When we talk about how many springs our vehicle has we generally think of the answer being four. All too often what we refer to as the 5th & 6th springs are overlooked, this being the sway bars or also known as torsion bars or anti roll bars.
Primarily the purpose of these springs is exactly that, to provide resistance to movement by way of torsional stiffness. Although they provide a similar purpose as the suspension coil springs the anti-roll bars achieve this in a slightly different manner.
Although the operation of these 5th & 6th springs is misunderstood on a regular basis their operation is really very simple. Although there are various differing design styles from torsion bars mounted in beam axles, to beam axles themselves, in this article we will take a look at the most conventional system.
Looking at the anti-roll bar itself alone, it is primarily a very simple unit and effectively makes up a “U” shape one way or the other albeit with additional bends to form the function of clearance around various components. There are intricacies within the anti-roll bar that can form the anti-roll bar to react differently but for the sake of not complicating the explanation we will just look at the bar in its most simplistic form.
To this “U” shaped bar we then have to provide some form of mounting to not only support the anti-roll bar to the chassis of the vehicle but also allow some form of rotation as the suspension transverses upward and downward. The outer points of the “U” shaped bar is then mounted to each suspension unit whether it be onto the suspension arm or shock absorber/damper housings, etc.
So now if we visualise the anti-roll bars operation for a minute we can now see if we rotate both of the suspension arms upward or downward equally where the outer mounting points are the anti-roll bar would essential happily rotate in these chassis pivot mounts freely without providing any form of resistance to the movement, the same as rotating a steel rod back and forth in two bearing housings.
Now if we fix one of the outer “U” mounting points where the link mounts to the suspension arm or shock absorber/damper housing and try to rotate the other mounting point we are met with resistance, the anti-roll bar arm is not going to want to move upward or downward easily at all due to the torsional stiffness within the steel and this is how we get our 5th & 6th springs. Essentially we apply an effort to one side and we get an opposing effort returned, which is just like our suspension coil springs, we compress and the energy built up in the spring resists and wants to release that energy and return to its former position.
So now we have our 5th & 6th springs, like suspension coil springs we can increase or decrease the torsional stiffness within the anti-roll bars to manipulate the roll stiffness behaviour of the vehicle during cornering, and as we have discovered the anti-roll bar provides absolutely zero torsional stiffness when the chassis or suspension moves up and downward equally.
Now we have a basic understanding of the fundamental on how the anti-roll bar is tasked to operate, there is essentially three ways to increase or decrease the torsional stiffness of this component, the first being what the material composition the anti-roll bar is made from.
This is easy to relate to by thinking about the structure of a piece of plastic and steel rod, for obvious reasons the steel rod will be stronger and have a higher degree of resistance to yield and breakage than the plastic rod due to its chemical composition and likewise the processing and chemical composition of steel can determine the materials inherent strength and durability.
The second factor which is quite obvious is the diameter. If we think about the diameter of a paper clip and a quarter inch piece of steel rod bent into a “U” shape and rotate each end it is clearly obvious the quarter inch steel rod provides much more resistance to bending or movement than the paper clip would giving us our second factor of torsional stiffness.
The third being leverage, this ones really simple, imagine standing on the end of a long diving board and look at how much the board flexes and sinks with your weight. Shorten the length of the diving board and it doesn’t flex as much with the same weight applied, same principal applies to the anti-roll bar, the shorter the lever arm the more effort required to rotate or deflect the arm and thus an increase in roll stiffness occurs...
So armed with this knowledge if we want to resist the effects of body roll in the front or rear we can effectively increase the roll stiffness by increasing the torsional stiffness of the anti-roll bar and likewise decreasing it to reduce the effects. By adding adjustment holes to the anti-roll bar this effectively allows us to tune the amount of roll stiffness to some degree by changing the lever arm length, (much like the diving board albeit on a smaller scale) and thus altering the torsional stiffness of the anti-roll bar. It is especially important to have this degree of adjustment due to varying degrees of handling set up that will be required and such items like the frictional resistance of the tires can play a huge part in altering the roll stiffness balance.
So we now know if we want to increase the cornering stiffness on the rear we can then add a larger rear anti-roll bar and the same applies with the front.
So is there a point where you can increase the roll resistance too much?
Absolutely, it’s all about working the tire to its maximum potential during cornering but maintaining suspension compliance at the same time, we are trying to allow the tire to generate the most amount of lateral acceleration it can before it overcomes its grip coefficient of the tire. Apply to much roll stiffness and the tire is overcome quickly before the tire has a chance to build that lateral acceleration through grip, so it’s all about finding that ‘fine-tuned’ balance specific to every applications setup.
How do these 5th & 6th springs relate with Whiteline Lowering Springs?
The anti-roll bars are designed to be an ultimate effective entry level suspension upgrade handling package tuned to suit each and every vehicle application as required. The anti-roll bars are engineered around the specific spring rates provided and ride heights developed for the Whiteline Spring kits which complement the handling balance of the vehicle nicely.