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Torsion-Bar Springs

Posted in How To on April 1, 2003
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Photographers: Fred Williams

We wish we could tell you that torsion-bar springs are modern technology's answer to the quest for soft riding, long travel, and easily modified suspensions. When we were researching this story we hoped that we would stumble across some tech tidbit that would open the door to some unexplored applications for these straightened-out coil springs to give you new alternatives to the leaves and coils. We're sad to say it seems we need to keep looking.

"Basic" and "off-road use" go hand-in-hand. Of all the types of springs you can find on a 4x4 the torsion bar uses the most basic design. Throw in the fact that our country's M1A1 Abrams battle tanks use torsion-bar suspension and they start to sound like the perfect spring for off-road use don't they?

Unfortunately the reality is that this simple spring design has been great for the original equipment manufacturers (OEMs), but has left us in the aftermarket with 4x4s that are more difficult and more expensive than ever to lift. For now the only correct way to lift a torsion-bar-sprung independent-suspension 4x4 is to drop all of the suspension locating points down to gain lift, sort of like adding longer shackles to leaf-spring suspensions. The upside is that when lifted this way a torsion-bar-equipped truck can maintain a stock ride quality. The down side is that it is almost impossible to get additional travel out of this kind of suspension. If you're starting to feel discouraged about owning a torsion-bar-outfitted truck, fear not! We'll keep investigating options for torsion-bar suspensions until we find something that makes them work better than the other spring options out there.

131 0306 01z+dodge ram 1500+front side view
This CAD illustration of the Hummer H2 front suspension shows the components of a typical torsion-bar suspension. To understand how a torsion spring works, imagine your chest is the crossmember, your left arm is the torsion bar, and your hand is stuck in the lower A-arm. When the suspension compresses, the torsion bar (or your arm) is twisted clockwise by the lower A-arm. But because the torsion bar is anchored at the other end in the crossmember (just as your arm is anchored in your shoulder) the torsion bar will exert a counterclockwise force to push the A-arm down and hold the truck up. This CAD illustration of the Hummer H2 front suspension shows the components of a typical torsion-bar suspension. To understand how a torsion spring works, imagine your chest is the crossmember, your left arm is the torsion bar, and your hand is stuck in the lower A-arm. When the suspension compresses, the torsion bar (or your arm) is twisted clockwise by the lower A-arm. But because the torsion bar is anchored at the other end in the crossmember (just as your arm is anchored in your shoulder) the torsion bar will exert a counterclockwise force to push the A-arm down and hold the truck up.
The beauty of a torsion-bar suspension is that all of the mass and spring stress is concentrated low and inline with the truck's frame and beefy lower A-arms. That's why torsion-bar-equipped trucks have wimpy-looking upper A-arms stamped out of steel or forged aluminum like on this Dodge. They don't need anything stronger. Torsion bars have been popular with the OEMs that offer IFS 4x4s because they keep the truck's center of gravity low, leave room for big CV-shafts, and offer the lowest potential unsprung weight of any suspension design. The beauty of a torsion-bar suspension is that all of the mass and spring stress is concentrated low and inline with the truck's frame and beefy lower A-arms. That's why torsion-bar-equipped trucks have wimpy-looking upper A-arms stamped out of steel or forged aluminum like on this Dodge. They don't need anything stronger. Torsion bars have been popular with the OEMs that offer IFS 4x4s because they keep the truck's center of gravity low, leave room for big CV-shafts, and offer the lowest potential unsprung weight of any suspension design.
Lots of people ask us if they can crank their torsion bars up to lift the front of a 4x4 without buying an expensive lift kit. The answer is yes, but doing so has its downsides and you're not going to be able to get much lift anyway. The adjuster screws are there to compensate for adding a snowplow, winch, or to restore ride height as the torsion bars relax and sag the suspension. They are not for you to crank in to get the maximum lift height possible. If you do go the poor man's lift route make sure to adjust both sides of the truck to the same height and have the front end professionally aligned afterward. Lots of people ask us if they can crank their torsion bars up to lift the front of a 4x4 without buying an expensive lift kit. The answer is yes, but doing so has its downsides and you're not going to be able to get much lift anyway. The adjuster screws are there to compensate for adding a snowplow, winch, or to restore ride height as the torsion bars relax and sag the suspension. They are not for you to crank in to get the maximum lift height possible. If you do go the poor man's lift route make sure to adjust both sides of the truck to the same height and have the front end professionally aligned afterward.
Torsion-bar suspensions do have some drawbacks. The biggest problem we see is that it is almost impossible to have a progressive-rate torsion bar. Some OEMs have compensated for this by designing the suspension to ride on jounce bumpers (don't call them bumpstops!) to effectively get a progressive spring rate at the wheel. But this still leaves the problem torsion bars have of limiting the amount of compliance that can be designed into the suspension. Compliance is a term used by suspension engineers to describe the up-and-to-the-rear path the tire should ideally take as the suspension compresses. A torsion bar will not permit this complex suspension motion without buckling the bar. Torsion-bar suspensions do have some drawbacks. The biggest problem we see is that it is almost impossible to have a progressive-rate torsion bar. Some OEMs have compensated for this by designing the suspension to ride on jounce bumpers (don't call them bumpstops!) to effectively get a progressive spring rate at the wheel. But this still leaves the problem torsion bars have of limiting the amount of compliance that can be designed into the suspension. Compliance is a term used by suspension engineers to describe the up-and-to-the-rear path the tire should ideally take as the suspension compresses. A torsion bar will not permit this complex suspension motion without buckling the bar.

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