Originally Posted by
o1turbo30v
For the best result, always replace sway bars in pairs! Sway bars work backwards, meaning if you change just the rear bar, you take away grip from the front (and give it to the rear).
The effect of sway bars is actually the opposite. The stiffer the sway bar, the less traction you will have on that end of the car. So, a stiffer sway bar in the rear does not reduce traction in the front, it reduces traction in the rear. I'll go into this in more detail below.
Regarding which sway bars to change, it just depends on how your car handles now, and how you want it to handle after the change. I have had on-line classes from both of these authors and found their materials to be useful. Both authors have many resources available, some are free and some are not. Here are a few free ones to get you going:
How to Tune Your Car's Handling a free pdf file containing 45 pages of information about suspension tuning. It discusses how to modify the handling of a car through suspension modifications, including anti-roll bars:
https://speedsecrets.com/tune-car-handling/
These next two links talk about understeer and oversteer, and the effects of softening or stiffening a suspension. They are written by a suspension engineer from a racing perspective. One of the main points he makes is that when you stiffen the suspension to add traction to the outside tire in a turn, you also lose traction on the inside tire. You can stiffen the suspension to the point that you have less total traction between the two tires. These are worth while if you want to learn more about handling and suspension tuning:
https://www.yourdatadriven.com/under...er-definition/
https://www.yourdatadriven.com/solvi...ndling-puzzle/
Of course there are many ways to modify a suspension, including springs, shocks, strut tower braces, sway bars, alignment, etc., but we are discussing sway bars here so I will focus on that.
First, remember that your car has an independent suspension because that configuration allows the suspension to better adapt to changing road surfaces, keeping the tires in contact with the road surface as much as possible, which maximizes traction. Linking the right and left sides of the suspension makes the suspension more stiff, while also reducing the independent nature of your independent suspension. Less independence equals less traction. For example, a stiffer anti-roll bar in the rear prevents the outside rear suspension from compressing which increases the load on the tire and results in more traction on that tire; however, the same forces that prevent the outside suspension from compressing also prevent the inside wheel from extending, thereby reducing traction on the inside tire. In effect, an anti-roll bar can shift most of the load to the outside tire, leaving you with less overall traction between the two tires. So, it's a balancing act to find the right configuration to maximize traction while also providing balanced handling.
If you don't care a lot about cornering, you can just lower and stiffen everything to change how the car looks and feels. But, if you are concerned with handling, you need to consider the balance of the car in turns. Does it understeer, oversteer, or is it balanced, and what do you feel most comfortable with? From a safety point of view, manufacturers build in slight understeer in most vehicles as it is considered safer and easier to recover from than oversteer. Some cars, like the M2/3/4, build in oversteer to make it more track-focused, but Audis are built with understeer, as are most vehicles.
The first step in good handling is to get tire pressure correct, as the tires are the car's only point of contact with the road and your only source of traction. You need to maximize the size of the tire's contact patch to maximize the traction it can provide, and correct tire pressure is the only way to do that. Too much or too little air pressure will reduce traction in that tire. Once tire pressure is correct you can assess handling and adjust how the car behaves in turns by modifying the suspension.
If the car understeers, that indicates that the front tires have relatively less traction than the rear, so you either need to increase traction in the front, or decrease traction in the rear. Conversely, if the car oversteers, that indicates the front tires have relatively more traction than the rear, so you either need to decrease traction in the front or increase traction in the rear.
Remembering that stiffer suspensions have less traction, and you want to modify handling with sway bars, you would stiffen an anti-roll bar to reduce both body roll and traction on that end of the car, or soften it to get the opposite effect. So, to address understeer you would stiffen the rear and/or soften the front sway bar; to address oversteer you would stiffen the front and/or soften the rear. If you want to change both sway bars, the principles remain the same and the handling you get will be a function of the relative difference between the front and rear sway bars. If the new sway bars are stiffer in the front than rear, you will have less oversteer and/or more understeer. If the new sway bars are stiffer in the rear than front, you will have less understeer and/or more oversteer.
So, if your goal is to reduce understeer, just do the rear; if your goal is to reduce oversteer, just do the front; if you want your handling to be as flat as possible do both, but the ride will be more firm and you will have relatively less traction on all four corners of the car because you are making the suspension less independent.
Finally, if stiff suspensions have less traction, why do track cars have stiffer suspensions? First, the suspension needs to be stiff enough to support the weight of the car and the forces it encounters on the track. Second, as track cars get faster and more aggressive they rely increasingly on aerodynamic down forces to increase traction, and that requires body work to be close to the road surface. If the suspension is too soft, it allows too much suspension movement which would allow the body work to come in contact with the road surface and impact the down force ground effects. Third, the less suspension movement you have, the less impact it will have on steering geometry, thereby making steering response more predictable.
So, track cars will attempt strike a balance between suspension compliance and body work to maximize traction through tires and down force, in an effort to get the best handling for the specific track.
Street cars have to handle well, but they also have to be livable on public roads. In the end, the correct anti-roll/sway bars to change depend on how your car handles now, and how you want it to behave after the modifications. Know what you are trying to accomplish before you start buying hardware.
Front and rear sway bars question
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