How does a sway bar work, what is it and how does it affect my vehicle’s handling?
Something that most car buyers and owners will never think about is the sway or anti-roll bar. Here’s what it does and why it’s important to the way your vehicle handles.
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 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.
What’s the point of a sway bar?
The idea of a 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 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.
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 minimise 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 minimising 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 minimising 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.
Next week we’ll look at why some off-road vehicles have the ability to disconnect their sway bar and why you would want to do that.