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It can sometimes be a challenge to choose the right sway bar for your car and driving style. Replacing the front sway bar will change certain handling characteristics, while replacing the rear will change others. It is not a "one size fits all" situation. Sway bars (anti-roll bars, stabilizer bars, etc.) come in different sizes and shapes, both hollow tube and solid tube. The world of vehicle dynamics and the science of automotive suspension can get very complicated and may seem like a daunting obstacle to tackle. The purpose of this article is to guide you through choosing the correct sway bar for both your car and driving style. This will hopefully simplify the process of upgrading your car's suspension.
Many of you are here solely to learn how a front or rear sway bar will affect the handling of your car. Before getting into how sway bars work, then, I will first provide a brief overview of how a sway bar will affect vehicle dynamics.
Front Wheel Drive (FWD) Cars: A stiffer rear sway bar on a front wheel drive car will reduce understeer. Typically, a front wheel drive car will handle better with a rear sway bar that is stiffer than the OEM piece.
Rear Wheel Drive (RWD) Cars: A stiffer front sway bar on a rear wheel drive car will reduce oversteer. Typically, a rear wheel drive car will handle better with a front sway bar that is stiffer than the OEM piece. Some rear wheel drive cars, however, also understeer. If your vehicle understeers, front or rear wheel drive, a stiffer rear sway bar will make the car handle more neutrally.
All Wheel Drive (AWD) Cars: To put it simply, if you drive an all wheel drive car that understeers, install a stiffer rear sway bar. If you drive an all wheel drive car that oversteers, install a stiffer front sway bar. All wheel drive vehicles all handle a little bit differently, this means that choosing the right combination of sway bars will depend on how your specific vehicle behaves.
How and Why Sway Bars Work
Believe it or not, sway bars are actually very simple suspension components. Sway bars are intended to reduce body roll while a car is turning. When your car turns, the outside of the vehicle will squat while the inside will lift and "unload" due to centripetal forces. This reaction is what is referred to as body roll. We want to reduce the amount of body roll in a performance vehicle because you are taking the weight from the inside tire and applying it to the outside. By doing this, the car is using only one tire to turn instead of two. This reduces the grip of your car and negatively impacts steering. A sway bar reduces body roll by acting as a torsion bar that transfers load (force) from one side of the car to the other. Sway bars connect the left and right suspension components on a car so that when weight is transferred laterally, both the left and right suspension pieces will compress. This distributes the turning forces more evenly across both sides of the vehicle and helps it stay flat through the turn.
Because front wheel drive, rear wheel drive, and all wheel drive vehicles behave differently, they all respond differently to sway bar upgrades. A front wheel drive car relies on the front tires to both turn and transmit power to the ground. Because of this dual use of the front tires, front wheel drive cars tend to understeer. By increasing the stiffness of the rear sway bar on a front wheel drive car the rear inside wheel of the car will want to lift, and as such you can reduce body roll. This will help keep the car pointed generally in the right direction. You may want to be careful with upgrading the front sway bar on front wheel drive cars because too much stiffness in the front can cause the inside front wheel to lift. Because the front tires are putting power to the ground, this would drastically affect the cars grip and handling in a negative way.
Rear wheel drive cars allow the rear of the car to pivot around the front, and as such they tend to oversteer. By increasing the stiffness of a rear wheel drive car's front sway bar you can help to decrease oversteer in a corner. Since, in this case, the rear wheels are driving the car, we want to keep them planted. To reduce body roll, however, the front sway bar can be stiffened without negatively affecting suspension dynamics.
All wheel drive cars are a combination of both front and rear wheel drive layouts. Naturally then, all wheel drive cars can either understeer or oversteer from the factory. This means that such vehicles can greatly benefit from both aftermarket rear AND front sway bars. However, the front wheels are still transmitting power to the ground. Because of this, it's important to make sure that you don't go too stiff in the front or risk inducing more understeer.
How to Install a Sway Bar
Notes to Keep in Mind
A larger sway bar is not necessarily stiffer. Aftermarket sway bars are typically sold as either solid or hollow tubes. Since the elasticity of a sway bar is a result of cross sectional area (stiffness = [area*young's modulus]/length), the overall diameter doesn't matter so much. For the most part, solid tube sway bars are stiffer than "larger" sway bars made of hollow tube. This is because the hollow metal tubing actually has less cross sectional area and therefore has less resistance to bending moments.
Stiffer sway bars are not always better. While increasing the stiffness of the rear sway bar in a front wheel drive car might reduce understeer, an overly stiff rear sway bar can actually induce oversteer and make the car difficult to drive. Likewise, a rear wheel drive car with an overly stiff front sway bar may tend to understeer. When it comes to suspension, the name of the game is balance.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Tolga on April 11, 2020:
“By increasing the stiffness of the rear sway bar on a front wheel drive car the rear inside wheel of the car will want to lift, and as such you can reduce body roll.” Phrase is not correct I guess rear inside wheel want to snip on to the ground
Ryan on March 04, 2019:
Chris's comment pretty much nailed it and saved me from writing out my own essay
Mobius on July 15, 2017:
Never take structural advice from a gearhead...
Chris on June 11, 2017:
Hi, I believe your description of stiffness of solid vs hollow ARB's in very incorrect. You stated a couple things which are not true. The first and most important on is that you said the stiffness in bending is what is important. This is incorrect. ARB's are loaded primarily in torsion. The torsional stiffness is dependent on the polar moment of inertia. For a circular bar of radius R its polar moment would be (pi*R^4)/2 If that same bar instead was hollow and had an outer radius of R and an inner radius of r, its polar moment of inertia would be Pi*(R^4-r^4)/4. If you run the numbers you will find that for an equivalent weight, you can achieve far higher stiffness from a hollow tube than a solid one. In fact, this is true for both torsion and bending! Additionally, your statement that stiffness=E*A/L is only correct for axially loaded members (tension or compression only) ARB's are neither! Hopefully this helps someone with the desire to understand what is truly at play here.