Torsion Spring: How Does Torsion Bar Suspension Work?

This brief article will highlight what a torsion bar is, how it works, its pros, and its cons. Before answering the question “how does torsion bar suspension work?” it is important to define what a torsion bar is first.

A torsion bar suspension is a type of vehicle suspension that utilizes a torsion bar as the major load-bearing component of a suspension rather than a helical coil spring. The torsion bar suspension can be described as a double wishbone design suspension variation. This is especially true since it utilizes the same fundamentals.

How Does Torsion Bar Suspension Work?

By design, the torsion bar is simply a long rod capable of twisting and resisting the vertical suspension movement. This gives the torsion suspension its unique vertical spring rate. In certain instances, the torsion bar’s end that attaches to the body is splined. One part of the torsion bar is then connected to the vehicle’s chassis.

This section will highlight the various components of a torsion bar suspension. While each car’s design and use of the torsion bar suspension will differ, the majority of vehicles on the road today utilize the following components:

  • Torsion bar
  • Lower control arm
  • Adjusting suspension arm
  • Adjusting suspension arm support
  • Bushing for the adjusting arm

On most vehicles, you can find the mounting location on the chassis on the vehicle’s transmission mount cross-member. The mount crossmember is typically a hexagonal hole that fits the torsion bar’s bolt head.

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The opposite side of the torsion bar leads to a lever, which is then bolted onto a splined slot in the vehicle suspension lower arm control.

The lower control arm has a chassis attachment point that resembles a hinge. It is connected to the torsion bar on its axis but also in line with the same torsion bar. This means the lower control arm can rotate on its hinge when a tire moves down and up. This motion, in turn, twists the torsion bar.

The torsion bar suspension can achieve stiffness by transforming the torsion bar’s resistance to the twist action into vertical resistance at the point where it meets the wheel. This is done by utilizing the lower control arm as a lever.

Compared to a coil spring suspension with a fixed installation, the torsion key needs to be altered to ensure the car’s cornering ride height is varied. This means it has the right amount of body roll stiffness when the car goes through corners.

Furthermore, the chassis anchoring point near the lever is known as the anchor arm. The anchor aims to be moved down or up by loosening or tightening an adjusting bolt. A torsion bar’s spring rate correlates to the torsion bar’s overall length, diameter, and the material that composes it.

What Are the Pros of a Torsion Bar Suspension?

Torsion Bar Suspension Has a Packaging Advantage

For improved articulation, certain cars with a front double-wishbone suspension require a taller ride height. Nevertheless, there are limits to how high the vehicle’s ride height can be due to the prospective interference between the coil spring and the upper control arm in an excessive rebound.

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This issue can be eliminated by simply switching out the coil spring for the torsion bar front suspension.

Ride Height Adjustment Is Made Easier

One of the most significant advantages of torsion bar suspension is how easy it is to adjust a vehicle’s ride height. The torsion bar’s spline is designed to enable the chassis end to be rotationally adjusted without damaging or uninstalling the knuckle ball joints or wishbone mountings.

What Are the Cons of a Torsion Bar Suspension?

Packaging

The torsion bar is long and does take up quite a bit of space alongside the chassis. This means that it is better suited to an SUV or other body-over-chassis types of cars. This means that the torsion bar isn’t suited to small wheelbase vehicles.

Maintenance

The torsion bar’s lower control arm and spline mechanism must be regularly lubricated or greased. This is in contrast to the coil spring, which doesn’t require this type of maintenance.

Bump Stop Durability

Since the torsion bar’s stiffness is linear, it isn’t as progressive as coil springs which can be altered to behave progressively. This phenomenon results in the torsion bar suspension bump stopping more often, causing it to hit harder than a coil spring suspension.

For this reason, the bump stops on the torsion bar suspension would have to be redesigned to be heavier, offering a lot more durability.

Conclusion

Torsion bar suspension can be defined as the precursor to the coil spring suspension system; however, they differ. The torsion bar suspension is used in certain vehicles, such as early racing prototype vehicles developed by:

  • Ferdinand Porsche, light-duty four-wheel drive
  • SUVs and trucks created by GMC: Chevrolet Silverado, GMC Sierra
  • Mazda B-Series
  • Ford Ranger Four-Wheel Drive vehicles created between 1988 to 2012
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