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How Sway Bars Work

By Dan Thompson

Earlier someone asked how sway bars work. Here's my stab at it:

Think of a bar bent into the shape of a "U". Mount this U by 2 points on its bottom, like this:

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Pull or push on both uprights of the U and it will swing toward or away from you because it will pivot on its mounting points.

In the same way a sway bar, whose "uprights" are attached to your suspension and whose "bottom" section is mounted to the body of your car by 2 bushings, will not offer any resistance to suspension travel as long as both sides are moving up or down equally.

Take this same "U" and hold one of the uprights stationary while trying to push or pull on the other. Now you'll find the bar resisting this motion. The greater the bar's torsional rigidity, the greater it's resistance to this twisting motion. Let's say that with all your strength you're able to push or pull the upright to a 90 degree angle, either toward or away from you. The farther you push the upright, the harder it gets to push it. Now instead of moving one upright while holding the other stationary, you push on one and pull on the other. One upright will be away from you at a 45 degree and one will be toward you at a 45 degree angle. The "U" is still twisted at a 90 degree total angle(45+45=90), but each leg is now only 45 degrees from its original position before the stiffness of the bar prevents any more twisting.

Applied to your car, when you go into a corner the suspension on one side compresses and the other side unloads (otherwise known as body roll). This is the same as "pushing" on one side of the bar and "pulling" on the other side. The stiffer the bar is, the greater its resistance will be to this twisting action. Therefore a stiffer bar will offer greater resistance to body roll, keeping your car flatter in the turns.

Think of a sway bar as a "helper spring" that only works when the suspension on one side of the car moves differently from the suspension on the other side of the car.