swaybars links on LOW cars

[CorvallisBMW]

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?

[z31maniac]

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.

[nando]

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

[CorvallisBMW]

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

[bimmerteck]

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

[nando]

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.

[kronus]

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.

[kronus]

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

[z31maniac]

^Is it a big difference?

Just curious, irnotenjuneer

[nando]

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.

[nando]

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? :)

[kronus]

^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.

[CorvallisBMW]

meh, I can live with 96% :)

[kronus]

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.

[Sagaris]

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