Sway Bars & Anti-Roll Bars | How They Work and Which One You Need
Picture this, you take a sharp turn in your car and feel your beloved hot rod rolling to the side. That body roll reduces tire grip and makes the car feel less stable.
What is a Sway Bar & What Does a Sway Bar Do?
Sway bars (also known as an anti-sway bar or anti-roll bar) are a suspension component designed to combat that very problem. It’s essentially a steel bar linking the left and right wheels on an axle. By connecting both sides, the sway bar acts like a torsion spring that limits roll by forcing the car to settle down rather than roll to one side or another.
When the car corners and centrifugal force pushes the vehicle to the outside, rolling that side of the suspension down, the sway bar twists and pulls the inside suspension down too so the chassis stays more level. In other words, it transfers some of the load to the lighter inside wheel, helping distribute weight more evenly across all tires. The result is reduced body lean and improved stability during cornering. Importantly, a sway bar only really comes into play when one side of the suspension is compressed more than the other (such as in turns or uneven bumps). It adds roll stiffness in corners without significantly affecting the ride over flat, even bumps. This means you get flatter handling through curves without a major ride comfort penalty in normal conditions.
Anti Roll Bar Vs Sway Bar
If you’ve heard terms like “anti-roll bar,” “anti-sway bar,” or “stabilizer bar,” don’t be confused – they all refer to the exact same part. “Sway bar” is simply the popular shorthand. The term anti-roll bar is common in engineering contexts (and in Europe) because the device’s job is to resist or counteract body roll. In everyday garage lingo, sway bar or anti-sway bar is used because it controls the car’s swaying motion in turns. Functionally, there is no difference, both are solid or tubular spring-steel bars connecting opposite wheels to limit body lean. One minor nuance is in drag racing circles a heavy-duty rear anti-roll bar is used to control torque twist on launches, but it still operates on the same principle as a sway bar. Bottom line, whether you call it a sway bar or anti-roll bar, it’s the same device helping your car corner flatter and handle more predictably.
Are Sway Bars Necessary?
Nearly all modern cars and trucks are equipped with sway bars from the factory because they are critical for predictable, stable handling in everyday driving. Especially on taller vehicles like SUVs or off-road Jeeps with a high center of gravity, sway bars are necessary to reduce excessive body lean and the risk of rollover. Typically, without a sway bar the vehicle will feel looser and less predictable in quick maneuvers or at the limit of tire grip. In fact, if your car was originally equipped with one, removing it will make cornering feel sloppy and can be dangerous at speed. During normal street driving, a sway bar provides added stability and a more connected, confidence-inspiring feel to the road.
However, there are a few scenarios where you may not want a sway bar. For example, in drag racing some drivers disconnect or remove the front sway bar so the front suspension can rise and transfer weight to the rear wheels for better traction off the line. In this case, eliminating the front bar can help shift weight rearward during a hard launch. However, even drag racers will add a stout rear sway bar because it keeps the car tracking straight by planting both rear tires evenly. Another scenario is serious off-road rock crawling, where sway bars are usually disconnected to maximize wheel articulation.
Do Rear Sway Bars Make a Difference
Installing or upgrading a sway bar can make a noticeable difference in how your car handles. By reducing body roll, a stiffer sway bar keeps the car steady through the turns and actually lowers ride height, maximizing the contact patch on all four tires and available grip. Even in everyday street driving, a car with well-tuned sway bars will feel more stable in lane changes and cornering, giving the driver more confidence. If you’ve ever driven a classic car or truck without sway bars and then added them, the improvement in cornering flatness is dramatic. Modern performance cars rely on beefy sway bars to achieve that “rail-like” cornering feel. While cornering hard a sway bar helps share the load between the outside and inside tires, so the car stays flatter and handles better.
Upgrading from a small factory bar to a thicker aftermarket bar (or adding a rear sway bar to a car that only has a front bar) can sharpen handling significantly. However, there is a balance to strike. A sway bar that’s too stiff can have downsides, like a rougher ride on uneven roads or causing the car to push (understeer) or skate over bumps. If you hit a pothole with one wheel, an overly stiff bar will transmit more of that jolt to the opposite wheel, which can make the ride feel harsh and “nervous” on rough pavement. Manufacturers take this into account when tuning suspensions, and some high-end vehicles even use active sway bars that soften or stiffen on the fly to balance comfort and handling. But for most of us, a carefully chosen sway bar upgrade yields a positive change in handling performance with only minimal impact on ride quality.
Sway Bar Components & Sway Bar Diagrams
A sway bar is more than just a bent metal bar; it’s a small system of parts that must work in harmony. The main component is the bar itself, a spring-steel rod (often U-shaped or curved to fit around other suspension bits) that spans the width of the vehicle. It can be either a hollow tube or a solid round bar. There are some exceptions, but normally the middle of the bar is attached to the chassis or subframe at two points using bushings nested inside of steel brackets that clamp to the frame. This is so the bar can pivot.
These bushings are usually rubber or polyurethane. Sway bar rubber bushings flex easily to absorb noise and vibration, but they can also deform. Polyurethane bushings are stiffer for sharper response but can transmit more noise. Over time, bushings wear out and may need replacement. In fact, if you ever hear clunking over bumps, worn sway bar bushings or bad end links are often the culprit.
What Do Sway Bar Links Do
At each end of the sway bar, you’ll find the end links. Sway bar end links are rods with ball-joints at the ends that connect the very ends of the bar to a moving part of the suspension—either the lower control arms in an independent suspension or the axle housing in a straight-axle setup. End links can be simple straight links with bushings or more elaborate ball-jointed links that allow movement. When one wheel goes up or down, the end link transfers that motion into the sway bar by twisting it. Many aftermarket end links are adjustable in length, which is useful for eliminating any preload on the bar, especially if a car is lowered, and some use heavy-duty ball joints or heim joints for maximum precision.
The bar, bushings, and sway bar end links make up the basic system. Some performance sway bars are one-piece designs with forged or bent ends, while high-end racing bars have splined ends with separate lever arms. In a splined setup, the center bar is a straight spring steel rod with splines on the ends, and you attach aluminum arms to those splines. This allows easy tuning by swapping the bars with different thicknesses for tuning. The sway bar itself can be either solid or tubular. Solid bars are heavy but strong, compact, and less expensive, often used in OEM applications. Hollow sway bars save weight while maintaining similar torsional stiffness, which is great for performance cars where every pound counts. But they can also be thicker, making it more difficult to fit a hollow bar inside the tight confines of a street car.
Choosing the Right Sway Bar
Choosing the ideal sway bar setup depends on your vehicle and how you use it. A track racer’s needs differ from an off-roader’s, which differ from somebody with a daily-driven street car. Here are some key factors to consider:
Driving style and goals: If you prioritize comfort and daily drivability, you might lean toward a moderate or smaller bar. If spirited cornering and performance are your goal, a larger, stiffer bar can provide the flat handling you’re after at the expense of some roughness. Generally, thicker bars are better for performance and sharper handling, while thinner bars that flex more will offer a softer, more compliant ride for everyday use.
Vehicle type and suspension design: Every vehicle is different. A sports coupe with a low center of gravity might handle great with a very stiff bar, but a tall 4x4 SUV might become skittish with the same stiffness. Consider your vehicle’s suspension layout, weight distribution, and any existing handling tendencies. For example, a rear-heavy sports car that already oversteers may not want a much thicker rear bar (as it could oversteer more). It’s often wise to consult the manufacturer’s recommendations for your specific car model to see what’s worked for others. Also, ensure any bar upgrade is compatible with your other suspension mods (like springs or coilovers) for a balanced setup.
Handling balance: You don’t always have to upgrade both sway bars. Changing the front or rear bar independently is a common way to fine-tune your handling balance. Increasing front sway bar stiffness tends to reduce body roll up front, but if done in isolation it can induce more understeer, and the car will push wide through hard turns. Increasing the rear bar’s stiffness will tighten up the rear end and can reduce understeer, making the handling more neutral or even oversteer if pushed.
So, think about your car’s behavior. If it’s front-heavy and plowing (understeering), a bigger rear bar, or a moderately stiffer rear bar relative to the front can help the car rotate better in corners. If the car is tail-happy (oversteering), a thicker front bar or softer rear bar will help stabilize it. The goal is a neutral balance where front and rear work in harmony. Many aftermarket sway bar kits are sold in matched front-rear pairs for this reason. However, you can mix and match to dial in the feel. For instance, some autocrossers run the biggest front bar possible on a front-wheel-drive car to keep it flat, while leaving the rear softer to maintain traction.
Adjustability: If you like to tinker or your vehicle sees a variety of uses (track days on weekends and commuting in the week), an adjustable sway bar might be worth it. These bars have multiple end link sway bar mount positions or other mechanisms to alter leverage on the bar. By choosing an inner hole vs outer hole, you effectively shorten or lengthen the lever arm, which changes the bar’s stiffness. This allows you to fine-tune handling without swapping parts. You could start on a softer setting for daily driving, then go stiffer for a track day. Adjustable sway bars provide a great deal of flexibility in dialing in your preferred handling balance. Just remember to adjust both sides evenly and re-check your end link lengths when changing settings.
Beyond these general factors, consider any special use cases for your vehicle. For instance, off-road driving has vastly different demands. If you frequently take your 4x4 on rock-crawling trails, a super stiff sway bar will actually hinder you. In off-road situations where wheels need to move freely to maintain steady contact with uneven terrain, an overly thick sway bar will limit suspension articulation. You may end up with one wheel in the air since the bar is trying to keep the axle flat. That’s why many off-roaders install quick-disconnect sway bar end links or sway bar disconnect kits. These let you unlink or slacken the bar when hitting the trails, so each wheel can move independently for maximum traction.
On the flip side, if you’re building a drag racing car that will mostly see straight-line duty, you might prioritize a strong rear anti-roll bar and possibly delete the front bar to optimize weight transfer, as we discussed earlier.
Is a Thicker or Thinner Sway Bar Better?
This question boils down to what handling characteristics you desire and the trade-offs you’re willing to accept. A thicker sway bar twists less easily, while the increased propensity to twist in a thinner bar dampens some of the movements that get transmitted from one side of the car to the other. Go with a thicker bar when you want to reduce body roll and sharpen handling as much as possible. For example, if your car feels too sloppy in corners, leaning over on the outside tires, a thicker bar will tighten it up and make it feel “flatter” and more planted. You’ll typically gain quicker transient response (the car settles faster in left-right transitions) and overall stability with a bigger bar. This is why performance-oriented drivers and racers often opt for the thickest bar that still maintains a good handling balance. As noted, adding a thicker rear bar is a common trick to combat understeer in front-heavy cars. It increases roll stiffness at the rear, which can help the car rotate through a turn. Likewise, a thicker front bar can help calm down a tail-happy oversteering car by adding roll stiffness to the front, making the front end push a bit more instead of the rear stepping out.
On the other hand, there are times when a thinner sway bar is the smarter choice. A thinner bar is relatively soft in twist, allowing more independent wheel movement. This can be beneficial for ride comfort and rough terrain. If you frequently drive on potholed streets or value a smooth ride, a thinner bar will let each wheel navigate bumps with less impact on the opposite wheel, resulting in a more compliant ride. Also, in scenarios like rally racing or bad-weather driving, too stiff a bar can cause the inside tire to unload too much over uneven surfaces, reducing grip. A bit more body roll can actually help keep all tires in contact with the ground on uneven roads. For off-road crawling, you actually want a very thin bar or none at all to allow maximum wheel articulation. So, choose a thinner bar if you find your vehicle’s suspension needs more independence between left and right, or if the car feels skittish over bumps with a big bar.
It’s all about balance. Manufacturers tune sway bar thickness to the vehicle’s weight and suspension. If you modify the car (lowering springs, different shocks, added weight, etc.), re-evaluating sway bar thickness is wise. A good rule of thumb is to use the thickest bar that still gives you good tire contact and the handling balance you want. If you go too thick at the front, you might notice the car starts understeering at the limit. Too big in the rear and it will start oversteering. Many enthusiasts experiment with different diameters to dial in what feels best.
Are Aftermarket Sway Bars Worth It?
For most enthusiasts and even casual drivers looking to improve their vehicle’s handling, aftermarket sway bars are absolutely worth it. Upgrading your sway bars is one of the simplest and most cost-effective ways to dramatically enhance cornering performance without a full suspension overhaul. A quality aftermarket sway bar, especially when paired with good shocks and tires, can make your car feel like a whole new machine in the curves.
On a performance car or race car, a stiffer bar can shave seconds off lap times by keeping the chassis flatter through turns. Even on a daily driver, you’ll notice the car stays more composed during sudden swerves or highway on-ramps, which can enhance safety. A sway bar upgrade makes the car feel more planted and confident, especially in emergency situations.
From a value perspective, aftermarket sway bars give a lot of bang for your buck. They typically aren’t very expensive, and most bolt to factory mounting points and can be installed with basic hand tools in an afternoon. When shopping, it’s wise to stick to reputable brands and match the bar to your use-case. In terms of specific products, companies like Speedway Motors have been supplying performance sway bars kits for decades. Speedway, for example, offers a wide variety of direct-fit sway bar upgrade kits for classic muscle cars, trucks, and racing applications, as well as universal kits for custom projects. You can find everything from high-tech splined sway bars that give you an edge on the track to tried-and-true solid bars for street cars. The support and knowledge from established vendors can be invaluable in choosing the right bar for your vehicle.
Ultimately, if you’re looking to improve handling, an aftermarket sway bar (or a matched set of front and rear bars) is a worthwhile upgrade. Just be sure to choose the appropriate size and type for your goals. When correctly selected, aftermarket sway bars offer a significant performance gain with very few downsides. As a bonus, you’ll likely enjoy driving your car even more thanks to the sportier handling. So, strap in, flatten those corners, and enjoy the difference!
