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Bruce Allert's Avatar
 
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Question Sway Bar - How it works???

I just installed a stock front sway bar. Would someone please explain (in terms that I can understand) how it works, what it does and what is loading?
Before I had the sway my cars rear would swing around on wide or sharp corners. Now it just seams to drift sideways. I don't know if this is understeer or??? I'm about to put the rear sway on & see what happens. Maybe I had the rear tires too high in pressure??? Obviously I don't know what I'm doing but it is fun.
bruce

P.s. The tires I'm running are Nito 205/50/15. 35 psi all around.
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Old 09-23-2003, 08:47 AM
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In simple terms, an Anti-Sway Bar will reduce body roll since it attached to each side of the car and is allowed to twist in the middle. Since it is steel it trys not to twist so the force that is fighting the twist will result in the car staying flatter when cornering hard. Of course this will immediately affect all other areas of the suspension such as shocks, springs, track and even tire selection. That is why those big $$$$ race teams have trailers full of springs, shocks and sway bars so they can adjust for different track conditions. A final thought, I'd recommend lowering tire pressure to about 28# front/rear to get better grip as 35# is too high and you'll slide more. Good luck
Old 09-23-2003, 09:05 AM
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Basically it's using a torsion bar to leverage one side of the suspension against the other side. This is a force that only counteracts differences between the two sides, yet lets both side move together without any effect. Does that make any sense?
Old 09-23-2003, 09:07 AM
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Oversteer is where the tail of the car swings out. Can be fun, but is about a heartbeat away from being a spin. Understeer is where you turn the wheel and the car goes straight--or at least, straighter than you are pointing the wheel. Usually considered "safe", because you can back off the throttle (something of a natural first reaction) and reduce the understeer.

"Loading" is simply the amount of weight on a given tire, or the amount of force pressing it down. (Note I said "weight", which is a force, not "mass". You don't get significant changes of mass when the car moves, you do get significant changes of weight as the car goes around corners and so on!)

When you go into a corner, the car will lean toward the outside. Why? The wheels of the car are at ground level, but the car's center of mass is above ground. Centrifugal force (actually the centrifugal component of inertia, but close enough for this exercise) acts at the center of mass, pushing on the middle of the car. The wheels are (trying to) stick to the ground, which means the car will lean toward the outside of the turn.

When this happens, the outside springs (toward the outside of the corner) are compressed and the inside springs lengthen. Load is transferred from the inside wheels to the outside wheels. The body of the car leans, and since the tires and wheels and such are fastened to the body (particularly with a strut-based suspension such as ours), the tires lean as well. This reduces the tire's contact patch (amount of tire in contact with the pavement) and reduces overall grip. In addition, a tire that is more heavily-loaded will grip more, and one that is more lightly-loaded will grip less. But the amount lost on the lighter one is more than the amount of traction gained by the heavier-loaded one.

So we want to keep the body of the car more level, even though we have a force that is trying to roll the car.

What we do is tie the wheels on one end of the car together with something spring-like. Now, when the car leans, the outside spring is compressed, but that gets transferred to the inside wheel as well, lifting it upward. The inside spring lengthens, but our "tie it together" part transfers some of this to the outside wheel, pushing it down harder. The result is that the inside wheel doesn't go down as far, and the outside wheel doesn't go up as far. So the car doesn't lean as much.

This keeps the wheels closer to up-and-down, which is a Good Thing for grip generally.

Now, this isn't free. We have increased the load on the outside wheel by pushing it down more, and reduced the load on the inside wheel by pushing it up. The extra load on the one wheel helps grip, but the lighter load on the other wheel hurts grip more. The end result is that the car overall will stick better, but the end with a sway bar will not improve as much as the other end of the car when we add the roll bar!! (Stiffen the front, the rear grips better.)

Yes, if we had a solid axle we would have absolute control over how the wheels lean--but we'd have a crappy ride and any bump in the turn would throw the whole car around. With the sway bar, we've turned our independant suspension into a "mostly independant" suspension.

I hope this helps a bit.

[Edited to fix an "inside/outside" problem.]

--DD
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Old 09-23-2003, 09:11 AM
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Thanks guys. All 3 replies made total sence. I should have been thinking about tire pressure and messing with IT when waiting for my next turn but I just stewed about how unresponsive the car was compared to the way it used to be. I'll concentrate on just having fun.

Also, is there a way to "loosen" a stock sway bar or is that only with adjustable link sway?

bruce
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Old 09-23-2003, 09:39 AM
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Dave - great description, but check your "insides" and "outsides" in your write-up so you don't add confusion.
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Old 09-23-2003, 09:41 AM
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On the subject of tire pressures--most tires have a pressure range where they work the best. I have noticed that many or most normal hard compound street tires like higher pressures, and soft-compound race-type tires like lower ones.

You can play with the balance of the car by letting air pressure out of the one end. (Easier to let air out than add more, particularly out on the road or at an autoX.) Let out ~3 PSI and see if the car's handling changes. If that end of the car grips worse, you know that higher pressures are better. If that end grips better, then you know the lower pressures are working better.

--DD
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Old 09-23-2003, 09:48 AM
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At one point, about in the middle of the left turn sweeper, I had the steering wheel turned to the stop and was not turning as sharply as I thought I should be. (actually, all the fast turns were similar and a few of the slower ones too).
The sideways drift was fun but I had to let off on the throttle to keep from wiping out the cones. I'll try less pressure in the tires.
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Old 09-23-2003, 10:36 AM
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Experimenting with pressures is a pretty good way to go faster without having to spend lots of $$$$. You will need someone to check them for you and I'd recommend checking temps across the tires too since most street alignments are too conservative for hard auto-xing. The previous owner of my race car used to get so much bite he could go up on two wheels at times! At a San Diego session a while back a friend of mine was behind about 0.5 seconds to his main rival. I asked what is pressures were as he was sliding a lot and he said 33# front and rear. So I said try 26# when hot so he did after some convincing on my part and took about 1.5 seconds off his best run during the timed sessions!! Now he believes.
Old 09-23-2003, 11:44 AM
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Bruce, if you are turning the wheel to the stop but the car is not turning enough, that is understeer and is typical of adding a front bar that is stiffer than the rear suspension. Do you know what kind of rear springs you have? It sounds like they are very soft, probably original springs with around an 100# per inch rating that could be much softer due to age and sagging.
If your car understeers after adding a front anti-sway bar you need to stiffen up the back a little bit by installing some 140# springs. They are relatively cheap and easy to install. You could go even stiffer in the back but I wouldn't recommend it with a stock front bar/torsion bars.
Old 09-23-2003, 02:55 PM
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That is just what it feels like Sammy. I was looking at springs this morning on Pelicans web site trying to decide if I should go with just the 140's or go higher. My springs are the stock ones and prolly the originals. Thanks buddy. I let out some air pressure a bit ago and did a test drive.... much better but still has understeer. Gonna get the bigger springs.
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Old 09-23-2003, 03:07 PM
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dave, would you be a guest lecturer for my Physics class? maybe you could steer some of the impressionable high school youths away from the dark side of the rice crowd! polar moment of interia, YEH!!!!! there is no such thing as centrifugal force!!!! (in inertial frames of reference)
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Old 09-23-2003, 03:14 PM
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Quote:
Originally posted by sammyg2
Bruce, if you are turning the wheel to the stop but the car is not turning enough, that is understeer and is typical of adding a front bar that is stiffer than the rear suspension.
It is also typical of turning the wheel too much and getting on the throttle too hard. (Well, if you've got a lot of power to put down then you can use power to kick the rear end out and around...) The point is that it could also be a driving style issue.

Less understeer means more oversteer. That whole "back end is going to pass the front end" feeling.

The key is finding a good balance. If you have a 22mm front sway bar and stock rear springs, you're going to have to work real hard to have a car that does not understeer. But with a stock front sway bar and stock rear springs, you should (which does not always equal "what is" in reality, I know!) have a nice neutral car.

I suggest playing with tire pressures for a little while and seeing what that does for you. If it still understeers too much, go up to 100# rear springs (stock front sway bar and stock torsion bars). Having larger torsion bars in front will make the car understeer more as well.

Oh, and did we mention that alignment plays into things as well??

--DD
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Old 09-23-2003, 04:19 PM
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Quote:
Originally posted by Dave at Pelican Parts

If it still understeers too much, go up to 100# rear springs (stock front sway bar and stock torsion bars). Having larger torsion bars in front will make the car understeer more as well.



--DD
The stock springs are still on the car and aren't those 100#? Dave, do you mean go up to 140's?

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Old 09-23-2003, 09:06 PM
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There is some debate on the spring rate of stock springs. I've heard anything from 60# up to 100 for stock, but I tend to believe they are closer to the 80 range. Problem is, lots of teeners have the OEM springs and they tend to get soft after about 25 years or so.
100# springs might be just right if yours are sagging. Lots of folks here have posted that they really like 140# springs with stock fronts and a stock front sway bar. Do a search, there's plenty of real good posts on that subject.
One other option, you could get a stock rear bar too. I've never driven with one. Some love it, some hate it. Just food for thought.
My last teener had 200# springs in back but it also had a little more weight (and torque)
BTW, I really hate understeer. Yes it's safer and easier to control but it does not fit my driving style at all. I much prefer a small amount of oversteer that I can control with throttle and steering inputs.
A truly balanced car with understeer a little on tight slow corners and oversteer on faster corners, thats where the driving skills come in to play. You need to balance one against the other.
Old 09-24-2003, 04:58 AM
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From what I've read, stock spring rates were 60-70 lbs. I have Weltmeister 100 lbs on my car and the increase in spring rate was noticable, but not a big jump. Ride is not harsh at all with Koni reds. They did raise the ride height noticably though, perhaps 1-1.5", since the originals had sagged after approximately 20 years! I have front and rear sway bars. The combination rides and handles well I think.

Mike
Old 09-24-2003, 05:03 AM
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I saw a set of 110# springs on Ebay. Was thinking of getting those or just grabing some 140's from Pelican. Can't decide! I also have a rear sway ready to install as soon as I get the new bushings from Pelican. Should be here today or tomorrow. I love the ability to over steer a wee bit. It feel like I am the one controling the car instead of the car just deciding not to turn. This last AX I realized I ran with only an 1/8th of a tank of gas when I normally have at least 1/2 to 3/4 of a tank. The less weight in front might have added to my understeer problem, you think?
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Old 09-24-2003, 07:13 AM
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Usually less mass on one end of the car will make that end stick better. (Witness the legendary "tail wagging" of the 911.)

Adding a rear bar will make the car oversteer more. Doing both the springs and the rear bar may be overkill. I personally would just do the springs and not bother with the rear bar. I liked it on my car when the rest of the suspension was completely stock (sagged rear springs and all), but the difference between connected and disconnected was pretty small. When I started upgrading the rest of the suspension, the rear bar was history. Not worth the bother of welding it in, IMHO.

--DD
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Old 09-24-2003, 08:17 AM
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Dave was absolutely correct on a very good point that we should emphasize, alignment and corner balance are critical on these cars and making suspension changes to compensate for a problem with alignment or corner balance will be expensive and may not deliver the desired result.
if you know exactly what set up you want, change the suspension and then do an alignment/balance. If you are diagnosing the handling as is and trying to decide what modifications you want for your paticular needs I would take care of the alignment and balance first.
Old 09-24-2003, 09:00 AM
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As for the alignment, will the addition of the front sway bar create the necessity for a re-alignment? After the sway was installed it felt the same (as far as being straight down the road goes). The car had been aligned by a reputable specialist and re-checked a few times when I had a vibration issue (tires outta balance). Also, if I install new springs will their addition cause need for re-alignment?
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Old 09-24-2003, 10:36 AM
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