View Full Version : Adjustable Blade Anti-Sway Arms ???

02-11-2006, 06:07 AM
Hello everyone. Just wondering if anyone could help me out here. I am an automotive engineering degree student and as part of a design project I would like to model adjustable blade sway arms in conjunction with a interchangable hollow sway bar (the type similar to those used in stock car racing) for a touring car application. To give you and idea of what I am talking about I have found only a few actual applications of this design on the web and have included the links below. Now I know it may be all "theoretical" but I have to treat the project as something real and design a working solution with real calculations, data etc. Preferably I would be interested in sway bars that are adjustable by the technician during a pitstop i.e. have to be adjustable in seconds.
Does anyone have any experience with adjustable blade type sway bar arms? Can anyone offer any help, advice or recommend literature on this type of anti-sway system. Any help offered would be greatly appreciated.


02-11-2006, 09:25 AM
It is not just a matter of studing the sway bar in a touring car aplication. A sway bar is a tool. A tool does not know what it is being used for. You need to have an understanding of the materials involved to understand how it works. Being an automotive engineering student a good reference of metalergy would do you good. That would give you more insite in to how the adjustable sway bar works. But hear is a quick discription of how it works. The main tube is your maximum posible stifness. The blades are shaped in that fashion to put mor give into the system or soften the efects of the bar. The blade starts in a vertical posision or on edge, that is applying +100% of the sway bars power to the suspension. As you rotate the blade to a flat position the material gets thinner and adds flex to the system ther for reducing the overall strength of the bar being used. Some of the vertical forces being applied to it from the suspension are absorbed into the blades. You can not actually adjust the sway bar itself. You cannot adjust the metal of the bar so you have to change the amount of force that gets to the bar.

Someone else may come along and say I am completely wrong and I may be. I am not an engineer by any meens. Every thing I stated is from my own first hand expieriance and self studies. I have been racing since I was a little kid. It does not matter how big or little the peices are physics and math don't change.

Norm Peterson
02-11-2006, 10:09 AM
Actually that's a fairly accurate description of how it works.

In a little more structural detail, the stiffness of a sta-bar can be expressed as the sum total of a whole collection of individual stiffness terms, and the stiffness of the assembly (the bar) is the result of springs-in-series math. Or more simply, by working with flexibilities and a simple summation of same before taking the reciprocal.

Simplified a bit, most of the flexibility in any sta-bar comes from twist in the central torsional section and bending in the arms. What the blade adjusters do is vary the flexibility of the arms, so all you need to know in order to plot a curve of bar stiffness vs arm adjustment is the stiffness (flexibility) of the arms at various points of adjustment and the torsional stiffness of the center section. Being pickier would include one or more of the "little" effects.

Actually, it isn't particularly difficult to make such sta-bar adjustments possible from the driver's seat, assuming that there is no rule prohibiting it.


02-11-2006, 10:21 AM
Ill post a short response. I think this would be cool. But as far as how often it would be used im not so sure. Swaybars for me are the last think I figure when building a chassis. So, it works with the springs, shocks, and other suspension components. Im not sure if I would ever have to change it on the fly. Keep us updated.


02-11-2006, 02:04 PM
Norm and track have it. From an engineering perspective the deflection of the blade is a simple beam deflection calculation. However, as the blade rotates the effective moment of inertia of the blade changes. From a theoretical standpoint, the stiffest cross-section is an I-beam when loaded in parrallel and in-line to the web. If the loading angle is changed, the effective MOI changes, and the beam will deflect more.

Another, easier way to think about it is to take a sheet of 3/4" thick plywood and carry it flat. It's very weak. Turn it on end and it is very strong. MOI is based on the distance from the bending axis to the outermost fiber. On the sheet of plywood carried flat that distance is 3/8". When it is carried on end it is 24". It gets more complicated due to materials and exponentials, but that's where your research comes into play.

02-11-2006, 04:06 PM
I believe ATS is coming out with just what is being talked about here. I wonder if Shane or Tyler would like to pop in and show off a little. In fact, I'd be interested in one for my '77 Camaro. Hell, I may just do it with a stock car bar.

02-11-2006, 05:12 PM
Hey Folks,
Thanks a whole lot for the posts so far. How these bars work makes perfect sense and that is why I am interested in this simple but effective system. I must say that prior to studying I was a Automotive Technician (what am I talking about, I still am a mechanic at heart :o) ) but this is like specialized racing stuff that you don't find on "normal" passenger road vehicles. I have never heard of these rotary blade type adjustable sway bars on stock cars.
Now for the folks who have experience with such blades, a valid point was made earlier by trackrat79 about materials. I am thinking along the lines of Aluminum alloys for the blades. I'm thinking about overall weight, cause I wanna get that bar as light as possible in the design but still need the strength. I am concerned about the fatigue that may be displayed by the part over extended use. Any other suggestions for realistic materials? I will have to check them out with a Materials expert before I can start designing and all the spreadsheet calculations associated with this stuff.
Since I am not from the "scene" who is ATS that zbugger mentioned?

David Pozzi
02-11-2006, 06:34 PM
I'd like to install one on my wife's car (rear bar) but I'm not up to doing the math to figure it all out.

The adjustable arm should have a triangular shape but the taper needs to be such that the arm bends uniformly throughout it's length.

I've heard of the arms bending sideways when adjusted half-way, giving unpredictable results. Rault used guides on the ends to prevent this from happening, now such formula cars use T bars.

If you look at the Cobra arm in the first link given, that one goes way too soft when full soft. I don't see much use for an arm that can go from 100% to 20%.

I'm flat guessing that at full soft you'd want something like 10% or 15% loss of the total bar rate, at least for the rear of a Camaro. Most of these adj bars are used to compensate for substantial fuel burn-off. A Trans Am car carries something like 40 gallons (260lbs) of fuel just behind the rear axle! Many of them have adjustable front and rear bars, but only one side is adjustable.

Someone sells an adjustable bar for a Mustang with toggle switch control. I think a servo for aircraft trim might work, or there are cable adjusters.

I'd stick with steel for material. Maybe Titanium if you want to get fancy. Aluminum just isn't going to have enough spring. Go with a hollow bar for less weight.

02-11-2006, 06:40 PM
Since I am not from the "scene" who is ATS that zbugger mentioned?

ATS is American Touring Specialties. Their website is www.t56kit.com (but it's not current) or their usernames around here are Teetoe Jones, wickedmotorhead, and a couple of others I can't remember off the top of my head.

02-12-2006, 05:21 AM
Thank you David for those valid points concerning material selection, arm profile etc.
You mentioned Rault using guided arm ends to prevent bending of the arms. Good stuff. Do you know how I can get in touch with Rault or if they have a webiste?

Any other known manufacturers of adjustable blade type sway bar arms? Where or who would you go to if you wanted to get your hands on such a piece of equipment?

02-12-2006, 08:36 AM
If you must run something other than steel your best bet is probly carbon fiber. As was stated before aluminum would not be a good choice as the blade mite just bend when turned on its side as the thickness of the material gets thinner. I am not sure about titanium. I was under the impresion that titanium is strong to a point but very brital. I have seen carbon fiber ones so I know it will work, I wish I had specs of the actual blades to give you.

David Pozzi
02-12-2006, 10:29 AM
Here's a formula.
Race Car Engineering by Warren J Rowley is a good source for info. http://www.rowleyrace.com/

Most blades don't have guides but Rault felt they were needed on their Indy cars. Suspension movement on an Indy car (at Indy) can be as low as 1/4", so everything counts in that application.

02-13-2006, 12:59 AM
Thanks trackrat79 and David. Excellent. Will be following up those ideas and leads... hopefully when I get it done I can post a pic of what I modelled.

Thanks again for all your help.

02-15-2006, 06:46 PM
Something nobody else mentioned is a coupling device between the two halves of the swaybar. American Axle and Manufacturing (make the axles, driveshafts, suspension forgings and other parts for GM, Dodge, etc) introduced a swaybar for the H3 Hummer I believe (could also be the Dodge Power Wagon) that is able to switched on and off. When you go off road, the bar is switched off so the wheels can fully articulate. The switching is done at the middle of the bar with a remote controlled locking mechanism. Basically, they can detach one side from the other eliminating the affects of the bar.

While this system is purely on/off, it wouldn't take much to make it adjustable. Think about joining the two halves of the bar with a spring. By changing the preload on the spring, you would change the bar rate in the same manner as twisting the bars mentioned in the other posts. If you really wanted to get trick, you could use a viscous coupling filled with the same fluid that's used in modern adjustable shocks. The fluid has metal particles in it, and it's viscosity can be changed by applying a magnetic field. Being an automotive engineer myself, this kind of mechanism is a little mroe cutting edge. The adjustable mechanisms described in the other posts are great because they are simple and work, but they don't take advantage of the awesome microprocessor power available. With an adjustable viscous coupling, you could adjust the sway bar rate for anything: road conditions, fuel load, passengers, tire pressure, anything.

Something to think about.

Norm Peterson
02-16-2006, 05:23 AM
I think BMW has also used a switchable front sta-bar, presumably of similar design (645 models?).

You'd need to be able to change the rate of any spring separating the bar halves, not its preload, in order to effect a variable-rate adjustment for the bar as a whole. Mathematically, this adds yet another "spring in series" to the mix that's flexible enough to have a meaningful overall effect. A preload setting would only affect the location of the "knee" point in a bi-linear load-deflection curve, not the rate on either side of such point. You might be able to ultimately get to the same point (in terms of load and deflection) either way, but the bi-linear path would likely not "feel" as secure as you pass through the knee.

Off the top of my head, providing infinitely variable adjustment over some range in something that looks anything like a conventional bar (read: will fit in generally the same space) involves moving something to vary either the lengths of members in torsion or the inertias of elements in bending.

I'm not at all sure that a magnetic fluid connection is going to do what you want from a sta-bar, unless the intent is to provide really heavy damping in roll as such motion is in progress rather than by adding any additional roll spring stiffness that limits the amount of roll ultimately developed at some lateral acceleration. Unless there's something about this fluid that I am unaware of, a fluid device only offers resistance when there is some relative velocity across it. But if you're counting on a sta-bar to provide part of your steady-state balance it had better be able to resist load when nothing in the suspension is moving.

I suppose the standard "viewpoint = hard-core cornering performance before ride comfort" disclaimer applies here . . .


02-16-2006, 09:41 AM
I read your post a few times to make sure I was comprehending everything you said. I have a few questions. Please explain your "knee" concept in more detail. I can see a knee in the load deflection curve if the rate of the overall bar changes during deflection. Is that what you mean? Basically, if whatever adjustable spring you were using suddenly changed its rate, you would get a knee. However, if the rate were changed before the deflection, the rate of the bar should stay the same throughout the deflection. What am I missing here?

As for the preload, you're right. Adding preload will not change the spring rate of the bar, but it will change the force the bar is exerting. Maybe that concept could be used for some tuning. The fluid will only work with a relative velocity, but there is always going to be some relative movement. If you combined the fluid with a variable orifice, you could tune the dynamic response and then shut the orifice and depend solely on the rest of the bar for steady state.

Obviously, I haven't designed this or thought it all the way through. My point for bringing it up is that mechanical engineers have to be able to combine mechanical and electronic features in today's world. With the kind of processing that is available these days, we can't afford to limit ourselves to purely mechanical devices. Of course, if you are designing for a pure race car where your environment is much more defined, that is a different story. Most of us mechanical engineers don't get that opportunity.


David Pozzi
02-16-2006, 08:35 PM
I don't have a problem with the discussion going where it may, but blade adjusters work very well and it seems any alternative should be as light and simple to make and use, -unless it provides superior results in some area.

Norm Peterson
02-17-2006, 10:14 AM
I read your post a few times to make sure I was comprehending everything you said. I have a few questions. Please explain your "knee" concept in more detail. I can see a knee in the load deflection curve if the rate of the overall bar changes during deflection. Is that what you mean?Yes. And that will occur with a preloaded spring arrangement as the preload is exceeded by an opposing force that will develop as the bar is loaded.

Basically, if whatever adjustable spring you were using suddenly changed its rate, you would get a knee.In this case, Iím looking at the bigger picture, where the overall rate of the bar would depend on the condition of the preload spring. As long as the adjustment spring is under any preload it will not be contributing any flexibility to the system and the barís rate would be based only on the torsional and bending elements of the bar. Only after the preload is overcome will that spring deflect in accordance with the amount of load it sees, and only then would the barís overall rate include the effects of the adjustment spring (read: youíd then have a softer overall rate).

However, if the rate were changed before the deflection, the rate of the bar should stay the same throughout the deflection. What am I missing here?If you're changing the rate before applying any deflection, you're not adjusting preload. In order to change the overall bar rate over its entire range of deflection, you need to be varying one or more of the individual stiffnesses that comprise the bar, not any of the initial force conditions. Thatís precisely what rotating blade shaped arms or moving the attachment points of endlinks along the arms accomplishes, as should a rather more complicated method for varying the effective torsional resistance of the center section. All start deflecting from their zero stress state at zero point infinitesimal applied bar end displacement.

Adding preload will not change the spring rate of the bar, but it will change the force the bar is exerting. Maybe that concept could be used for some tuning.This can already be done quite simply with conventional bars and existing hardware, i.e. endlinks adjustable for length or shims under the chassis bushings. I suppose that you could use this as part of a cornerweighting procedure in lieu of accomplishing the entire adjustment via the springs.

This is in no way intended as a discouraging comment, but I also think a discussion that includes such things as fluid flow and electronic controls is getting close enough to active suspension and will involve enough additional considerations - some being quite subjective - to justify its own separate thread.


02-17-2006, 02:00 PM
That was a great explanation. I have a different thought in my head, but I have to think about it so I can fully explain what I mean. If I think about it long enough, I may realize that my idea is just plain flawed. :screwy:

Anyway, I will leave the active stuff alone, I think I at least planted a seed for a developing mechanical engineer, which was my intent.


442 Ragtop
03-24-2006, 03:19 PM
How about other mechanical ways of making a sb adjustable?

I can think of a few:

1. An arrangement that lets the arms slide horizontally on the torsion bar. Put them close together, and you effectively have a stiffer arm; move them apart, and its looser.
2. An arrangement that lengthens or shortens the arms. Short arms effectively stiffens the bar.
3. End links with springs in them, with an arrangement to lock out coils of the spring. Lock out all the coils, and you have a stiff bar; lock out just a few and it's looser.

I like 3. the best, since it would work w/ a bar that fits in the stock location.

442 Ragtop
03-24-2006, 03:22 PM
Sorry; Hi, all! I've been lurking so long I didn't even realize I've never posted here. As my alias indicates, I have a 442 convertible, it's a 68, and basically stock right now. W/ plans to upgrade. ;-)

Norm Peterson
03-26-2006, 11:49 AM
How about other mechanical ways of making a sb adjustable?

I can think of a few:

1. An arrangement that lets the arms slide horizontally on the torsion bar. Put them close together, and you effectively have a stiffer arm; move them apart, and its looser.
2. An arrangement that lengthens or shortens the arms. Short arms effectively stiffens the bar.
3. End links with springs in them, with an arrangement to lock out coils of the spring. Lock out all the coils, and you have a stiff bar; lock out just a few and it's looser.

I like 3. the best, since it would work w/ a bar that fits in the stock location.I think years ago there was a commercial offering that used method #3, but I have no idea how well it fared. This approach has a built-in limitation in that you cannot make the bar any stiffer than OE, and even that value is with all of the coils stacked completely solid.

Method #2 is readily do-able, although you might want to be able to move the bar's frame mounts slightly to avoid excessive endlink angularity. Bar stiffness is somewhere between a square and cube function of arm length, so it doesn't take much change in the effective arm length to make a fairly large difference in overall stiffness, and this can easily be made greater than the bar's as-stock-installed value. I know of at least one individual (an engineer & amateur fabricator) who has done precisely this mod for the rear bar on a 4th gen Camaro.


David Pozzi
03-28-2006, 11:31 AM
The method #2 was done a lot with push pull cables on race cars until the blade type came out. Some of the IMSA and Trans-Am cars of the 70's used it. Often they used a slider on a greased anti-roll bar arm.

Adjustable arms with clamps are still in use, the trick is to use long end links which allow more adjustment on the arm without much angularity change. On my vintage Lola, the rear end links are 16" long.

03-29-2006, 09:01 PM
I believe ATS is coming out with just what is being talked about here. I wonder if Shane or Tyler would like to pop in and show off a little. In fact, I'd be interested in one for my '77 Camaro. Hell, I may just do it with a stock car bar.

Uhm... not at this time. The boyz are a little busy with what they have on their plates already.

04-02-2006, 06:40 AM
OK, this is what I want to run on my 71 Chevelle. A anti roll bar from www.wolferacecraft.com . I was told it would be too stiff for the street and cause a understeer problem. This is about the same thing you guys are talking about, except adjustable, right? Could this me made to work on the street? I see them in the jegs catalog, and it says race or street.

Also, seen a pic of a 05 Mustang rear suspension. It uses a panhard bar and a sway bar that is mounted to the LCA w/ links to the frame. I have a stock 4 link in my Chevelle. If I was to make adj. links that go from the sway bar to the frame, how well would that work? (I want it to handle, and hook up 750hp)

Thanks - Ron

04-03-2006, 06:36 AM
The Wolfcraft sway bar is a sway bar in name only. It's designed for dedicated 10.5 drag racing. It's made to keep cars launching straight and lets you adjust preload on the rear tires to maximize traction. It's so stiff that as the car leaves the line and weight is transfered rearward, it is distributed evenly side to side. The result is a rear suspension that in side view functions like a piano hinge. Not the hot ticket for a road car.

Norm Peterson
04-03-2006, 08:49 AM
OK, this is what I want to run on my 71 Chevelle. A anti roll bar from www.wolferacecraft.com (http://www.wolferacecraft.com) . I was told it would be too stiff for the street and cause a understeer problem. The issue for such a huge rear sta-bar is oversteer, not understeer. Those things are marginally streetable in any car; less so in a PT type of car with relatively much better front grip than a skinnies/drag radials strip car. You CAN drive around with it (or any of the similar offerings from other makers), but don't expect much warning when the rear end comes unstuck in a turn taken with any enthusiasm.

As regards the '05 Mustang arrangement, changing the method of attachment of a bar changes its effectiveness, and details other than bar diameter and arm length also matter a great deal.


06-17-2006, 06:01 AM
Hi guys,

Well, as promised I am back with some pics of the designs I did in that ARB assignment using some of the ideas and information which was presented here. I have just been very busy with work and hadn't had the time to post sooner.
The first two pics show the assembly of the ARB Design 1. The Blade is fitted in a T-shaped Joint/Clamp (no bolts shown). There is The Joint itself is fitted to the ARB Tube using splines and locked in place with a bolt groove fixing on splined part of joint. A splined fixture has been chosen to provide the possibility of replacing or using another gauged tube. The blades can be adjusted by loosening the clamp bolts, turning the blades say 90į and then re-tightening the bolts. The ARB is bearing mounted in brackets and the bearing also faces off on the ends of the Joints providing a "frictionless" mounting. This design may work but is rather complex from a design/manufacturing point of view. Also depending on space/application the length of ARB may cause problems.
The alternate joint shown in the third drawing is a simpler design (I think). The Blades are mounted above the Torsion Tube and snug fit in the hole in Joint Block. This time a transverse bolt goes through the slot in the side of the Joint (as shown) and screwed into the Blade root which tightens up against Joint Hole. This locks Blade in either hard or soft position. The joint is bolted to the end of the tube by means of a welded (or even brazed) threaded tube end fixture. Since the Blades are mounted above the Torsion Tube it makes for a more compact design in length.
I haven't added an assembly drawing of second design for obvious reasons but hope to get your imagination going. Well I hope you will be able to see the pics as this is the first time I am trying the attachment feature. Any comments or suggestions would be welcome.

06-17-2006, 08:45 AM
Give Hoerr Racing Products(Peoria, Il.) a call and get a catalog.
They have one that looks like it would be easy to reverse engineer or atleast use cfor a model.
The pics of installed unit and sub-assemblies for anything they offer are very good.

06-17-2006, 08:48 AM
Have you decidedon a material for the blades. What Kind of adjustment range are you hoping to get.

06-17-2006, 09:31 AM
Hey pav,
I saw that adjustable blade kit from HRP the thing that I have noticed with it is that they put the Blade Roots (the round ends) in bearings. I would think that those bearings would introduce some "play" in the whole system and eventually affect the overall handling of the car in "tight" situations. Haven't spoken with anyone who has actually used these bearing mounted Blades but would interest me to know if it is actually how I think it is.

As for the materials. It all depends on the type of application and the length of blades and bars that one uses. Of course it also depends on budget (hehe). For this assignment, I was given certain specs about the length of bar and blades and that is what I had to work with. So depending on the kind of spring rate (just talking about ARB rate here) required the type of material chosen could vary. My specs required me to get a spring rate of 90lb/in to 250lb/in, from a SOFT/SOFT to HARD/HARD position and max. deflection of ARB of 80mm (just over 3 inches). I had to develop a spreadsheet which would give me the max. stresses in the blades and tube. Needed something strong for the given spec. blades so chose a nice 300M HS which was just about suitable working within certain safety limits. A british spec T45 steel was used for the tube. This type of material is used on some Lotus, roll cage, bike frame and aircraft applications. Other possible materials Cr Mo, aircraft spec steel.

06-18-2006, 07:54 AM
If done with a tapered roller bearing(think spindles)there would be little, if any, slop and very free movement. And these would take a hell of a load with zero affect to the whole system.

06-18-2006, 08:08 AM
I am harping in late here as usual, but I have a couple of opinions-

Wow, this is a very interesting project; it is full of challenges and variables.
The idea of the adjustable bar is cool, but one of the main things that I see as a problem is material selection. The designer needs unobtanium which is blessed with ideal properties in stiffness, ultimate strength and weight. It would also need to be ultimately damped to not be part of the spring system adding a variable to the shock damping.
For instance, yield strength (if you use aluminum or even a good alloy) will be an issue if you are running significantly lengths on the arms. This becomes a bigger issue if the bar is in the "soft" position; it will be very easy to get into a condition where you have a force into one wheel that will result in the bar going past critical in yield strength. In a turn, hit a bump and the link is done (bent, but may still work... more adjustment? crash?)

Connection to the LCA and actual motion in the real world environment- Unless the blade is dead on above the LCA, you will have a complex angle of inclination between the sway bar arm and the LCA. IN a typical car, this is dealt with using very heavy arms or good centering or a compromise of both. If you are not well centered, the link will push the bar to one side or the other during compression and tend to be pushed back by the restoring force of the bar. In the case of the adjustable bar, you may find that the mechanics of the adjuster system are significantly stressed at times, perhaps beyond their yield limits.

It may be interesting to look at other shapes as well, especially if you have access to some good FEA rigs. For instance, diamond or oval shaped bar may work out a few of the problems, but introduce some new complexities such as a more limited range of adjustment. If you can do this design in a typical parametric 3D software package like Pro E or SW, you can use one of the FEA suites to really get a good look at the load and stress / yield limits and variables.

I have given no answers here and I hope I have not re-hashed too much. This is a very interesting discussion and I just wanted to throw a couple more variables into the pot. I do a great deal of kinematics and load based design work and I find this sort of discussion very interesting. I hope my comments will be a positive contribution to this thread.

08-02-2006, 01:32 PM
Use the adjustable blades for tuning your bar. One is only need to get results. Math has to be only close, change the angle with a cable adjuster or by hand.

We use this type in GT cars and the driver can make changes for varying track conditions.


Mean 69
08-02-2006, 03:58 PM
Hoerr Racing is another excellent source for blade adjust components. Good folks to work with, lots of knowledge, very courteous.

www.hrpworld.com (http://www.hrpworld.com)


08-03-2006, 11:47 AM
out of curiosity--Why aren't these more popular? Just because they're overkill for the vast majority of cars out there? I guess cost would be a major issue, too.

Awesome ideas, though. Very ingenious.

Norm Peterson
08-03-2006, 05:09 PM
Cost would definitely be an issue, especially if the assembly is held to tolerances close enough to eliminate virtually all "free play". Not much point in having the capability to adjust to within 10 lb/in wheel rate if the amount of "slop" (aka a dead spot around zero bar loading) that gives away the first 50 lbs of force.

It's also another periodic-maintenance item, being in most street-driven cars down there underneath most everything except the water, dust, dirt, slush, etc.

I'd think that it's a rather narrow-focus product, with at best a relatively small portion of the aftermarket sta-bar customer base having a really good grasp of what's going on.

Re: leaving the adjustability to one arm only - I'm not at all convinced that a one-sided adjustment wouldn't introduce a couple of side effects due to the asymmetry (coupling between roll and two wheel bump, and the jacking of some weight around as the car rises and falls in pure 'heave'). Something like that might work for a circle track setup given some extra test'n'tune time, though. Or possibly in a car with very stiff springs and only a small bar for fine-tuning.


10-05-2006, 07:27 AM
Hi everybody I am a frech student in mechanical engineering and I am new on this forum.
Is there anybody who could explain me the following equation in the sheet posted by David Pozzi on the first page:

dv= 1.2 Pl / G b (H-h) * ln(H/h)

Thank you very much and excuse me for my poor english...

Norm Peterson
10-05-2006, 08:33 AM
[Force P] * [Length l] / {[Shear Modulus G] * [Section Width b] * [Section Height H,h function]} looks like an equation for estimating shear deflection in arms of non-uniform depth.

Generally this is only a minor effect with the possible exception being in very specific situations where the arms are deep (large H & h) and short (small l ) and the central torsional section is short.

Most of the time, center-section torsion and arm bending account for at least 95% of the total bar deformation (making them primarily responsible for its overall rate).


04-14-2009, 08:10 AM
i know this is an old conversation, but what about a linear actuator instead of the sway bar arms. Obviously the actuator would need to be strong enough to support the loads. Just simple beam theory. Then you have your adjustment in a neat package with all the cool factor.

Norm Peterson
04-18-2009, 06:53 AM
Are we talking about active or partially active suspension, with an actuator at each corner?

I would think that a linear actuator would have a relatively fixed stiffness but a wide range of possible positions. Assuming that you have some way of controlling the positions of the LA's, you'd attach them directly to the chassis and make them responsible for limiting roll. You wouldn't then need any part of a sta-bar at that end.


04-22-2009, 11:54 AM
Actually what i was thinking was to use a linear actuator for the sway bar arm (connection between the end link and the torsion bar) this would be able to vary the length of the arm and therefore vary the spring rate of the torsion bar.


k is the spring constant of the bar

P is the force applied and this will be proportional to the body roll

deg is the rotaion and again proportional to the body roll

M is the length of the arm (moment arm) this is what would be driver adjusts from the cockpit. the linear actuator.

Norm Peterson
04-23-2009, 04:56 AM
I guess that would be do-able, if somewhat heavier and bulkier. Keep in mind that every additional piece in the load path along the bar that isn't firmly attached to some other piece is a potential location for lost motion, more so if wear develops between separate arm pieces courtesy of shear and bending loads. I would hope that placing threads in bending isn't being considered.


04-23-2009, 05:33 AM
didnt know about this thread, havent read the whole thing but im in the middle of designing one for our fsae car currently

leafs are going to be Ti (stuff we had laying around so dont know what kind) and 4130 for cups and tubes.

we made a test piece and used weights and dial indicators to test if simple tubes in torsion and beams in bending calculations will be applicable or not.... turns out not really..
especially the leaf is hard to model/design with pure static equations.
(lots of assumptions had to be made)

so if you really want to get a blade style arb setup to work the way you want it, i recommend making 1, testing, redesign, repeat.

btw, watch those stress calculations too.

David Pozzi
04-26-2009, 10:24 PM
Ralt pioneered the use of blade adjusters with constrained ends to prevent side to side deflection of the end links. He built guides to restrict any side to side movement.

In your testing, have you seen this happen?

05-06-2009, 12:00 AM
I tried to read most of your posts so I understood the conversation. You guys can really go off.

My situation is I need sway bars on my car and since I dont want to spend a grand on kits I need to make them. Can I use chromoly to make a predictable swaybar? I was thinking around 1" x .085. 4130 is common chromoly right? I know moly has spring to it but will it spring back to its original position when used as a sway bar?

My guess is the bar will be just over 30" and twist 1/8" with full articulation. I want to use tubing for weight and moly for availability.

Next topic. This is the first time I've heard of blades for the arms. In my case these would be nice considering my rear bar will most likely be inside the car with small holes for the connector links. Now what type of steel would the links be made of? Also as you rotate the blades wont they gain a certain amount of sideways deflection?

I just realized Im only on page one of the posts. I hope these questions werent already answered.

Norm Peterson
05-06-2009, 03:29 AM
OE Tubular bars are typically made from tubing where the wall thickness is about 15% of the OD.


05-06-2009, 11:23 PM
So, if I chose a 1" tube it would need to be .150 thick. The thing is I'm not talking about OE bars. I want to buy steel from my local dealer that will work. Do you know if moly will hold up?

In my mind 1"x0.125 seems like it would take the stress. I havent checked what is available or available for a reasonble price yet.

Basically what I want to know is my options on tube that I can buy to use for a sway bar.

Norm Peterson
05-07-2009, 02:57 AM
I figure that the OE's have settled on 15% with the benefit of much more detailed analytical methods and a lot more actual experience. That said, 1/8" has a much better chance than 14-gauge.

Don't overlook bending loads, shear, combined stress, and buckling. The central portion is generally NOT loaded in pure torsion.

Have you checked out the circle track supply houses? I know you can get tubular torsion sections in a variety of stiffness and the arms separately.