swaybars links on LOW cars

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  • CorvallisBMW
    Long Schlong Longhammer
    • Feb 2005
    • 13039

    #1

    swaybars links on LOW cars

    Threw the GCs on the car and realized that the swaybar end links, even though they're adjustable, seem too long now. The ends of the swaybar that come out past the bushings are no longer horizontal when the car is on the ground, they actually pitch up in the front. Does this adversely effect the functionality of the swaybar? Would I be better off welding on some M3-style links?
    Last edited by CorvallisBMW; 04-11-2011, 11:21 AM.
  • z31maniac
    I waste 90% of my day here and all I got was this stupid title
    • Dec 2007
    • 17566

    #2
    I think it *technically* does since you are changing the angle of the lever, but is it going to cause a *noticeable* difference in a street driven car?

    Probably not.
    Need parts now? Need them cheap? steve@blunttech.com
    Chief Sales Officer, Midwest Division—Blunt Tech Industries

    www.gutenparts.com
    One stop shopping for NEW, USED and EURO PARTS!

    Comment

    • nando
      Moderator
      • Nov 2003
      • 34827

      #3
      it does affect the swaybar. you can get adjustable links to fix it, and/or go with front M3 style endlinks.
      Build thread

      Bimmerlabs

      Comment

      • CorvallisBMW
        Long Schlong Longhammer
        • Feb 2005
        • 13039

        #4
        the car already has the adjustable-length endlinks, but they don't go short enough to keep the bar horizontal to the ground.

        Comment

        • bimmerteck
          Mod Crazy
          • Mar 2009
          • 762

          #5
          As long as both sides' end links are set at the same length they're should be no ill effects.

          Comment

          • nando
            Moderator
            • Nov 2003
            • 34827

            #6
            Originally posted by bimmerteck
            As long as both sides' end links are set at the same length they're should be no ill effects.
            you're talking about preload. having the swaybar parallel with the ground is still important.
            Build thread

            Bimmerlabs

            Comment

            • kronus
              R3V OG
              • Apr 2008
              • 13003

              #7
              Originally posted by nando
              you're talking about preload. having the swaybar parallel with the ground is still important.
              Why? The physical behavior of the sway bar doesn't change depending on its angle relative to the ground. The only issue is directional forces on the sway bar mounts, and if Corvallis has an aftermarket sway bar, the mounts are beefed up, anyway.
              cars beep boop

              Comment

              • kronus
                R3V OG
                • Apr 2008
                • 13003

                #8
                wait, nevermind, drew some force diagrams and did the math. The ends need to be level. Nando is right.
                cars beep boop

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                • z31maniac
                  I waste 90% of my day here and all I got was this stupid title
                  • Dec 2007
                  • 17566

                  #9
                  ^Is it a big difference?

                  Just curious, irnotenjuneer
                  Need parts now? Need them cheap? steve@blunttech.com
                  Chief Sales Officer, Midwest Division—Blunt Tech Industries

                  www.gutenparts.com
                  One stop shopping for NEW, USED and EURO PARTS!

                  Comment

                  • nando
                    Moderator
                    • Nov 2003
                    • 34827

                    #10
                    Originally posted by kronus
                    Why? The physical behavior of the sway bar doesn't change depending on its angle relative to the ground. The only issue is directional forces on the sway bar mounts, and if Corvallis has an aftermarket sway bar, the mounts are beefed up, anyway.
                    it matters. do some searching.
                    Build thread

                    Bimmerlabs

                    Comment

                    • nando
                      Moderator
                      • Nov 2003
                      • 34827

                      #11
                      Originally posted by kronus
                      wait, nevermind, drew some force diagrams and did the math. The ends need to be level. Nando is right.
                      :D

                      I don't know *how* big of a difference it makes, but it's not difficult to get there, so why not? :)
                      Build thread

                      Bimmerlabs

                      Comment

                      • kronus
                        R3V OG
                        • Apr 2008
                        • 13003

                        #12
                        Originally posted by z31maniac
                        ^Is it a big difference?

                        Just curious, irnotenjuneer
                        The main difference is in the way the sway bar deforms - it is effectively a torsional spring that is being operated from two ends, so we can assume it has a fairly well-defined spring constant (commonly referred to as k, means the same thing as the "stiffness" of a sway bar, e.g. thicker bar = larger k). The effect is that n force applied to one end comes out of the other end as k*n force, which actuates the suspension in the specific way necessary to decrease body roll.

                        When the sway bar is not level, the effective torque on the torsion spring is reduced when an equivalent force is applied to one side of the suspension, due to a shorter effective level length. This means that the output torque of the other side of the torsion spring (which is the input torque multiplied by the spring constant) is reduced even further, leading to less force output on the other side of the car's suspension. The overall effect is that the sway bar is providing less anti-sway effects on the car when it is installed at a non-level angle. However, (this is the answer to your question) the decrease in effectiveness is linear with the effective lever length - the horizontal distance between the sway bar mount and the vertical location of the sway bar-end link point. You can figure the effectiveness of your sway bar mounting position by calculating the cosine of the mounting angle.

                        Example: cos(15 degrees) = ~.96, so at a 15 degree mounting angle, the sway bar is operating at 96% of its maximum anti-sway effectiveness. That's pretty good and probably not enough to worry about.

                        disclaimer - I am not a physicist or a meche, these calculations and derivations are mostly conjecture and assumption, but I think they're close to correct.
                        cars beep boop

                        Comment

                        • CorvallisBMW
                          Long Schlong Longhammer
                          • Feb 2005
                          • 13039

                          #13
                          meh, I can live with 96% :)

                          Comment

                          • kronus
                            R3V OG
                            • Apr 2008
                            • 13003

                            #14
                            Originally posted by CorvallisBMW
                            meh, I can live with 96% :)
                            The more important thing is that your end links are as close to vertical as possible. If they're angled, the sway bar mounts will get a lot more horizontal force applied to them than they're designed for.
                            cars beep boop

                            Comment

                            • Sagaris
                              R3VLimited
                              • Sep 2009
                              • 2243

                              #15
                              Don't forget that the angle of the force acting on the swaybar end-link changes as the suspension compresses.

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