Depending on the age of your classic car the use of a sway bar was considered an option that many owners did not take especially if they planned on using the car only in a straight line, or simply did not understand the reasoning behind the need for a sway bar.
Stabilizer bars are part of a car’s suspension system. They are sometimes also called anti-sway bars or anti-roll bars. Their purpose in life is to try to keep the car’s body from “rolling” in a sharp turn.
Most vehicles these days have a sway bar and some even have two, although it should really be called an anti-sway or anti-roll bar. See, unlike its name suggests, a car sway bar is there to keep your vehicle from leaning/rolling over in corners. You’ll have noticed that sensation in your vehicle when you turn into a corner, especially at a higher speed, and the body will lean or roll to the outside and away from the corner as the vehicle is driven around it. The idea of a sway bar is that a twisting force is applied to counter that lean by applying a force to the other side of the vehicle and level it out, reducing the amount of body roll.
Think about what happens to a car in a sharp turn. If you are inside the car, you know that your body gets pulled toward the outside of the turn. The same thing is happening to all the parts of the car. So, the part of the car on the outside of the turn gets pushed down toward the road and the part of the car on the inside of the turn rises. In other words, the body of the car “rolls” 10 or 20 or 30 degrees toward the outside of the turn. If you take a turn fast enough, the tires on the inside of the turn rise off the road and the car flip over.
Roll is bad. It tends to put more weight on the outside tires and less weigh on the inside tires, reducing traction. It also messes up steering. What you would like is for the body of the car to remain flat through a turn so that the weight stays distributed evenly on all four tires.
What’s the point of a sway bar?
The idea of a car sway bar, which is connected to either both front or both rear wheels (some cars have one at the front, some have one at the rear and performance vehicles tend to have one at the front and rear) is that it resists the vehicle’s tendency to roll as it corners, thus helping to keep weight on the inside wheels as the vehicle corners improving grip and cornering control.
Note that a car sway bar only works when one wheel is either higher or lower than the other; it’s aim is to try and keep things level. And this is great for performance and road cars but it’s not always ideal for 4x4s which when you’re off-road will want as much wheel travel as possible. Obviously, the whole point of a sway bar is to try and maintain an even weight distribution from one side to the other.
A sway bar tries to keep the car’s body flat by moving force from one side of the body to another. To picture how a stabilizer bar works, imagine a metal rod that is an inch or two (2 to 5 cm) in diameter. If your front tires are 5 feet (1.6 meters) apart, make the rod about 4 feet long. Attach the rod to the frame of the car in front of the front tires, but attach it with bushings in such a way that it can rotate. Now attach arms from the rod to the front suspension member on both sides.
When you go into a turn now, the front suspension member of the outside of the turn gets pushed upward. The arm of the sway bar gets pushed upward, and this applies torsion to the rod. The torsion them moves the arm at the other end of the rod, and this causes the suspension on the other side of the car to compress as well. The car’s body tends to stay flat in the turn.
If you don’t have a car sway bar, you tend to have a lot of trouble with body roll in a turn. If you have too much sway bar, you tend to lose independence between the suspension members on both sides of the car. When one wheel hits a bump, the sway bar transmits the bump to the other side of the car as well, which is not what you want. The ideal is to find a setting that reduces body roll but does not hurt the independence of the tires.
The knock on of this is that you can use a sway bar at the front or the back, or both together, to reduce under and oversteer. For instance, to try and minimize understeer, say, on a front- or all-wheel drive vehicle (which are generally more prone to understeer than a rear-wheel drive vehicle) you could install a rear sway bar or replace the existing rear sway bar if there’s one fitted with a stiffer one via the aftermarket. Or you could remove the front sway bar or replace the existing one with a less stiff one. And the same goes for minimizing oversteer, you could fit a front-mounted sway bar or, again, replace the existing sway bar with a stiffer (thicker) one. Or remove the rear sway bar or replace the existing one with a less stiff (thinner) bar. Some performance vehicles offer adjustable sway bars to either stiffen or soften them depending on what you’re after; adjustable sway bars are available via the aftermarket too.
How does a sway bar work?
A sway bar works by resisting the twisting force applied to it when one wheel moves down or up compared with the other wheel and weight transfers from one side of the vehicle to the other – when you’re turning a corner, for instance. And, in that resistance, the bar tries to keep the wheels as level as possible. The sway bar connects your vehicle’s suspension components (one side of the vehicle to the other) and is mounted to the suspension control arms. It’s worth noting that sway bars run through bushings to ensure they don’t move up and down and can only twist.
So, as the vehicle turns a corner and weight moves from one side to the other (in the case of a right-hand turn the vehicle rolls over to the right. As the wheel begins to move up towards the body, the sway bar twists which forces the weight to transfer back across to the other side of the vehicle. The result of this action is that the vehicle begins to level out, thus minimizing the roll action when cornering.
Obviously, there are other elements working here, like the other suspension components and the intention of the engineers when they tuned the vehicle’s ride and handling characteristics. And there will usually be a difference between the ‘stiffness’ of the sway bar on the front and rear axles.
And this is important to remember because generally car makers are looking for a compromise between comfort and performance. Go too stiff (or thick) with a sway bar and when one wheel hits a bump the sway bar will try and resist the wheel movement (up or down) resulting in the vehicle feeling too firm and uncomfortable. And, depending on how the rest of the suspension has been tuned, could even see the vehicle buck off the bump.
Finally
If you own a vintage car adding a sway bar may or may not be an easy addition depending on if the car was originally designed to have them used as an option, or a kit has been designed for your specific classic car. The important part of any installation is knowing the correct size and configuration sway bar for your classic car
