Toyota Hilux Rear Anti Roll Bar/Sway Bar

By Jackson - November 15, 2016

An anti roll bar (anti-sway bar, sway bar, stabilizer bar) is a part of many automobile suspensions that helps reduce the body roll of a vehicle during fast cornering or over road irregularities. It connects opposite (left/right) wheels together through short lever arms linked by a torsion spring. A sway bar increases the suspension's roll stiffness - its resistance to roll in turns, independent of its spring rate in the vertical direction.

An anti-sway or anti-roll bar is intended to force each side of the vehicle to lower, or rise, to similar heights, to reduce the sideways tilting (roll) of the vehicle on curves, sharp corners, or large bumps. With the bar removed, a vehicle's wheels can tilt away by much larger distances

(as shown by the SUV image above).

Although there are many variations in design, a common function is to force the opposite wheel's shock absorber, spring or suspension rod to lower, or rise to a similar level as the other wheel. In a fast turn, a vehicle tends to drop closer onto the outer wheels, and the sway bar soon forces the opposite wheel to also get closer to the vehicle. As a result, the vehicle tends to "hug" the road closer in a fast turn, where all wheels are closer to the body. After the fast turn, then the downward pressure is reduced, and the paired wheels can return to their normal height against the vehicle, kept at similar levels by the connecting sway bar.

Anti-roll bars provide two main functions. The first function is the reduction of the body lean. The reduction of body lean is dependent on the total roll stiffness of the vehicle. Increasing the total roll stiffness of a vehicle does not change the steady state total load (weight) transfer from the inside wheels to the outside wheels, it only reduces body lean.

The other function of the anti-rolls bars is to tune the handling balance of a car. Understeer or oversteer behavior can be tuned out by changing the proportion of the total roll stiffness that comes from the front and rear axles. Increasing the proportion of roll stiffness at the front increases the proportion of the total load transfer that the front axle reacts to - and decreases the proportion that the rear axle reacts to. In general, this makes the outer front wheel run at a comparatively higher slip angle, and the outer rear wheel to run at a comparatively lower slip angle, which is an understeer effect. Increasing the proportion of roll stiffness at the rear axle has the opposite effect and decreases understeer.

Usual 'space arm' that most people misunderstood as anti-roll bar/sway bar.

Such design have extra pivoting point which REDUCEs the holding effect of the bar thus NOT effective as an anti-roll bar/sway bar.