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Anti-Roll Bars: What Are Sway Bars & How They Work (Explained)

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  • 8 min read

Last Updated on: 7th September 2023, 12:39 am

Ever been in a car that leans to one side when going around a bend? That’s called body roll, it causes a car to feel “boaty”.

Anti-roll bars and sway bars will reduce this body roll and stiffen up the car. But should you fit your car with an aftermarket or upgraded anti-roll bar?

Scroll down for everything you need to know about anti-roll bars and sway bars.

anti-roll bar

What Are Anti-Roll & Sway Bars?

An anti-roll bar (also known as a roll bar, anti-sway bar, sway bar or stabilizer bar) is a crucial part of numerous vehicle suspension setups.

It helps reduce body roll while cornering or driving over road irregularities.

Anti-roll bars connect the opposing wheels through short lever arms known as ARB links or drop links linked by a metal bar or tube, which acts as a torsion spring.

Upgraded drop links goes very well with upgraded anti-roll bars.

anti-roll bar diagram

A sway bar increases a suspension’s roll stiffness.

Roll stiffness is its resistance to roll during turns, independently of the suspension spring rate or damping.

Anti-roll bars were uncommon on pre-1950 cars due to generally stiffer suspension and the acceptance of car body roll.

From around 1950 onwards, manufacturers more regularly fitted production cars with anti-roll bars.

Types of Anti-Roll Bars

OEM and aftermarket anti-roll bars come in various setups and types. Aftermarket sway bars are usually thicker than OEM ones.

Some of the most common types of anti-roll bars are listed below.

  1. Adjustable
  2. Hollow & Solid
  3. Semi-Active
  4. Active


Most aftermarket anti-roll bars are adjustable. However, some anti-roll bars are of a fixed position.

adjustable anti-roll bar

The benefit of making an anti-roll bar adjustable is the customizability of anti-roll stiffness.

Usually, adjustable sway bars have 2-3 options of roll stiffness. They do this via drilled holes at differing lengths of the bar, changing the bar’s stiffness.

Usually, the longer the bar, the less stiff it will be; the shorter the bar, the stiffer it will be. Therefore, fixing the droplinks at different points on the bar can change the roll stiffness.

Hollow & Solid

Some anti-roll bars can be solid, while others are hollow.

Solid sway bars have higher stiffness, while hollow ones have less stiffness. However, a solid bar will be heavier, which may be a consideration for you.

hollow vs solid sway bars

You can also get anti-roll bars with varying thickness.

Similarly to altering the position of the droplinks on an adjustable sway bar, altering the thickness of the bar can also change the roll stiffness.


Semi-active anti-roll bars are a feat of modern automotive engineering.

Unlike a regular anti-roll bar, which you can’t adjust on the go, a semi-active one, you can change the bar’s stiffness while moving.

Usually, a semi-active sway bar has an actuator on the drop link; altering the length of the link can change the roll-stiffness of the car.

semi active sway bar drop link

This semi-active allows you to have a higher degree of control over the vehicle’s characteristics while moving.


Active anti-roll bars are a step up from semi-active; they usually have more control over the stiffness than semi-active systems.

active anti-roll bar

By changing the anti-roll bar stiffness, active systems lessen body roll during cornering, keeping the car more level during turns while still allowing a comfortable ride over rougher surfaces.

The active stabilizer system relies on various sensors and electric motors; some cars use hydraulic systems instead.

What Do Sway Bars Do?

Anti-roll bars are primarily designed to reduce the natural tendency of vehicles to lean while cornering.

anti-roll bar before and after

The other function of an anti-roll bar is to tune the handling and balance of a car.

You can tune out understeer or oversteer behaviour by changing the proportion of the total roll stiffness from the front and rear axles.

Increasing the ratio of roll stiffness at the front of the car increases the total load transfer that the front axle reacts to, decreasing the proportion that the rear axle responds to.

This makes the outer front wheel run at a comparatively higher slip angle. The outer rear wheel runs at a comparatively lower slip angle, which is an understeer effect.

Increasing the ratio of roll stiffness at the rear axle has the opposite effect and decreases understeer.

understeer vs oversteer

How Do Anti-Roll Bars Work?

Anti-roll bars and sway bars work by connecting the two sides of a car’s suspension.

It is typically composed of a tubular steel bar, formed into a “U” shape that connects the left and right sides of the suspension.

If the left and right wheels move together, the bar will rotate around its mounting points.

If the wheels move differently, the anti-roll bar is subjected to torsion and forced to twist.

how does anti-roll bar work

Each end of the sway bar is connected to an end link (also known as a droplink, ARB link or link) via a flexible joint.

The sway bar droplink attaches to a spot near the wheel or axle, transferring the forces through the anti-roll bar to the other side of the suspension system.

Forces are transferred in the following order:

  1. From the wheel or axle
  2. To the end link via a bushing
  3. To the anti-roll bar via a flexible joint
  4. To the end link on the opposite side of the bar
  5. To the opposite wheel or axle

Upgraded Anti-Roll Bars

Upgraded anti-roll bars are usually made from a more robust material, are thicker and of higher quality.

They are also usually powder coated for better longevity and rust protection. Aftermarket sway bars are, most of the time, adjustable with different options of roll stiffness.

Upgrading an anti-roll bar usually brings enhanced handling, sometimes at the expense of ride quality and comfort.

upgraded anti roll bar

Should You Fit Uprated Anti-Roll Bars?

If you’re using the car to do the shopping or general daily driving, then fitting upgraded or stiffer anti-roll bars is probably not a wise idea.

However, if you prefer a stiff car with minimal body roll, you may benefit from a more rigid sway bar setup.

Track and racing use is where stiffer anti-roll bars work the best. Suppose you’re going to be using the car for track days or racing.

In that case, you will most likely benefit from fitting an upgraded anti-roll bar. Upgrading your suspension to a coilover or stiffer spring setup goes great with upgraded sway bars and drop links.

should you fit an anti-roll bar

Benefits & Drawbacks

The benefits and drawbacks of anti-roll bars depend on your use case or preference.

However, there are general characteristic changes between a stiffer and softer anti-roll bar that, to the vast majority, will be either an advantage or disadvantage.

Because anti-roll bars join wheels on opposite sides of the vehicle, it transmits the force of a bump on one wheel to the opposing wheel.

On rough surfaces, stiffer anti-roll bars can produce harsh, side-to-side body motions; this increases in severity when increasing the thickness and stiffness of the sway bars.

stiffer sway bar over rough surfaces

Excessive roll stiffness can cause the inside wheels to lift off the ground during hard cornering; however, this may benefit many front-wheel-drive vehicles as it limits understeer.

Benefits of stiffer or upgraded anti-roll bars:

  • If the sway bar is adjustable, it allows you to alter the roll-stiffness of the car quickly.
  • Stiffened anti-roll bars enhance handling around corners.
  • When set up right, stiffer anti-roll bars improve a cars understeer or oversteer characteristics.
  • Reduces a cars body roll which may benefit some.

Drawbacks of a stiffer or upgraded anti-roll bar:

  • A more uncomfortable ride when going over rough surfaces.
  • Stiffer anti-roll bars can make a car feel more rigid and less “boaty”, which some people prefer.
  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer. He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

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