tube of the rear axle assembly, with a second stabilizer bar bolted externally behind. Extra plates are welded to the rear axle mounts to improve lateral stiffness.”
So, the torsional stiffness of the Saab NG900/9-3 rear axle assembly is actual the sum of 3 components; the H-shaped axle weldment, the inner stabilizer (sway) bar, and the external stabilizer (sway) bar. Since only the external rear stabilizer (sway) bar is easily replaced, that is the focus of the aftermarket tuning.
The stock rear sway bar on my 1998 900SET was 15mm in diameter. The formula for torsional stress says that, all other dimensions being equal, the force from the bar is proportional to the diameter of the bar raised to the 4th power (D2/D1)4. So if the stock 15mm diameter bar is set as the baseline, an 18mm diameter bar will be 107% stiffer, a 20mm diameter will be 216% stiffer, and the 22mm diameter bar is about 363% stiffer than the stock 15mm diameter bar.
There are a couple Saabnet sponsors that carry the 22mm diameter rear sway bar for the NG900/9-3, including http://www.genuinesaab.com.
DRIVING IMPRESSIONS
I can say that the new rear sway bar is definitely felt on washboard roads or uneven pavement, like the semi-truck induced dips in the pavement on certain highway sections. The feeling is like the rear tires are over-inflated by a couple PSI, kind of a series of thumps felt in the bottom seat cushion. The tendency to understeer (the feeling that the front tires are just going to keep plowing straight ahead when you throw the car hard into a corner) is definitely reduced. The rear-end used to feel like it was just trailering behind, only slightly connected to the rest of the vehicle. Now the rear-end feels very connected to the vehicle. The sense when driving fast through corners that the front tires are being pushed to the outside of the corner by the rear ‘trailer’ wheels, is greatly diminished. The rear sway bar is not magic. The vehicle is still a Saab, still front wheel drive, and still understeers. But the understeer is more predictable and controlled than before, allowing for more confident and spirited driving in the ‘twistys’. Also I am beginning to feel that the rear sway bar upgrade will really point out the softness of the stock rubber front tracking arm bushings and the front struts when the car is pushed hard in corners.
I am now playing with the tire pressures a bit to compliment the new rear sway bar. Before the rear sway bar I was running 38 PSI in front tires and 36 PSI in the rear tires to reduce the understeer feel. As you may remember, the Saab tire pressure sticker on the driver’s door recommends for 205/50-16 tires:
32 PSI all around for 1-3 occupants and speeds up to 100MPH.
35 PSI all around for 4-5 occupants and speeds up to 100 MPH.
39 PSI all around for speeds over 100 MPH.
(Weirdly, the owners manual says 33 PSI, 36PSI, and 39 PSI respectively. Bars to PSI conversion rounding? Who knows.)
Anyway, I am now running 35 PSI all around. It seems pretty good so far. With the front pressure down from 38 PSI, I don’t feel the bumps in the road through the steering wheel as much. But I now feel the bumps in the seat of my pants a bit more. As with any suspension change, it is all a matter of trade-offs.
INSTALLATION INSTRUCTIONS
Installation of the 22mm rear sway bar is very easy, though if you live in an area where road salt is used rusted bolts could complicate things. There are basically 4 ea. 8mm bolts that go through the rear sway bar, through the rear axle, and into two nut plates on top of the axle. Just remove the 4 bolts to remove the stock sway bar. Some people report that they simply worked on the rear sway bar without lifting the car. I chose to put the rear of the car on Rhino® ramps. But then I am 6’1”, weigh 220lbs., and have a 50-inch chest; so squeezing under the car is not quite as easy for me.
The 22mm rear sway bar I bought had slightly larger holes than the stock sway bar. You can re-use the stock 8mm hardware to mount your rear sway bar, just use large thick washers under the heads of the bolts. Torque the bolts to about 20 ft-lbs.
Another option is to replace the stock hardware with 3/8” Grade 8 hardware (or 10mm hardware). According to my handy fastener guide, the 3/8” fasteners will provide 40-50% greater clamping strength than the 8mm fasteners. I used 3/8-24 by 1-1/2” long Grade 8 bolts, 3/8-24 Grade 8 nuts, with 3/8” Grade 8 washers under the bolt heads and under the nuts (total cost of 3/8” hardware, less than $5 US Dollars at the local hardware store). I also used Loctite 242 medium strength blue thread locker on the first 1/2” of bolt thread.
The holes in the 22mm rear sway bar and the Saab axle assembly were large enough to accept the 3/8” hardware. First I installed all the 3/8” fasteners loosely to allow movement for alignment of all the fasteners. Then I torqued the 3/8” fasteners to about 20 FT-LB (pretty tight with a standard 3/8” ratchet). Finally I torqued the 3/8” fasteners to 30-35 FT-LB using a torque wrench.
By very careful working around the rear brake line and rear ABS sensor cables not the damage anything while holding the nuts with a wrench.
Disclaimer
This information is a compilation from numerous sources and is provided for general information and education only. It is not intended to be and is not a substitute for professional advice. Use of any information contained herein is at your own risk and all information is provided on an "as is" basis without any representations or warranties. The reader assumes all responsibility for any problems, injuries, or damage resulting from use of this information.
->Posting last edited on Fri, 26 Apr 2013 14:09:30.
_______________________________________ REM in Seattle Current: 2013 Volvo XC60 R-Design, Rebel Blue, 3.0L 6-cyl turbo, Automatic 2024 MINI Cooper S Convertible, 2.0L 4-cyl turbo, 6-speed manual Former: 2005 Saab 9-3 Aero Convertible, Steel Gray metallic, 2.0L 4-cyl turbo, 5-speed 1998 Saab 900SET 5-door, Silver, 2.0L 4-cyl turbo, Automatic 1991 Alfa Romeo Spider convertible, Alfa Red, 2.0L 4-cyl, 5-speed 1984 Saab 900T 3-door, Red, 2.0L 4-cyl turbo, 5-speed
, Mon, 25 Nov 2002 10:42:47 <-- Viewing This Message
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