How does Sway Bar work? | What is an Anti-roll Bar?

A sway bar ( also known as a roll bar, stabilizer bar, anti-sway bar, or anti-roll bar) is a most important part of the vehicle suspension system. It assists in decreasing the body roll of a car during a fast turn. An anti-roll bar or sway bar links the left and right wheels through short lever arms connected via a torsion spring. It also helps to ensure the safety of the passengers on bumpy roads. This article mainly explains the types, function, and some other aspects of the sway bar.  

What is a Sway Bar?

A sway bar or anti-roll bar is a part of the vehicle suspension system that links the opposite (right/left) sides of both rear or front suspension. It reduces the vehicle’s body tilt during a quick turn. It is a durable piece of tubular steel.

The sway bar link is a connector that connects the outer end of the sway bar to the suspension system which helps to hold the control arms of the wheels. The length of these bars is between 4 to 6 inches but may vary according to the type of vehicle. These links are connected at a 90° angle to the anti-roll bar. Maximum vehicles have small ball joints on either end of these links.

sway bar

The main function of the sway bar link is to stop excessive roll of the vehicle body and stabilize the vehicle when turning. Most cars have two anti-roll bars:

  1. One anti-roll bar on the front suspension
  2. Another anti-roll bar on the rear suspension

Some special types of cars contain only one anti-roll bar in the front suspension. The sports car contains a thick sway bar for efficient stability when turning.

A rubber bushing is installed to connect the anti-roll bar or sway bar with the body or midframe of the vehicle. The outer edge of this bar connects to the vehicle’s suspension component that holds the wheels (control arms or struts).

Working of Sway Bar

The sway bar is also known as a stabilizer bar. The anti-roll bars or sway bars are used to prevent the car from rolling over. This bar connects to each front wheel of the vehicle. This is a U-shaped steel bar.  

sway bar working

During driving, as you turn your car, the vehicle weight or body transfers to one side. As the body moves to one side, the car experiences a “sway” or “roll .”In such conditions, the anti-roll bar controls the suspension of each wheel to compensate for the car body roll, making the car more level and easier to control.

When you turn the car, the car body sways or rolls to the outside of the turn. This transfers much of the vehicle’s weight to the outer wheel, where the suspension on the two outer wheels is compressed.

During this turn, the wheels on the inside of the turn go up, or the suspension on the inner wheels extends.  

Let’s explain with a simple example, when you take a quick turn, your body deflects or moves out of the corner. At the next corner, think about how your body feels when you’re swaying, and your car experiences the same thing.

The anti-roll bar is responsible for controlling this body roll. It pushes the tires on the inner side of the turndown and compresses the suspension of the inner wheels to maintain contact with the road and handle the stability of the vehicle.

The sway bar equally distributes the weight of the vehicle across all four tires to keep the vehicle as steady as possible when cornering.

Function of Anti-roll Bar

The stabilizer bar or sway bar serves the following two major functions:

  1. The very first function of the anti-roll bar is to reduce the lean of the vehicle body. The reduction in body roll or lean depends on the vehicle’ overall roll stiffness. An increase in the vehicle’s overall lean stiffness doesn’t vary the overall steady-state weight (load) transfer from the inner wheel to the outer wheel; it only decreases body roll. The width of the track and the height of the center of gravity are used to determine the total lateral weight transfer.
  2. Another function of the sway bar is to adjust the vehicle’s driving balance. The oversteer or understeer phenomena can be adjusted by changing the overall roll stiffness ratio of the rear axle and front axle. An increase in the roll stiffness ratio at the front wheel increases the overall load shift ratio to which the front axle is responsive and reduces the rear axle’s responsiveness ratio. In general, this causes the outside front wheels to turn with a relatively high slip angle and the outside rear wheels with a relatively low slip angle. An increase in the rear axle roll stiffness ratio produces the opposite effect and reduces understeer.

Why do we need Sway Bars?

The stabilizer bars ensure safety due to that they are most commonly used in vehicles. This bar may be hazardous if the car overturns too much in turn.

It also helps to prevent the vehicle from skidding in the cornering. As a result, sway bars prevent the wheels from losing traction, which may lead the driver to skid. This makes the vehicle more difficult to control, especially when braking or cornering.

However, there are many disadvantages of the anti-roll bars due to that they don’t apply to all vehicles. A high rigid anti-roll is one of the main symptoms of a bad anti-roll bar link. This makes the whole vehicle to feel rigid when moving over bumps. If it’s too stiff, the bike is more likely to hang up.

The stiffer anti-roll bars are most commonly used on vehicles (such as race cars and high-performance sports cars like the Dodge Charger or Ford Mustang) that can encounter high steering forces on a flat road.

These cars are designed to run at high speeds on flat roads. Therefore, they have thicker front and rear bars. As a result, stiffer anti-roll bars allow these cars to make sharp turns, reducing the risk of the vehicle losing grip on the road and becoming airborne.

Types of Sway Bars

The sway bar has the following major types:

  1. Solid Bar
  2. Hollow Bar
  3. Splined Bar
  4. Active Bar

1) Solid Anti-roll Bar

This is one of the most famous types of anti-roll bars. It is a solid metal U-shaped bar that links one wheel to the opposite side wheel on the same axle. These sway bars are most commonly used in the latest vehicles.

Solid Sway Bar, solid anti-roll bar

These bars have more weight than other types of anti-roll bars. However, they have high durability and long service life.

2) Hollow Sway Bar

These bars have a very similar design to solid anti-roll bars. The main difference is that the inner side of the hollow sway bar is hollow. These bars have a long service life and high performance.

Hollow Sway Bars

They are more expensive than solid bars. However, they have low weight and high durability. They’re very popular in high-performance cars.

3) Splined Sway Bar

These are straight bars. The internal area of the splined sway bar is solid or hollow. It works similarly to the traditional bar, but it rotates directly on the connecting arm.

Splined Sway Bars

The splined sway bars are most commonly used for racing and high-performance cars. It’s easy to set up so you can adjust the track car for the course you are racing that day.

4) Active Anti-Roll Bar

The active anti-roll bar system is an electronic system. The engine control unit (ECU) regulates the performance of this system. The computer of the ECU uses actuators and sensors to change the suspension system of the car when turning.

This bar has the lowest weight and higher performance than other types of sway bars. They are most commonly used for high-end vehicles.

Sway Bar Installation Cost

The installation cost of the anti-roll bar or sway bar varies according to the area where you live and the type of bar brand. The average sway bar link replacement cost is from $120 to $180. In this cost, the cost of the labor is from $45 to $75, while the link itself costs from $75 to $95.  

Labor Cost$45 to $75
Link Cost$75 to $95
Sway Bar Link Replacement Cost$120 to $180

Advantages and Disadvantages of Anti-roll Bar

Advantages of Anti-roll Bar

  1. They ensure the comfort and safety of the vehicle passengers.
  2. The anti-roll bar can adjust vehicle dynamics such as oversteer and understeer by shifting weight to various parts of the suspension as the car steers a turn.
  3. This bar connects both ends of the vehicle suspension (left and right) with attachment points, usually through the lower arm and frame (chassis), and rotates to limit body roll in turns.

Disadvantages of Anti-roll Bar

The sway bar links the opposite side wheels of the vehicle so that it can transfer the force of an impact from one wheel to the other wheel. On broken or rough surfaces, the bar may produce more violent body movement (a “waddling” feeling); due to that, the diameter and stiffness of the anti-roll bar increase.

The disadvantage of rigid anti-roll bars is that the force hitting one wheel is transferred to the other wheel, resulting in very awkward movements. On rough roads, this can cause the car to shake or rattle, injuring car passengers and making the problem worse.

FAQ Section

What is a Sway Bar Link?

The part that links the outer edge of the anti-roll bar to the suspension system is known as a sway bar link.

What is the function of the sway bar link?

The main function of the sway bar link is to stop excessive roll of the vehicle body and stabilize the vehicle when turning.

What are the types of Anti-roll Bars?

The anti-roll bars have the following major types:

  1. Active Anti-Roll Bar
  2. Solid Anti-roll Bar
  3. Splined Anti-Roll Bar
  4. Hollow Anti-Roll Bars

What is the difference Between a Sway Bar and Shock Absorbers/Struts?

A sway bar connects the opposite side’s wheels in a precise way. It maintains the balance between the wheels. However, the struct bar is connected to the suspension strut tower. It decreases chassis-flex and increases vehicle rigidity.

Can you drive with a bad sway bar?

Yes, you can drive your vehicle with a broken sway bar link, but it can be difficult to steer, including driving on paved roads, taking slow turns, and on freeways that require changing lanes.

What causes the anti-roll bar to go bad?

There are multiple causes that lead the anti-roll bar to go bad such as normal wear and tear, hard driving, heavy impact, or physical damage.

What are the Symptoms of a Bad Sway Bar?

As the sway bar goes bad, it gives one of the below-given signs:

  1. Clunks, knocking, rubbing, or squeaking noises.
  2. You may also feel excessive vibration when you turn the vehicle.
  3. Decreased handling ability
  4. Visibly worn-out bar
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  4. Bad Sway Bar Symptoms and Causes

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