What Does A Sway Bar Do?

A sway bar (also called an anti-sway bar or anti-roll bar) is a component of some vehicles’ suspensions. You might guess that “sway” in a car or truck isn’t a good thing, so an anti-sway bar would be useful, and in the broadest terms that’s correct. But it’s also a bit more complicated than that.

The purpose of a sway bar
The answer goes back to that guess above, that a sway (or actually anti-sway) bar tends to keep the car from swaying (or more precisely, from leaning to one side or the other). That is what a sway bar does: prevent body lean. A sway bar does nothing at all unless the vehicle is inclined to lean to one side, but when it does start to lean (which usually means the vehicle is turning — every car or truck tends to lean to the outside of a turn), the sway bar applies force to the suspension on each side, upward on one side and downward on the other, that tends to resist the leaning.

How a sway bar works
Every sway bar is a torsion spring — a piece of metal that resists twisting force. The sway bar is attached at each end, one end to one wheel and at the other end to the opposite wheel (both fronts or both rears) so that in order for the wheel on one side to be higher than that on the other the bar has to twist. The sway bar resists that twist, tending to restore the wheels to the same height, and the vehicle to level. That’s why a sway bar does nothing unless the body of a vehicle leans to one side: if both wheels rise (as they would when the vehicle hits a bump) or fall (as at a dip) at the same time, the sway bar doesn’t have to twist, so it has no effect. 

(YourMechanic).