There are two primary factors that determine an anti-sway bar’s torsional stiffness: the diameter of the bar and the length of the bar’s "moment arm" (more commonly known as the amount of leverage that the vehicle is able to apply against the twisting motion of the bar.)

Diameter is generally the easiest concept to grasp, as it is somewhat intuitive that a larger diameter bar would have greater torsional rigidity. Torsional (or twisting) motion of the bar is actually governed by the equation:

twist = (2 x torque x length)/(Pi x diam^4 x material modulus)


And since "diameter" is in the denominator, as diameter gets larger, the amount of twist gets smaller. Which, in a nutshell, means that torsional rigidity is a function of the diameter to the fourth power! This is why a very small increase in diameter makes a large increase in torsional rigidity.

To compare, for example, the rigidity of a Saab's stock rear 15mm anti-sway bar to the SAS larger 22mm bar, simply use the equation, 22^4/15^4 which yields 4.63. In other words, a 22mm bar is 4.63 times as stiff – or 363% stiffer – than a 15mm bar of the same design (with all else being equal).

So how does your double bar set-up correspond to the SAS rear bar? Obviously you have the stock rear bar in place so 100% of stock plus the Abbott anti-sway bar which is what 19mm? That would be another 2.57 times the original or another 257%, so a total of 357% of stock anti-sway bar stiffness or very close to the SAS anti-sway bar alone.




posted by 208.49.24...

• Doubled up rear swaybars on 9-3... It's now been done, Schu, Tue, 4 Sep 2001 08:02:31
  • Rear anti- way bar stiffness...., REM in Seattle, Wed, 5 Sep 2001 13:27:08 <-- Viewing This Message
    • close .., Kevin K , Wed, 5 Sep 2001 15:55:22
      • Interesting, Schu, Wed, 5 Sep 2001 18:44:34
      • Oops..I did take math once, or twice, really I did. :^) N/M, REM in Seattle, Wed, 5 Sep 2001 17:00:54
  • Checked wet conditions?, Kevin K , Tue, 4 Sep 2001 08:49:50
    • Good Input... more, Schu, Tue, 4 Sep 2001 09:08:55
      • more, Kevin K , Tue, 4 Sep 2001 11:08:25
        • More, Schu, Wed, 5 Sep 2001 07:34:31
          • sway bar?, Kevin K , Wed, 5 Sep 2001 10:05:15
            • Re: sway bar?, Schu, Wed, 5 Sep 2001 10:32:45
              • Re: sway bar?, Kevin K , Wed, 5 Sep 2001 11:07:55

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