The front suspension of an Alfa Romeo Alfetta, with the anti-roll bar highlighted in red. Photo: Evan Mason
An anti-roll bar or sway bar, as the name suggests, prevents your car from rolling about in the corners like a boat on the high seas.
If you’re someone who likes to bring your car out for a trackday, you’ll enjoy the benefits a stiff anti-roll bar brings.
All cars are fitted with an anti-roll bar, which keeps your tyres connected to the road and stops your passengers getting sick.
What is an anti-roll bar?
The anti-roll bar itself is a simple piece of engineering.
It’s essentially a U-shaped cylindrical piece of metal that connects both the left and right ends of an axle.
When you round a corner, the mass of your car shifts to the outside of the turn due to centrifugal force, causing the car to “roll”.
That is undesirable for both car control and passenger comfort, and more roll means the car takes longer to respond to your commands.
By connecting both ends, the anti-roll bar forces both ends of the axle – the wheels in this case – to raise or lower to a similar height, preventing roll.
The bar resists twisting, or torsion, through its torsional rigidity. The stiffer the bar, the less the car leans in turns.
This is why some aftermarket sway bars are made stiffer through either using strong materials or enlarging its diameter for better handling and performance.
One benefit of such bars is that the vehicle can be made to lean less without increasing the stiffness of the suspension, which compromises ride quality.
Some bars are even adjustable via the positions of the mounting position of the bar to the endlinks, or through a computer-controlled setup.
If you remove the anti-roll bar, the vehicle’s wheels can have much larger articulation, which is why you hear people who frequently off-road to “disconnect the anti-roll bar” when rock-crawling.
Disadvantages of sway bars
The drawbacks of a stiffer sway bar are that the force of the bump on one wheel will be transferred over to the other, causing very jarring movements.
On rough roads, this can exacerbate matters by making the car shake and rattle to the detriment of everybody inside it.
As mentioned above, adjustable sway bars are beneficial in this situation, allowing the driver to soften the ride.
