TORSION BARS

In some front suspension systems, torsion bars replace the coil springs. However, instead of compressing like coil springs, a torsion bar twists during wheel jounce and straightens out to its original position during wheel rebound. A torsion bar is capable of storing a higher maximum energy compared to a loaded coil or leaf spring.

One end of a torsion bar - made of heat-treated alloy spring steel - is attached to the vehicle frame. The other end is attached to the lower control arm. When the wheel moves up and down, the lower control arm is raised and lowered. This twists the torsion bar, which causes it to absorb road shocks. The bar's natural resistance to twisting quickly restores it to its original position, returning the wheel to the road.

During the manufacturing process, torsion bars are prestressed to provide fatigue strength. Because of directional prestressing, torsion bars are directional. Torsion bars are marked right of left, and they must be installed on the appropriate side of the vehicle. Left and right on a vehicle is always viewed from the driver's seat.

Torsion bars have a riding height adjustment screw at the end where they are attached to the frame.

Many late-model pickups and SUVs use longitudinal torsion bars in their front suspensions. They are used in this type vehicle because they require less space compared to coil or leaf springs. They can also be mounted low and out of the way of the driveline components. Transversely mounted torsion bars were used in some front suspensions on older cars.

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STABILIZER BARS

A variety of devices are added to basic suspension components to provide additional stability. One of the most common in the sway bar, which is also known as the anti-sway or stabilizer bar. This is a metal rod running between the opposite lower control arms. As the suspension at one wheel responds to the road surface, the sway bar transfers a similar movement to the suspension at the other wheel. For example, if the right wheel is drawn down by a dip in the road, the sway bar creates a downward draw on the left wheel as well. This produces a more level ride, and sway or lean during cornering is also reduced.

If both wheels go into a jounce, the sway bar simply rotates in its insulator bushings. It is a different matter when only one wheel goes into jounce. The stabilizer bar twists, just like a torsion bar, to lift the frame and the opposite suspension arm. This action reduces body roll.

The sway bar can be one-piece, U-shaped rod fastened directly into the control arms with rubber bushings, or it can be attached to each control arm by a separate sway bar link. The arm is held to the links with nuts and rubber bushings and is also mounted to the frame in the center with rubber bushings. If the sway bar is too large, it causes the vehicle to wander. If it is too small, it has little effect on stability.

On suspensions that use single-housing lower control arms instead of wishbone types, the sway bar can also be used to add lateral stability to the control arm. Strut rods are used on models that do not use the sway bar for this purpose. Strut rods are attached to the control arm and frame with bushings, allowing the arm a limited amount of forward and backward movement. Strut rods are directly affected by braking forces and road shocks, and their failure can quickly lead to failure of the entire suspension system.