Sway bars are given many names, from anti-roll bars to stabilizer bars, and it can be confusing if you don’t know what any of these terms mean. There are many ways you can improve your car’s handling, and sway bars are one way to do it.
A sway bar helps stabilize a vehicle and stops it from swaying one way or the other. It only has an impact when a vehicle is turning and the vehicle starts to lean, usually outward. The sway bar twists when the vehicle sways, providing tension to the suspension and stabilizing the vehicle.
The particulars of how sway bars work are fascinating and a testimony to the advanced technology that goes into our vehicles today. The following is a brief summary of the sway bar and how it does what it does.
What Is A Sway Bar?
A sway bar helps stabilize your vehicle as you take a corner. It is needed because every vehicle leans (or sways) outward when the vehicle turns. The faster the driver takes the corner, the more the sway bar works to stabilize the vehicle, as the more the car wants to ‘roll.’
The sway bar keeps the vehicle from rolling, which is why they’re often called anti-roll bars. The force of the vehicle pushing outward when turning is great enough to cause the vehicle to want to roll to one side. The faster the turn, the greater the vehicle sway, which means the greater the chance the vehicle will roll.
Take that one step further. Imagine if NASCAR vehicles did not have sway bars. NASCAR cars tend to go around corners much faster than the average driver. Imagine what would happen on courses with big turns, like Daytona, flatter turns, like New Hampshire, or multiple different kinds of turns, like at Watkins Glen.
In every case, the outward force on the racecar causes sway, and if the speed were high enough, there would be a risk of the vehicles rolling over. If a vehicle did not roll over, the driver would be fighting the outward force and be moved around whenever they made a turn. On road courses, that would get exhausting very quickly.
How Do Sway Bars Work?
When you turn your vehicle, a few things happen. First, your vehicle is pushed by momentum outward from the point that you start to turn. The weight of the vehicle shifts from one side to the other and the weight transfers to the outside tires. In turn, this reduces the grip you have on your vehicle’s inside front tire, which affects the traction you have.
Without a sway bar, that momentum shift would only build as the vehicle turned. Couple that with disproportionate weight on the front and you have a recipe for two things:
- A very hard to control vehicle
- A vehicle that is prone to roll to the outward tires and flip if the momentum is high enough
The sway bar uses torsion to compensate for the weight shift and negate the outward momentum.
How Sway Bars Stabilize
The metal sway bar is a torsion spring. One end is attached to the left wheel and the other to the right, front or rear, so that when a single wheel raises, the bar twists. The sway bar fights the twist and restores the wheel to its natural height, which levels the vehicle. When a vehicle has no outward force on one tire or the other, the sway bar is inert.
That stabilizing effect helps a driver maintain control and also counters the tendency of the vehicle to roll outward and potentially flip. It is particularly important in cars with higher centers of gravity as those vehicles tend to roll easier. Without the sway bar, a racecar would become almost impossible to manage when going through turns.
However, aside from preventing the car from flipping over, sway or anti-roll bars are also designed to improve the car’s handling. By limiting the weight transfer and creating more even weight distribution across all four tires, you experience higher levels of grip and therefore better handling.
Different Types Of Sway Bar
1. Solid Or Hollow
A solid sway bar tends to be tighter, to produce more torsion. That means it is more difficult for a vehicle to start to sway when turning. This is because the greater the torsion, the greater the resistance, which creates an equal but opposite effect on the opposite wheel.
A solid sway bar tends to right a lot tighter and not have any give or take (or very little). This controls any weight or momentum shift. It essentially holds the vehicle steady as it goes through a corner.
The hollow sway bar has a lot more give. It has less metal to twist, so it twists easier, and its torsion is less. That also means it twists quicker and more than a solid sway bar. With a hollow sway bar, momentum will shift more and correct slower.
2. Diameter And Length
The stiffer a sway bar is, the less the wheels can move. That decreases the transfer of weight from one side to the other. A stiffer sway bar creates more resistance to a roll. The larger a sway bar is the heavier it is and the less roll the vehicle will experience.
A 1-inch thick sway bar that is 38 inches long would weigh a little over 8 lbs. A sway bar 1.5-inches thick and 38 inches long would way a little over 18.5 lbs. The amount of twist allowed in the heavier bar would be more than the amount of twist the smaller bar would tolerate. The lighter the bar, the less resistance to weight transfer and the greater the roll.
With a hollow sway bar, the same principle applies. The difference is that a hollow sway bar will start out allowing more twist than a solid bar. That means from the outset, the weight transfer would be more with a hollow, lighter sway bar and the allowed roll would be greater.
3. Impact of Weight
The thicker the sway bar, the more resistance and less roll, but it will also be heavier. Heavier sway bars add weight to the end at which you add them. That can make a vehicle “looser” going into corners.
Tight And Loose
You hear these terms a lot in racing. Along with the momentum of a weight shift and direction change, a vehicle’s alignment also has tendencies when cornering. A vehicle’s alignment can be balanced, loose, or tight.
Loose is when the back end of the vehicle wants to come around the front of the vehicle in the direction of the turn. Tight is the opposite: A vehicle’s front end wants to spin backward and overtake the rear of the vehicle.
A Delicate Balance
What that means is that, as you are reducing the amount of sway in a vehicle (with sway bars at the front), you are increasing the vehicle’s front-end weight, which causes the rear to want to encircle the front. That has to be accounted for in addition to the needed sway control.
Are Sway Bars Worth It?
A sway bar is worth it as, in everyday driving, the more control you have over your vehicle, the better off everyone is. A sway bar that corrects sway helps you maintain control. While better handling is obviously a good thing for any driver, the decreased likelihood of rolling the car is also good.
In racing, the combination of sway and roll creates a situation where maintaining control of the racecar becomes very difficult. In the worst-case scenario, the driver cannot control it and causes a wreck. But even outside of the worst case, drivers in any racecar always need to have as much control over their car as possible in order to go as fast as possible.
Does Your Car Need Sway Bars?
Not every vehicle needs a sway bar. Most, however, do. To determine if yours does, check your operator’s manual or contact the manufacturer. When your vehicle needs a sway bar but lacks one or if you have a broken one, it can be more susceptible to swaying or even rolling in corners at high speed.
Swerving
With nothing to control the momentum and weight shift, your vehicle would sway repeatedly, and occasionally it would sway enough to move your trajectory. When that happens, you would have to correct, which could cause a swerve. Clearly this could be dangerous, but it won’t be as dangerous at low speeds.
Loose Steering Wheel
Another issue would be that your steering wheel could turn very loosely. Depending on where the car is loose, you may be more susceptible to oversteer or understeer. This can be very dangerous at high speeds, and it’s very undesirable if you use your car on the track.
Increased Wear And Tear
The more you fight your vehicle, the more it is prone to wear down or break. Constantly fighting it on every corner is a recipe for several components to wear faster, including your tires, brakes, and multiple steering components. Given that sway bars can offer better control of your car, they can therefore help minimize this wear and tear.
Sway Bars vs Shock Absorbers
Shock absorbers do a lot of things but the important thing they do is cushion the wheel when it goes over a bump. A sway bar corrects the balance of the vehicle when one wheel raises or lowers. Both are important, but their two roles are quite different.
While shock absorbers are designed to prevent excessive bouncing and provide you with a more comfortable ride, they do little to offer more control of the car in the corners. Sway bars do this, but they don’t provide any additional comfort or stability when going over bumpy terrain.
Sway Bars vs Torsion Bars
While both are important to a vehicle in the right context, sway bars and torsion bars are very different. They perform different roles and produce different outcomes.
A torsion bar helps support a vehicle. When you run over a bump, if your suspension has a torsion bar, the torsion bar helps level the vehicle. It returns the vehicle from the bump alignment to the vehicle’s regular alignment. This keeps everything in the vehicle even and steady, preventing things like load shift, and functioning in a similar way to the shock absorber.
A sway bar fights weight transfer and subsequent swaying. It helps stabilize the trajectory of the vehicle and reduces sway momentum. This helps keep it steady and helps the driver maintain control when turning a corner, but again it does little in the way of keeping it level like other aspects of the suspension when driving on uneven terrain.
Final Thoughts
Sway bars are bars that connect the right side of your suspension to the left side, and they minimize the amount of roll your car has in the corners, offering better traction and control. A sway bar helps your vehicle take corners without rolling, particularly if you take a corner at high speed.
I created and have been writing on this site since 2019, collaborating with drivers, coaches, engineers and manufacturers to provide you with the most reliable information about motorsport. Find out more about me here.