Sway bar vs air bag

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Post by BillyShope » Wed Aug 23, 2006 1:48 pm

Ed-vancedEngines wrote: Both of these mythical cars have existed and have been tried for years.
Again, the "cars" I described do not and never have existed. They were used merely to describe the limiting conditions. By understanding the performance of a system at the limits, it is then possible to interpolate and determine the most likely performance at an intermediate condition.

Similarly, if you adjust the instant center to lie above the no squat/no rise line, the car will rise on launch. If adjusted below, it will squat. If follows that, at some intermediate point, it will neither squat nor rise. This does not require a "solid" suspension.

If I stated that video studies of a launch can produce NO useful results, I misspoke. I will state that this is an extremely wasteful procedure when a traction dyno can reproduce the launch conditions far, FAR better than any frame-by-frame video analysis.

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Post by Ed-vancedEngines » Wed Aug 23, 2006 2:48 pm

Hey Mr Billy,
I will concede about the no aquat/no rise line at times called the neutral line, if you will think about that the theoretical neutral line must then need to be moved according to the amount of torque/power than is in the car. I will not concede that we do not need any additional force pressing against the rear tires than what the car would have at rest though.

We do need a quick and not too hard of a hit in planting the tires and we do need to maintain a stady pressure downward on the tire all through the gear and when the shift is completed that again this cycle on a smaller scale needs to continue in a downward pressing of the tire toward the track surface.

The only car that can work with the instant center actually placed in the middle of the theoretical neutral line is a low torque small block. I have done that and it worked well. I have also placed a bigger engine in that same car with the same suspension bar positions and the car hit the tires so hard it bounced all four wheels into the air. That same car ended up needing the instant center to be placed 4 inches below the ground and back to 40 inches from the rear axle . Now by all of the expert theories that car would have surely been squatting on the launch but was not. It still was planting the tires with close to two inches of chassis separation. Called antisquat.

May I ask you something please that I can not understand?
You seem to be an older person. If you were with the RamCharger Team you must be an older person. I keep wondering why you are using terminology that was started by Chris Alston many many years since the RamCharger Team quit racing. The anti-squat and Anti-rise and Percentage of rise theories began with the Alston Engineering Chassis Clinics.

The old "imaginary Line" way of looking at things has existed from day one of the first Ness 4 links. The old Butler 4 links that were tried previously all had the bottom bar in an uphill position with the instnat centers very high and hit the tires very hard. Do you also remember the Ladder Link set up that was used by several of the Mopar Teams? That one also had a tire jerking high instant center. Not until Don Ness began installing his version of a 4 link did anyone to my knowledge consider lowering the point of instant center.

I still use the old "Imaginary Line" theory as my reference of which way the instant center needs to go and guess what -- it works as welll as it always has when used with experience and knowledge.

I can guarantee that any of todays ultra high horsepower cars would experience major tire hit if adjusted to the theoretical 100% Percentage of Rise position anywhere on the Theoretical Nutral Line or the no rise/no aquat line.

Comprehend horsepower like was only in Dragsters in the early years but it is now in cars with full suspensions and more weight.
Ed

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Post by BillyShope » Wed Aug 23, 2006 8:56 pm

Ed-vancedEngines wrote:Hey Mr Billy,
I will concede about the no aquat/no rise line at times called the neutral line, if you will think about that the theoretical neutral line must then need to be moved according to the amount of torque/power than is in the car.
The position of the no squat/no rise line is not affected by the forces involved. It becomes meaningless, however, as soon as the front tires leave the strip surface.
Ed-vancedEngines wrote:I will not concede that we do not need any additional force pressing against the rear tires than what the car would have at rest though.
Don't know how you could conclude that I had said this. If the car is accelerating, there will be an inertial force which will increase rear tire loading.
Ed-vancedEngines wrote:We do need a quick and not too hard of a hit in planting the tires...
What do you mean by "a hit"? As I just said, if the car is accelerating forward, rear tire loading is increased over static. Are you referring to the rear of the car accelerating downward? All this does is provide an oscillatory loading of the rear tires. The loading is reduced as the rear is accelerated down and then increased as the rear reaches its lowest point. It's very questionable that the net result would ever be beneficial. Certainly, a rising rear would appear to be better, for shock absorber action and friction quickly dampen these oscillatory loadings.
Ed-vancedEngines wrote:The only car that can work with the instant center actually placed in the middle of the theoretical neutral line...
Don't understand "in the middle." If the instant center falls anywhere on the no squat/no rise line, the car will neither squat nor rise.
Ed-vancedEngines wrote:Now by all of the expert theories that car would have surely been squatting on the launch but was not.
In the first place, engineers do not work with "theories." Theories are in the domain of scientists. It is only after they've done their thing and used the "scientific method" to transform their theory into established science that the engineer is allowed to enter the picture.

Your comments here cause me to believe that we're not talking about the same line. The no squat/no rise line passes through the rear tire patch, when viewed from the side, and the intersection of two other lines: one a horizontal line through the center of gravity and the other a vertical line through the front tire patch. The instant center is determined by finding the intersection of lines through the upper and lower links.
Ed-vancedEngines wrote:May I ask you something please that I can not understand?
You seem to be an older person. If you were with the RamCharger Team you must be an older person. I keep wondering why you are using terminology that was started by Chris Alston many many years since the RamCharger Team quit racing. The anti-squat and Anti-rise and Percentage of rise theories began with the Alston Engineering Chassis Clinics.
Yes, I'm long of tooth. You appear to be familiar with God's Word, so I'll simply say that I'm beyond the alloted "three score and ten" and every day is now by God's grace.

I was taught of the "no squat/no rise line" during my graduate studies. I don't know if Alston is claiming to be the originator of such matters, but that would be like Al Gore claiming that he invented the Internet. For that matter, any competent engineer of the nineteenth century, given the problem of a buggy driven by the rear wheels, would have come up with the same line. As the Spirit guided Solomon to write, there's nothing new under the sun.

(It appears that Chrysler refers to the line as the "no squat/no rise" line, while Ford and GM refer to it as the "100% anti-squat" line. Same thing.)

Ed-vancedEngines

Post by Ed-vancedEngines » Wed Aug 23, 2006 9:29 pm

Mr Billy,
I enjoyed the humor you included into this response. I am 60 so you have been around the block a little longer than I.

Please do not think that in my responses to your ideas and in my responses to you that I am wanting to be argumentive or to be dis-respectful to you sir.

I do like your idea of the Traction Dyno and also quite a lot of the things you have freely shared. I just am not a person who agrees with things to just agree or because the person I am not in agreement with is smarter than I. I have no education so I sure do not speak from any form of formal education. That has nothing to do with all of my mis-spelled words though. Actually I am very godd at spelling I just can't type or seem to hit the correct keys, plus it seems as I am getting older that words are spelled correct in my head but are written with letyters out of place.

I do not think that Mr Chris coined the exact words of no squat or no rise. He did begin the usage to my knowledge of figuring suspensions by using a Percentage of Rise calculation and did use the words of Anti-Squat in his seminars.

When I speak of the imaginary line or speak of it as the line of theoretical Instant Center, I am speaking of the imaginary line from center of tire patch that will run diagonally to the actual center of gravity of the car at the balance point.

I use this line only as a reference in my mind, nothing else. In my little mini-seminar page I suggest for those reading it to maybe use a piece of tape taped to their car in that diagonal configuration so they can look at it visually and see what is taking place when they move a ladder bar attaching point or a 4 link Instant Center, in relation to that imaginary line.

What I call the Active Instant Center or at times simply Instant Center is the point of intersection of two imaginary lines stretching along each of the two bars, top and bottom while the car is at rest and fully loaded with all weight in place.

The term Hit is a recent term used down here in Texas at least when guys are talking about how the tire is reacting. In my words of old school we called it chassis separation or in the words from Alston's seminars he called it Anti-Squat. the meaning is about how much the tire is forced to the pavement by suspension reaction. Usually this is seen on the frame by frame as a separation in the distance of the top of wheel from the bottom of the fender lip. I see it very often that the distance or amount of separation or Hit is too extreme in my opinion. It can end up like the old Pinion Snubber reactions. I am sure you know what I mean.

I am 60 or close to it or over it, who knows or cares but I do still love to learn.

So pleae I ask for a little temperance when reading my responses to you sir.
Ed

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Post by BillyShope » Thu Aug 24, 2006 8:40 am

A line from the rear tire patch to the center of gravity is, for our purposes, of little value.

As the car is accelerated forward, the summation of inertial forces can be considered as a single force acting at the center of gravity and with a direction opposite to that of the acceleration. (The inertial force is proportional to the product of the acceleration and mass, so it is not necessary to consider specific values for either.) An equal and opposite horizontal force is acting at the rear tire patch. Since these two forces are displaced vertically by the height of the center of gravity, a torque is developed. This would be, when viewed from the passenger side, counter clockwise in direction. Now, unless the car is about to do a blowover, there must exist a clockwise torque of equal magnitude. This would be developed by the vertical forces acting at the front and rear tire patches. At the rear, the force is increased by what is called the "weight transfer." At the front, the force is decreased, resulting in the rise of the front which we expect. Since the product of the center of gravity height and the horizontal force acting at the rear tire patch must equal the product of the weight transfer and the wheelbase, we can say that the ratio of weight transfer to tire patch force must equal the ratio of CG height to wheelbase. This is also the slope of the no squat/no rise line. But, I'm getting ahead of myself.

In the force and moment (torque) balance described in the preceding paragraph, I considered only those "new" forces and moments which occurred due to the acceleration. All of the static forces and moments were already balanced, so it was not necessary to include them.

The weight transfer can be carried to the rear tire patch entirely through the suspension linkage or partially through the linkage and partially through the suspension springs. If it is carried entirely through the linkage, there will be no compression or extension of the springs. If the linkage does not carry the full load, the springs will either compress (squat) or extend (rise).

Since I'm attempting to define the no squat/no rise line, I will assume that all of the weight transfer is taken through the suspension linkage.

Now, I'll make a couple of assumptions to make things easier for me. Neither assumption is of great significance and both will be resolved before I'm done. First, I'll assume that the weight of the rear axle assembly is negligible (zero) compared to the weight of the rest of the car. Finally, I'll assume that the rear axle assembly is connected to the rest of the car by ladder bars.

I'm now going to attach the ladder bars at some "crazy" points. The first crazy attachment point will be at the rear tire patch. Yes, that's impossible, but, if it were possible, the forces at the pivot will be those forces we've already determined. The second crazy attachment point will be at the intersection of two lines: one a horizontal line through the CG and the other a vertical line through the front tire patch. Again, it should be evident that the forces at the ladder bar pivot will be those forces already determined. The horizontal component now lines up with the inertial force acting through the CG and the vertical component now lines up with the unloading force acting at the front tire patch. The no squat/no rise line passes through these two crazy points.

Back to the assumption of a weightless rear axle assembly: Part of the rear tire forward thrust is used to accelerate the mass of the rear axle assembly. The effect is to displace the no squat/no rise line downward by a distance equal to the rear tire radius multiplied by the ratio of the rear axle assembly weight to the weight of the remainder of the car. This is usually somewhere between one and one and a half inches. Most textbooks ignore this effect and illustrate the line as passing through the rear tire patch.

Now, the ladder bar assumption: If you were to extend the upper and lower links of a 4link, they eventually would meet and you could use a single Heim as a pivot. And, of course, you end up with a ladder bar. This is the idea behind the "instant center." Instantaneously (before any squat or rise or bumps in the strip surface can change things), the 4link acts like a ladder bar with its forward pivot at the instant center.

But, what if the horizontal and vertical force components, at the pivot of the ladder bar, are not located on the no squat/no rise line? Suppose, for instance, that the pivot is above the line. In that case, the product of the vertical distance between pivot and CG and the inertial force would be less than the product of weight transfer and wheelbase. In other words, the clockwise torque would be greater than the counter clockwise torque. To make up the difference, the rear springs extend (rise) until balance is achieved.

Hadn't planned on such a long post, but I'd probably end up saying the same things in a number of short posts. I think I'll add this to my blog.

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Post by Silverback » Tue Jul 15, 2008 3:19 pm

You know, for some reason I ran across this again and reread the whole thing and realized that we really don’t have an answer to the question here.

2 years later it seems like more so than back then dragrace style antisway bars are preferred to air bags or other means of preload, but I don’t really see a reason for it or for them to work better.

Safety is the biggest answer in this thread, but I don’t really see an airbag or it’s related plumbing popping/leaking being any more likely with a careful install than a sway bar mount or more likely endlink breaking (I’ve broken at least 3 passenger side rear endlinks over the years, I’ve never ruined an air bag or air bag air line, maybe that’s just my own dumb luck).

There is some implication that when you let off at the big end of the track you will get a counter steer from the different preload side to side which will attempt to steer the car to the side… while I can see that, I don’t see why it should be any worse with air bags vs a preloaded sway bar, the preload on the passenger side should be the same amount whether you do it with the sway bar or spring (air bag in a spring).

While the rest of the discussion is interesting and even approaches a true kinematic discussion of what it happening during a launch, but I’m not sure that it amounts to much more than a discussion of the basic geometry problem and how it applies to theory/engineering, and in this case does apply to a purpose built car, but not to the “fast street car” that the question is about. The fact is that this car will not have a perfect straight line suspension or chassis; it will be crippled by a real world street car suspension which as far as I can tell forces you to deal with some form of adjustable preload to get the car down the track fast and reasonably safely.
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Post by BillyShope » Tue Jul 15, 2008 4:12 pm

Yes, the thread got sidetracked somewhere along the way.

Any form of static preload will work, but it will always be a very poor substitute for dynamic cancellation of the driveshaft torque. A dynamic setup can fully cancel the driveshaft torque's tendency to unload the right rear tire. See my site for a full explanation and examples.
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Re: Sway bar vs air bag

Post by n2xlr8n » Thu Aug 04, 2016 3:57 pm

Bump a thread so I can find it again :D
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Re: Sway bar vs air bag

Post by F-BIRD'88 » Thu Aug 04, 2016 7:18 pm

If you are so worried about the right left rear air bag pressure difference upsetting the car upon deceleration at the end or during a upset why no just dump the bag pressure with a solenoid in the air line during the pas after launch.
Having a bag burst or a air line blow during a run is very unlikely unless the install is very flawed. It is much more likely a suspension or sway bar part will fail especially if preloaded and or binding from the preload.

When setting up the suspension remember it is a 1/4 mile trip.
The car still has to handle well at high speed, especially if it does get loose.
The higher the power and speed the more likely and the more sever the
result may be.

Leave both sway bars on the car. If the car needs a ton of preload bias rethink it.

Also TEST the car during a emergency stop event to see what it is going to do.
every action is going to create a equal and opposite reaction.

Preload for equal launch will have the opposite effect on hard deceleration
and or car sway event loss of traction at high speed "gets loose".

If it is a street driven car keep it real.

The higher the car speed the MORE stability you want. Areodynamic loading can be your friend or enemy beyond 140MPH.

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