Too often we hear the local workshop, and many 4WD and suspension people, say " Yeah mate! We can crank the bars up 2 inches" when discussing lifting a 4WD fitted with front torsion bars.

While the practise may have merit in some situations, there can be a number of unexpected consequences when lifting a set-up of this type. Many 4WD owners may find it helpful to be 'armed' with the right information before they make their purchase decision.

The torsion bar suspension in an example of an independent front suspension (IFS). With a torsion bar design, there are no leaf or coil springs; just a spring steel rod, fixed to the suspension arms at the front and fixed to the chassis back near the firewall. Torsion bars perform the same function as a coil or leaf spring. They support the vehicle's weight and absorb the movement caused by changes in the distance between the vehicle and the terrain.

An amount of twist,or tension, is placed on the bars just by  holding up the weight of the vehicle. When the terrain of the road causes the wheels to be pushed up or down, the torsion bars twist in the direction necessary to allow this movement . As the wheels return to their normal position the bars "unravel".

The resistance the torsion bar offers during this ravel/ unravel action is how the spring action is provided.

As the name of its suspension type suggests, each wheel is free to move 'independently' of each other. This, generally, allows for excellent ride and handling characteristics.For hard-core off-road enthusiasts, the torsion bar suspension design has some real disadvantages. These include limited available wheel-travel, by comparison to a solid axle design, and the difficulty in raising the suspension successfully.

At the rear of the torsion bar is a bolt and lever system that is designed specifically to control the ride height. Straight from the factory, the bolt is adjusted approximatley to the middle or center of the vehicle's range of suspension travel. (ie. the wheels can move the same distance up as they can droop down). To adjust the ride height, one only needs to tighten the adjustment bolt, which forces the lever down, twisting the torsion bar clockwise on the right side of the vehicle, and counter clock wise on the left hand side.. This action  forces the upper control arms downwards. It is this 'push-down' affect on the upper control arms which then raises or 'pushes' the vehicle higher. Simple.

Usually when you apply a 'suspension lift', the entire range of travel is moved down away from its chassis or frame. With the torsion bar system, you are really only adjusting the ride height. This is where it pays to be "in- the-know".

The range of available travel is determined by the distance between the bump-stops. The gap between the upper set of bump-stops determines the available downward travel. The gap between the lower bump-stops relates to the upward travel on the wheel. If you check the distance between the upper bump-stops at factory spec, you'll notice that the distance here is often not much greater than two finger spaces. If you adjust your torsion bars, which forces the upper control arms down to raise the vehicle. The gap between the upper bump-stops becomes even more tightly-closed  together. This action greatly affects the amount the front wheels can 'droop' from the normal rest height.

Downward wheel travel, is arguably the most important factor in determining whether a vehicle gets stuck, or pushes on in rough terrain. This is because as one of the wheels loses contact with the ground, the other side stops driving and, unless you can have  a front diff locker installed, you will only have the traction of the rear wheels to push you along- providing they  have firm contact with the ground.

In addition to this, there is a point at which the increase in adjustment pushes the front wheel alignment outside of a correctable range - which can result in erratic steering and abnormal wear on the front tyres and steering components.

Also, if you are going to adjust the original bars, rather than replace them with heavy duty ones, you could experience   ride harshness. This is because the stock bars will be tensioned to ( or almost to ) their limit and therefore they will lack the ability to act as a spring.

These factors may have you thinking it might be all too much. But, before  you decide to trade your torsion bar vehicle in on something else, you may find these tips  helpful.

- Most torsion-bar vehicles can be raised up to 25mm before any real compromise in downward wheel-travel or ride-quality is experienced.

-For 25mm-50mm of adjustment, the fitment of new heavy-duty torsion bars will counter-act against the loss of shock absorption qualities, as the new spring rate requires less adjustment to hold the vehicle weight.

-On some vehicles, the benefits of the increase in height, may out-way the disadvantage of the decrease in available downward wheel travel. But, as one of our customers said to us, while purchasing a pair of heavy-duty torsion bars, " The thing has no real wheel-travel anyway, so, why not have the height and then the ability to fit larger tyres for an even greater increase in ground clearance".

This could be a fair comment for some  applications. But wheel-travel and flexibility is not only a essential feature for off-road capability, it is also necessary for the comfort of the driver and passengers.  

NOTE: This article is an extract from Auto Alliance's web site at www.rancho.com.au 

 These pages were last updated on 4 Sep 2002.
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