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Author Topic: Sway bar settings
Teamfour Verified Driver Made Donation to Website
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I know this has been debated, but a search turns up nothing. Is it possible to set one end of the sway bar to stiff and the other end to soft. What are the pros/cons?

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Lee Tilton
1993 Meowta #04
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Yes, it's like the 'medium' setting.

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It's the same as setting both to the middle setting. Forget left to right, it is the overall stiffness of the bar you are changing. We typically run one soft and one in the middle. Has helped to correct a push we were picking up in the past.

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I've heard that, but I'm not entirely convinced...

The sway bar is a torsion spring. If both sides are set the same, everything is symetrical so push down on one control arm and it pulls up an equal ammount on the other. All the load transfer going into the control arms.

If one side is attached at 1" from the center of the sway bar and the other at 2", one end link gets twice the force of the other. Push down on the 2" side with 100# it creates 200in-lb torsion. The short side pushes up with 200# at a 1" moment arm to create equal torsion in the other direction. That load goes into the control arm. Those forces in the vertical direction aren't equal so they create a moment about the center of the car. The U bracket on the long side must push the body of the car up, and the short side pulls the body of the car down.

[scratchchin]

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I am not an engineer, but the way a very respected race engineer explained it to me was:

You are actually twisting the bar. So when the bars are set different side to side, one side acts as plus, the other as a minus and they balance each other out. That is why you can run asymetrical settings to get an inbetween adjustment. And still have the bar work the same in right and left turns.

When you get really Geeky, there are motion ratios and bushing compliance that do come into effect that will alter L/R movements, but very slightly.

For proof I offer the Roush Trans-Am cars that I work on. The cockpit adjustable sway bars act on one side of the bar only. I figure if it's good enough for Roush, it's good enough for me

Dave

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Dave

For those of us who are engineering challenged.....does setting the 1.6 front bar different on each side make it act like there is no bar?

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Paul McLester

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The other Wheeler is correct. The total is what counts, not what each individual side does.
wheel

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Paul,
It won't make it feel like you have no bar unless you disconnect one side. [Smile]

I was just thinking about other potential things setting both sides differently could change in the way the suspension behaves and it sounds like those other affects are pretty small.

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Davew,

I am an engineer, and I mostly agree with your understanding/explaination. However, I'm sure there are other beliefs out there, some valid, some not.

In my opinion, the sway bar system could be looked at as series of 5 springs. One as a lever arm (the length depending on the hole setting) that is put into bending, the next is a torsional spring between the ninety degree bend in the bar and the first bushing support, the third is a torsional spring between the two bushing supports, the forth is a torsional spring between the second bushing support and the other bend, and the fifth is the remaining lever arm. This is actually a simplified model of what is going on, and it can be simplified further by assuming that the three torsional springs act as a single spring by ignoring the torsional drag of the bushings.

When the car body rolls into a corner, the outside end of the sway bar is pushed down, while the inside is pulled up. This loading puts roughly equal (but opposite) moments into the bar at the two end attachment points. The two "lever arm" portions of the sway bar bend slightly, and the torsional part of the bar is twisted. The torsional spring is relatively softer than the lever arms, so the energy is predominately absorbed by the twisting of the bar.

By placing the end link attachments in "uneven" holes, only gives more adjustment possibilities for the system. Ignoring the small effect of drag at the bushings, the moment forces on the bar are the same on both ends. If the lever arms are unequal due to different positions, the resulting vertical force at each end will be different (force times lever arm on each end will be equal, but in opposite directions).

This is the way I look at the system.

Jerry

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here's the old thread...enjoy.

http://forum.specmiata.com/cgi-bin/ultimatebb.cgi?/topic/42/9.html#000030

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You are overthinking things Keith. It seems (to me) that you think the "flex" is in the arm...and that is where you are wrong. It is the torsion of the bar that adds the load, not the flex of the "bent" arms. Go grab a little bitty 94 stock swaybar and try it...you will understand it easier.

Another way to think about it is...Think of a 3 piece swaybar with those big end pieces on an indexed rod. I assure you that those end pieces aren't flexing....the rod is twisting.

Tracy Ramsey
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I do understand how the torsion in the bar ties the motion of the control arms together. The stiffer the spring, the less the rhs and lhs want to move in opposite directions.

Someone told me one day that it would stiffen one side more than the other. I argued a bit. They said, "Do the math." I couldn't be bothered with arguing and went back to screwing with my car. Bored much later, I played with the math a little bit and noticed some other things going on. Hard to explain without a sketch.

Apparently it's not enough to make much difference. I played with numbers just long enough to figure out things didn't work exactly the same but not enough to say how much a difference there really is... And yes I'm definately overthinking it but I do that sometimes. [Razz]

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AG great link. I am not a math major or physics guru.....so does using different front bar or rear bar settings make a medium setting and do you use the front hole on a certain side for certain corners (i.e. front hole, left side for right hand turns?)

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Paul McLester

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The difference, from side to side, is only equal to the amount of friction resistance in the bushings that support the bar. With totally frictionless bushings, there will be no difference in the effectiveness of the bar, from side to side. So, no, you won't get any asymmetrical benefit from having one side in one hole and the other side in a different hole. At least, not enough to make a difference.

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wheel is right for a Miata. But in a "real" racecar there actually is a difference.

In a Trans Am car, very stiff chassis, no rubber bushings and a 2" sway bar, there actually is a noticable difference side to side. The latest generations adjust both sides of the sway bar with a single cockpit adjustment.

As soon as you add rubber bushings into the suspension, all the differences are absorbed by the bushings. Therfore, you will not notice the left/right difference in an asymetrical sway bar adjustment in one of our cars.

My baseline setting for the front of a 1.6 is soft/soft. Since most drivers induce a push with too much corner entry speed. For the rear I start middle/middle. Then adjust one side at a time for driving style or track conditions.

I generally adjust the right side. Driver weight on the left side requires the driver to be in the car for adjustment. Driver weight does not effect the right rear corner that much. So I do not have to re-zero the bar if I only adjust the right rear.

Dave
not an engineer, but a good listener

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quote:
Originally posted by Gatoratty:
AG great link. I am not a math major or physics guru.....so does using different front bar or rear bar settings make a medium setting and do you use the front hole on a certain side for certain corners (i.e. front hole, left side for right hand turns?)

Paul- Using different holes on each side will make your setting somewhere between those two holes. Stiff on one side and medium on the other will make it medium/stiff. Stiff and soft will make it mediumish. Maybe not the same as meduim/medium but stiffer than soft and softer than stiff.

Aside from what Dave points out (and some side affects I may explore when I get bored again) it doesn't matter which side you set stiffer or softer. It's just about how much the bar twists.

You can kind of think of it like a progressive coil spring where the coils are tighter on one end than the other. One end of the coil spring is stiffer than the other end. Squeeze the spring by a given amount and it will compress a given amount. Turn the spring around the other way and it does the same thing.

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Thanks guys!

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Paul McLester

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That was a lot less painful than I thought it was going to be when I started reading the thead! The rest of the engineers must be working.
Rick

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Thanks! This was much more understandable then the older link referred to earlier.

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Lee Tilton
1993 Meowta #04
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So here's my 2 cents on the subject. I do this stuff for a living on a NASCAR team as a Vehicle Dynamics Engineer, but by no means claim to be the next Carroll Smith.

Think of the suspension inputs to the anti-roll bar in two ways... Ride Motion and Roll Motion.

In Ride Motion, when both wheels travel equal amounts, the side with the shorter arm length (ie. rearward most hole on the rear bar), will twist the bar a greater amount than the side with the longer arm length. As a result, the bar will actually induce roll towards the side with the longer (softer) arm length with a pure vertical "Ride Motion" input.

In Roll Motion, assuming that the left and right travels are equal and opposite, meaning for roll in a right hand turn, the left side moves into jounce 1" and the right side moves toward rebound 1", then the torque build in the bar is exactly the same if you run the left side soft and right side stiff, or vice versa. Since the length of arm to each side is different, however, the side with the shorter arm is resisted with a greater vertical force than the long arm side. Think of it as putting a slightly higher rate spring on the short side and slightly softer spring on the long side.

In reality, the loads for any typical turn on a road course will induce a combination of ride and roll motion so that the left and right sides will not have equal and opposite jounce and rebound travels. Aerodynamic downforce and roadway camber both induce vertical travel (Ride Motion) in the jounce direction, which means that the car will be subjected to unequal suspension roll forces based on left and right hand turns. Non-typical turns that are significantly off camber (ie. Turn 3 at Grattan) or on the downside of a hill crest (ie. VIR Turn 9) can put the suspension in rebound, which will reverse the Ride Motion effect of bar assymetry, reversing some of the roll effect.

Most people neutralize their bars with driver's weight at the static condition, and "jounce" and "rebound" travels are relative to that static position.


TileySpeed guide to Front & Rear Sway Bar Assymetry (for "typical" turns)

Front Bars (in order from Max to Min understeer on right hand turns)
  • Left Short, Right Short: Maximum front roll stiffness. Max understeer on lefts and rights
  • Left Short, Right Long: More understeer on rights than lefts
  • Left Long, Right Short: More understeer on lefts than rights
  • Left Long, Right Long: Minimum front roll stiffness, Minimum understeer effect on lefts and rights
Rear Bars (in order from Max to Min oversteer on right hand turns)
  • Left Short, Right Short: Maximum rear roll stiffness, Max oversteer on lefts and rights
  • Left Long, Right Short: More oversteer on lefts than rights
  • Left Short, Right Long: More oversteer on rights than lefts
  • Left Long, Right Long: Minimum rear roll stiffness. Min oversteer effect on lefts and rights

Side Note... while anti-roll bars reduce the amount of roll, thus helping to maintain camber and CG heights, they increase the rate at which load transfers from the inside wheel to the outside wheel in a turn, lessening the usage of the inside tire. They're a great tuning tool to help balance a car, but stiffening a bar actually removes total available grip from the axle that is working in order to balance it with the one that is not. Often times, camber, toe, and/or tire pressure can be used instead to help improve the grip on the axle that isn't working as an alternative, resulting in greater total available grip.

So much for 2 cents.... this turned into a book!

[ 11-19-2009, 08:21 PM: Message edited by: Dan Tiley ]

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quote:
Originally posted by Dan Tiley:
As a result, the bar will actually induce roll towards the side with the longer (softer) arm length with a pure vertical "Ride Motion" input.

Thanks! You just helped explain and put a name to the sketches I was toying with on the induced roll affect. I will now tuck those sketches safely away in my round file and ponder it no more. [thumbsup]

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quote:
Originally posted by Dan Tiley:
TileySpeed guide to Front & Rear Sway Bar Assymetry (for "typical" turns)

Front Bars (in order from Max to Min understeer on right hand turns)
  • Left Short, Right Short: Maximum front roll stiffness. Max understeer on lefts and rights
  • Left Short, Right Long: More understeer on rights than lefts
  • Left Long, Right Short: More understeer on lefts than rights
  • Left Long, Right Long: Minimum front roll stiffness, Minimum understeer effect on lefts and rights
Rear Bars (in order from Max to Min oversteer on right hand turns)
  • Left Short, Right Short: Maximum rear roll stiffness, Max oversteer on lefts and rights
  • Left Long, Right Short: More oversteer on lefts than rights
  • Left Short, Right Long: More oversteer on rights than lefts
  • Left Long, Right Long: Minimum rear roll stiffness. Min oversteer effect on lefts and rights


Dan
These are my thoughts exactly, started a post and realized how long it would be, then 14 counter posts and decided not to [Big Grin] Great explanation.
Jim

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Dan

Thank you for the easy to use chart! [Smile]

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Paul McLester

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No problem... I hope it's helpful to all! BTW... I made an edit to the Roll Motion explanation, but this did not affect the chart.

Perhaps one of our site admins can slip this chart into the FAQ section?

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Dan is the man, he is the engineer for Richard Petty Racing and has been a major reason for the success that Kasey Kane has been having. [yep]

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Lee,
There is a lot of good advise here and good racers .
Study your tire temps , once you understand the temp . They will be a lot of help, in your adjustments.

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Looking at Dan's chart, and his "ride motion" explanation, I realize that, even racing for 33 years, there is always something new to be learned.
wheel

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I haven't had my first SM race and I'm behind the curve already. Great explanation, nice chart. Now for me to wrap my brain around it and really understand the dynamics....

Tracy Ramsey
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Tracy Ramsey
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Dan, how much power do those Petty cars make? [rolling on floor laughin] [rolling on floor laughin]

Sorry Guys inside joke. [Big Grin]

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Not as much as the 48 car. [rolling on floor laughin]

Pat

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quote:
Originally posted by pat slattery:
Not as much as the 48 car. [rolling on floor laughin]

Pat

Ain't that the truth?!?!

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quote:
Originally posted by pat slattery:
Not as much as the 48 car. [rolling on floor laughin]

Pat

The 48 car is a 99 [duck]

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I have a 99, Are there any advantages to running with the rear sway bar disconnected???

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Scott,
Disconnecting the rear bar is commonly done when it's wet enough to have standing water on the track.

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Keith Novak
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^^ and on certain tracks with constant curve long corners where slow progressive weight transfer helps to maintain tire contact.

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I never unhook the rear bar except in rain. My opinion is unhooking the rear bar is last ditch effort to "fix" an ill handling race car with an unknown problem. Most likely unhooking masks whatever the real handling problem is at best. I don't doubt it feels better by stop watch and feel, but still doubt it is the "right" answer and that the car would be faster and feel better with bar attached and real issue rectified.
Jim

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Jim,

My car severely oversteers with the sway bar attached. I have tried it on different settings but continue to have the problem.

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Scott,

Check the simple things like making sure the front and rear springs are not reversed. Get the car level, off the bump stops and corner weighted. Check camber and toe setting. If all of this is within spec there is another problem with the car that needs to be sorted out. Good luck.

Jim or others may have some thoughts to offer as well.

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Scott
Miatas are such good handling cars as it is, you have an issue. Did you read he setup guide? I am not sure what your problem is but you should check all first, ride heights, rear bar binding, etc. if you want to give me a call, I will see if I can help 901 647 1700
Jim

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After reading and studying the above I have a question that wasn't asked.

When I sit the front sway bar on the ground one arm is a good half an inch off the ground
compared to the other side. The remainder of the bar is level and straight in all directions. Having never seen a new in the box one,I ask:

Is this normal or do I have a bent bar?

While I realize it can be straightened, would it hold or revert back to the bend under the first serious load exerted upon it?

Thanks,
Jim

Keith in WA Verified Driver Made Donation to Website
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It sounds like your floor isn't level. [Smile]

Seriously though I wouldn't worry about it. Each end doesn't have to be in an exact position as long as they can swing through the full range of motion. One end will be 1/4 inch lower and one will be 1/4 inch higher in the neutral position.

I also wouldn't worry it bending more. That type of steel can flex quite a bit before it takes a permanent bend. I'd be willing to bet that the designers made sure that the bar can twist more before it takes that set than the suspension can move.

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Keith Novak
(Will work for tires)

Howard
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With all the brain power here maybe someone can help a rookie. I found out what happens when the front bar is disconnected when the bolt connecting the swaybar to the linkage fell out on the track. Sure surprised me in the next turn! The stock links have a rubber bushing at each end and I assume should be bolted in tight enough that there is no rotation between the link and the sway bar - correct? Does the resistance of the rubber mount in the linkage flexing have an effect on the whole system? I've been thinking of installing some of the adjustable linkages available but they don't seem to have the rubber bushing. Good or bad?

Howard

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Actually the ends of those links should be able to rotate freely. That ensures that the link itself is only loaded in tension or compression and doesn't cause any twisting at the attachment points or in the link itself which could cause it to bend or snap.

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Keith Novak
(Will work for tires)

Howard
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Keith

I don't see how this is possible with the stock links. The mounting hole in the sway bar would have to act as the bearing surface. Wouldn't this evenually enlarge the hole causing it to wear out and fail - not to mention a lot of play in the system? I found out the hard way that the bolts can't be left loose enough to rotate. They fall out. Are the adjustable linkages the way to go?

Howard

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The stock end links are just cheap. They aren't ideal at all. Then again the stock sway bars aren't nearly as beefy as the SM kit so they don't really need to be.

The adjustable end links are definately better. Rod end bearings (heim joints) like you find on the adjustable links are much more expensive to make though. They result in less stress on the links and also into the connection ponts. It's a standard type of connection used in all types of mechanical engineering to transfer a lot of load in a controlled direction without using a ton or material to reinforce things.

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Keith Novak
(Will work for tires)

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You'll really need adjustable links to get rid of any preload when corner aligning/corner wheighting. Pretty much mandatory for any type of repeatable tuning.

-b

--------------------
Bruce Wilson
2010 Oregon Region Champ
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any recomendations on which ones to buy?

   

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