Do sway bars really work?

lopperman

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I installed a Progress Sway Bar on my ‘17 Civic Sport Hatch yesterday. It was an eye opening experience when I installed it to see how the end links worked. The end links have quite a bit of horizontal give, and it made me wonder how adding a stiffer sway bar makes any difference, since it’s connected by the end links, and the end links move around. Can anyone shed some light on this? And if it only deals with vertical movement, then what’s the point of getting a stiffer bar? Does the stock bar actually flex vertically?

And FWIW, my back end doesn’t seem much stiffer than it was with the stock sway bar.





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Lovic87

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They help with body roll and flatter cornering, which in turn assists with weight transfer and helping the rear end rotate. The "give" from the end links needs to be there unless you drive on glass smooth roads 100% of the time, as the suspension needs to be able to articulate.

Upgrading the rsb on my TL to the Type-S piece made a nice difference, but regular, day to day driving is exactly the same. Hard cornering is when you really notice the difference between rear sway bars.
 

totopo

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anti sway bars limits the difference in deflection (up and down position) between two tires. so when one goes up it acts as a spring pulling the other tire up. they arent that easy to twist by hand so it's not super apparent, but yes, they act in the vertical direction and they act by twisting (why they are also called torsion bars). so when one arm gets pulled up it tries to pull the arm on the other side up. this limits body roll which is nice for autocross and transitions but even though flat body roll is associated with sports cars, the lack of body roll is a secondary effect and body roll in and of itself is mostly just driver preference on a road track.

the main aspect in respect to vehicle dynamics is the weight transfer on that axle. Weight transfer is mathematically determined by cog and wheelbase and the TOTAL weight transfer is unavoidable. Weight transfer is bad for performance. When you stiffen anti-sway bars on an axle, say the rear as is popular here, you increase weight transfer on that axle, which causes less traction during cornering, but it does so by decreasing weight transfer on the front axle, increasing cornering performance on that axle. So stiffer anti-roll bars in the rear causes increased oversteer.

For example, say in a given cornering speed and condition and yadda-yadda-yadda you have 1000lbs of lateral weight transfer. Say you have a perfectly neutral balanced car at steady state, you will have 500lbs of transfer on the front, and 500lbs of transfer on the rear. Say you increase the rear anti-roll bar and now you have 750lbs of transfer on the rear, lessening cornering performance, you now only have 250lbs of transfer on the front, helping out the front.

People seem to like oversteer balance because its kinda fun to toss the car around at low speeds and have the rear slide a little, but it's not like the civic x is that understeer balanced on the whole... I would want to be comfortable in dealing with over-rotation in the car before making it more overstter happy. I kind of feel like this generation civic is pretty decently balanced for most drivers. Alot of good autoX-er's, who in general like a little overrotation, are reporting that stock balance isn't too bad.

If you overspeed into say a 70mph corner and enter at say 75-80mph, then you are kind of hosed if you are in an oversteer happy fwd car. If you had a base civic, you might be okay with just turning the wheel and praying as most drivers will do and you will probably scrub off enough speed to not crash since it may have enough understeer tuned in to avoid lift-off oversteer. If you have neutral or oversteer tuned car, then if you lift off the gas you will spin out and crash from lift off oversteer, if you brake you will spin out and crash because the rear to front weight shift will make it even more tail happy. you have to gently apply gas and turn and pray for the best but because you are going to fast you will probably not scrub off enough speed and will hit the outside wall, then spin, then crash.
 

marauderguy

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The Progress bar made a considerable difference on my car. I like to push off ramps to the limit and it's absolutely crazy how this thing sticks. I have never encountered even a hint of oversteer.
If your only driving to 80% of the limit, then its probably not a worthwhile upgrade.
 

totopo

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i beg to disagree. If you think that freeway on/off ramps are taking your car to 100%... You really should go to a road course.

I find that hard to believe because in my wife's stock civic hatch, I can and have induced oversteer, which is pretty consistent with what the auto-X'ers have reported.

Ugh, it's the Dunning-Kruger effect. How do you know that those giving advice are worth taking advice from.
 
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lopperman

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The Progress bar made a considerable difference on my car. I like to push off ramps to the limit and it's absolutely crazy how this thing sticks. I have never encountered even a hint of oversteer.
If your only driving to 80% of the limit, then its probably not a worthwhile upgrade.
I also have a front strut bar. I wonder if my front is too tight. I’ve read that you want to have the front looser than the back.
 

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Noticeable difference on my Sport HB with the Progress, first I've heard anyone say they felt no difference, all have said night and day difference.
 
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lopperman

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Noticeable difference on my Sport HB with the Progress, first I've heard anyone say they felt no difference, all have said night and day difference.
One thing I did realize, I had the stabilization control turned on when I took it out and drove it hard. Would that make a difference? Should I try it with that turned off? I think the stabilization control will automatically apply inside rear brake.
 

totopo

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I also have a front strut bar. I wonder if my front is too tight. I’ve read that you want to have the front looser than the back.
If you increase both the front and rear anti-roll bars by the same percentage then you won't be changing the balance of the car. You will just make it have less body roll. A lot of people like how that feels, it gives people confidence, though it limits feedback to the driver. It is good for auto cross, because the suspension takes less time settling in transitions, but it doesn't really have any effect on a road course; it is mostly driver preference. It is like the difference between a ft86, which goes for flat feel for fun vs the miata, who goes for more roll for better driver feedback.

If you want to increase oversteer, you want your front anti-roll bar lighter and your rear stiffer.

One thing I did realize, I had the stabilization control turned on when I took it out and drove it hard. Would that make a difference? Should I try it with that turned off? I think the stabilization control will automatically apply inside rear brake.
The stabilization will help in everything. If you overspeed and are pushing, it kills your speed and helps you rotate. If you over-rotate, it tries to bring the car back straight. If you are purposefully trying to upset your car, then yes, the traction control will prevent it and differently depending on if you are under or over rotating.
 

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In normal driving I just noticed the car goes easier in tight corners, like right hand turns. Like the car just wants to go round with ease.
Just try taking a familiar right hand turn a few ticks faster by braking a little less.
On the track, not sure it helps with having a more planted rear.
 

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