If you have a car that was built after the mid 90’s, more than likely it came from the factory equipped with front and rear sway-bars. A sway bar is a “C” shaped torsion spring that connects the left and right suspension arms of the car together. Generally speaking, as long as both wheels that the sway-bar is connected to are sitting at the same height, the sway-bar is only applying minimal force if any. But when one side is compressed or extended more than the other, that is where the sway-bar starts to do its work because the bar is being twisted.


The reason that sway-bars are put on a car is to reduce body roll. When a car goes into a corner, the weight transfer will compress the suspension on one side, and extend it on the other, and connecting a sway-bar to both sides of the suspension means that the more that a sway-bar resists that movement, the less the car’s body will roll over. If the car’s body rolls less, it feels like the car has more grip and is more stable in the corner.


I will mention at this point that around the world, sway-bars are also called roll-bars and anti-roll bars. They are all different names for the same thing, and the all describe the job that the bar does in a different way.


What makes sway-bars a powerful tool to tune your suspension and the handling characteristics of your car is the fact that there is a separate sway-bar on the front and rear suspension. Staggering the thickness of the bars, and adjusting the point on the bar where the end-link is connects the sway-bar to the suspension both adjust the spring rate of the bar, and therefor how much the bar will resist roll at that axle. Because sway-bars are usually easy to install, and easy to adjust, this gives you a lot of control over how the car handles.


Generally speaking again, if you have a larger/stiffer front sway bar than the rear, the car will tend more to understeer. If you have a larger/stiffer rear sway bar than the front, the car will tend more to oversteer. And if the sway-bars that you chose are adjustable at both ends, then you have a quick ability to tune the handling of your car.


And there is one other function of sway-bars that is worth mentioning. Because they are not being called into action until when both wheels are equally loaded, they have a very minimal effect on ride quality. So at somewhat of an extreme, you could have a car that is softly sprung to give you better ride quality, but a stiffer sway-bar so that you still have minimal body-roll in corners. Or to put it another way, you can put on stiffer sway-bars to make your car flatter in the corners with a minimal impact on ride quality.


Related to this, it is worth mentioning that if you do put on coilover suspension, or put on springs that have a higher spring rate, your need for a stiff roll bar will go down. As the spring rate goes up, the spring itself resists body roll more and more, so you need the sway-bar to intervene less.


Keep in mind too that because the sway-bar connects both sides of your suspension together, the stiffer that bar is, the less you are letting each side move independently. So for a Rally car for example, you are driving on rough roads so you need your suspension to be able to adsorb odd bumps and dips to keep the car moving smoothly so a stiff sway-bar would not be ideal for that application.


Since if you are reading this you most likely have a WRX or STI, I did want to take a moment to talk about good starting points for picking sway-bars for your car.


First, if you have a GD WRX or GD STI which would be from 2002 – 2007, you have Macpherson suspension front and back, and a good starting point is with a “square” set of bars. That means the same thickness at both ends. We really like Whiteline Sway-Bars because the offer a variety of sizes for these cars that also offer a good range of adjustment. The Whiteline 22mm front and rear bars have proven to be a great set for either a WRX or STI here, and they will let you set the car up to be very neutral, etc.


If you have a GR/GV WRX or STI, then you have Macpherson suspension in front, but multi-link suspension in the rear. What we have found here is that these cars rear suspension does work more effectively than the previous chassis, and that makes the car tend more naturally to understeer because the rear tires have more grip. So a good starting point here is actually a staggered sway-bar set-up with a slightly larger bar up front. In fact, Subaru started putting a larger bar in front with some of the WRX’s and STI’s getting a 21mm front.

So for the GR/GV, a good starting point is a 22mm front and 20mm rear bar, or a 24mm front and 22mm rear bar. That should let you set the car up to be neutral, etc. And if you simply want to tune out the understeer tendencies of the car, you could also try just putting on a 20mm rear bar with the stock front.


Hopefully that gives you a starting point, and as always if you have any questions at all, please don’t hesitate to reach out to us.


Thanks for reading and Stay Tuned!

- Jon Cooley