Sway Bar Adjustment

[2BWise]

Instead of talking about it you could do an experiment and measure it.

-Put the car on scales.
-Adjust one ARB linkage to be significantly different in length on one side of the bar.
-Then take some blocks (roughly 1/8" to 1/4") and slide them under one of the wheels. Record the corner weight measurements (record all 4 corners).
-Remove the blocks and then put them under the other side. Record the corner weight measurements.

If the recorded values are the same (or within measurement error) then the bar rate is independent of the ARB linkage length. If it changes relative to the side with the long/short ARB linkage then you'll know the rate is dependent of the ARB linkage length.

****I realized I didn't complete the process here. With a little math its possible to get an interesting piece of data, once you have the wheel displacement and the corner weights.
*-take the weight difference across each axle and multiply it by the track width (you'll end up with a torque)
*-add up that torque for the front axle and rear axle (the total front to rear moment difference)
*-using the height the wheel has been displaced calculate the total angular displacement (height divided by track width)
*-take the total torque divide by the angular displacement and you end up with the total torsional stiffness of the system.

If you modify springs, bars, tires, etc (anything that has a steady state effect on the handling balance) you can compare the magnitudes of those changes by doing the above comparison.

[killerken53]

Instead of talking about it you could do an experiment and measure it.

-Put the car on scales.
-Adjust one ARB linkage to be significantly different in length on one side of the bar.
-Then take some blocks (roughly 1/8" to 1/4") and slide them under one of the wheels. Record the corner weight measurements (record all 4 corners).
-Remove the blocks and then put them under the other side. Record the corner weight measurements.

If the recorded values are the same (or within measurement error) then the bar rate is independent of the ARB linkage length. If it changes relative to the side with the long/short ARB linkage then you'll know the rate is dependent of the ARB linkage length.

One test is worth 1000 expert opinions...

[john f]

Instead of talking about it you could do an experiment and measure it.

-Put the car on scales.
-Adjust one ARB linkage to be significantly different in length on one side of the bar.
-Then take some blocks (roughly 1/8" to 1/4") and slide them under one of the wheels. Record the corner weight measurements (record all 4 corners).
-Remove the blocks and then put them under the other side. Record the corner weight measurements.

If the recorded values are the same (or within measurement error) then the bar rate is independent of the ARB linkage length. If it changes relative to the side with the long/short ARB linkage then you'll know the rate is dependent of the ARB linkage length.

I agree with your idea, but with some questions:

1) I don't think 1/8"-1/4" under one wheel is a realistic amount of movement for the driver to feel anything. You get those kinds of motion on a straight. Yes, you will see a slight weight change, but should the motion be greater, say 1/2-1 1/2"?
2) what is a reasonable error? 1#, 5#, 20# ? How accurate and what is the resolution/repeatability of the scale.

Not poo-pooing the idea, I like it, but if done, details matter, I think.

john f

[DaveW]

Instead of talking about it you could do an experiment and measure it.

-Put the car on scales.
-Adjust one ARB linkage to be significantly different in length on one side of the bar.
-Then take some blocks (roughly 1/8" to 1/4") and slide them under one of the wheels. Record the corner weight measurements (record all 4 corners).
-Remove the blocks and then put them under the other side. Record the corner weight measurements.

If the recorded values are the same (or within measurement error) then the bar rate is independent of the ARB linkage length. If it changes relative to the side with the long/short ARB linkage then you'll know the rate is dependent of the ARB linkage length.

I hope you meant ARB arm (moving the link closer to or further from the pivot), not ARB link. And you should move it a significant % of the arm length to get an effect greater than measurement errors. We all know that lengthening or shortening a link (preloading) will change the corner weights.

You also, IMO, have to make sure you adjust the link lengths (no swaybar preload) after you move the link with the shims not in place so you're not just seeing the jacking effect that moving an angled link would provide. Then put the shim in and see what it does. Then move the shim to the other side to see if the change is different side-side.

[2BWise]

I agree with your idea, but with some questions:

1) I don't think 1/8"-1/4" under one wheel is a realistic amount of movement for the driver to feel anything. You get those kinds of motion on a straight. Yes, you will see a slight weight change, but should the motion be greater, say 1/2-1 1/2"?
2) what is a reasonable error? 1#, 5#, 20# ? How accurate and what is the resolution/repeatability of the scale.

Not poo-pooing the idea, I like it, but if done, details matter, I think.

john f

The more input to the wheel the better. Small travels will show higher stiffnesses than what are truly occurring due to friction and hysteresis in suspension. My preference would be to make 1/8" step increases up to about 1.5" if you can get there without a wheel coming off of the pads. The further the height the more accurate the result, but tracking the measurements at each step. Measurement error will be up to the repeatability of the scales you are using. A swag; anything outside of 5% would probably indicate a realistic stiffness delta. Running the test multiple times would be the best way so that you could do a statistical analysis of the results and the signal-noise ratio.

I hope you meant ARB arm (moving the link closer or farther from the pivot), not ARB link. We all know that lengthening or shortening a link (preloading) will change the corner weights.

You also, IMO, have to make sure you adjust the corner weights after you move the link with the shims not in place so you're not just seeing the jacking effect that moving an angled link would provide. Then put the shim in and see what it does. Then repeat the same sequence on the other side to see if the change is different side-side..

Yes of course.

And agreed. Before each test the car needs to be corner weighted such that the starting values are close to the same and that there is no initial preload in the ARB.

[TimH]

You also, IMO, have to make sure you adjust the link lengths (no swaybar preload) after you move the link with the shims not in place so you're not just seeing the jacking effect that moving an angled link would provide. Then put the shim in and see what it does. Then move the shim to the other side to see if the change is different side-side.

Actually, NOT adjusting the link lengths would better duplicate the effect of a one-sided cockpit adjuster.

[DaveW]

Actually, NOT adjusting the link lengths would better duplicate the effect of a one-sided cockpit adjuster.

You're correct, but I was trying to define a more "pure" test of the effects of arm length and nothing else.

[alangbaker]

Getting back to the original question:

I'm going to intersperse some comments, and I'll try and remove the material I'm not addressing.

There have been points made on here about the bar not being 'fixed' but surely this isn't correct. Think of a very thin ARB. This will twist given a very small moment at one end, such that the other end will deflect little or nothing. What it won't do is transfer the whole angular movement and applied moment to the opposite side. Thus it is - essentially - 'fixed' to a given extent based on its stiffness (or lack of).

Except for the friction in the mounts, all the applied moment at one end must be matched by an equal but opposite moment applied to the other end.

Now since all ARB's deflect (unless so massively thick they are simply a solid link) this will always be the case. In the following I have assumed the ARB is not that stiff so there is some rotational deflection within it when a moment is applied.

You were correct the first time: ALL ARBs deflect.

So (working with the two linkages of the same length), given a fixed upward force 'f' through the linkage at one end of the bar, applied at a distance 'l' from the rotation axis, the resultant moment will be 'f x l'. A quantity of that moment will cause twisting in the bar and the remainder will be applied as a moment to the opposite-end linkage. By dividing the latter moment by the length of that side's arm 'l' the resultant upward force transmitted to the wheel will be calculated.

No "quantity of that moment" is lost in the twisting of the bar. That's exactly like saying that if you have a coil spring on a scale and put a 10 pound weight on it, the scale will read something less than 10 pounds.

If we shorten the linkage to, say, 'l/2' on one side only so the two are unequal lengths and apply the same force 'f', then the moment becomes ' f x l/2', so half the original value. When applied, twist in the bar will require the same moment as in the first example, so the remainder that is transferred to the opposite wheel will be smaller. The resultant force applied to the opposite wheel can be calculated in the same way as above by dividing by 'l' and will - as the moment is lower - be smaller also.Now, if we keep the same setup as above, ie. with unequal-length linkages, and apply the force 'f' at the opposite end we will get a moment 'f x l'. Again, a fixed amount of that moment will cause twist in the bar and the rest will be transferred to the other end. The resultant force can be calculated by dividing the moment by the linkage length (ie. 'l/2') so the force on the wheel will be higher.

Once you remove the stuff about "remainders", this is essentially correct. If you make the bar ends unequal in length, the forces on they apply to the links and thus to the uprights MUST be unequal in precise proportion.

Edit: Please challenge this as, having written it with such initial certainty, I am reading it through and wondering...

Edit 2: ...and, having thought, all the above is possibly more relevant to when one wheel is in 'bump', ie. an instantaneous force is applied to one end of the ARB setup, so the bar is, effectively, working as an additional spring rather than to control roll.

The ARB acts as an additional spring any time there is unequal vertical movement of the pair of wheels it connects.

In the latter case the applied moment is around the roll axis of the car and the 'lever' length is the distance between the CG and the roll centre for whichever end of the car (front or rear) that's under scrutiny. So there is a simultaneous upward moment applied to one end of the ARB and a downward moment to the other. Can we assume these are equal?

Some of this moment will be taken up by twist in the ARB and the remainder will be applied via the end linkages as a force onto to the wheels. If the linkages are the same length then the force on the wheels will be equal and in opposite directions.

If the linkages are not equal then the applied forces won't be either. My gut feeling is that the 'softer' end (ie. the one with the longer linkage) will either droop or jack further depending on whether the roll is towards or away from it.

[tlracer]

To address the point that I raised and which both John f and alangbaker have responded:

Applying a moment at one end of the ARB twists it (ie. it acts like a torsion bar). As I said towards the start of my post, take the extreme example of a very thin ARB, on bump this will twist easily so the displacement is not immediately transferred to the other end.

Essentially this is putting energy into the bar as it twists; that energy is released either as displacement at the opposite end or in returning the 'input' end to its original state.

On consideration (Edit 2) my initial thoughts applied primarily to instantaneous 'bump' rather than 'roll' (= cornering). As I recall, wasn't this exactly why the monoshock/Belleville washers setup was introduced? To separate bump and roll in the anti-roll mechanism.

So to clarify, I'm not suggesting anything 'disappears', rather that it is 'delayed' in transfer.

Certainly I agree this is something that warrants further investigation. As well as the experimentation already suggested, another would be to set varying differences in ARB arm lengths and look at the effect on ride height, etc. when true 'roll' is applied to the chassis.

[john f]

To address the point that I raised and which both John f and alangbaker have responded:

Applying a moment at one end of the ARB twists it (ie. it acts like a torsion bar). As I said towards the start of my post, take the extreme example of a very thin ARB, on bump this will twist easily so the displacement is not immediately transferred to the other end.

Essentially this is putting energy into the bar as it twists; that energy is released either as displacement at the opposite end or in returning the 'input' end to its original state.

On consideration (Edit 2) my initial thoughts applied primarily to instantaneous 'bump' rather than 'roll' (= cornering). As I recall, wasn't this exactly why the monoshock/Belleville washers setup was introduced? To separate bump and roll in the anti-roll mechanism.

So to clarify, I'm not suggesting anything 'disappears', rather that it is 'delayed' in transfer.

Certainly I agree this is something that warrants further investigation. As well as the experimentation already suggested, another would be to set varying differences in ARB arm lengths and look at the effect on ride height, etc. when true 'roll' is applied to the chassis.

Concerning the first part re thin ARB. Physics is physics. Torque in = torque out. To put something in, no matter how small, you need something else to resist is.

john f

[Daryl DeArman]

I'm back
I do not want to cause trouble, but I have a problem with the above description. If the torque input does not transfer to the other end of the bar, where did it go? The bar itself does not "use up" some of the torque. That would be saying that when you use a torque wrench with an extension, you are not getting the full torque to the fastener you are tightening. The torque that you input in the driveshaft is not all delivered to the pinion? The torque you input to the steering wheel doesn't all make it's way to the steering box?

If you do what is called a "free body diagram" of the sway bar, there are a total of 4 forces being input into the bar. The 2 links at the ends and your 2 mounting points. Nothing else. Neglecting the weight of the bar, when the car is level, with no preload, these four points are carrying the weight of the bar. At this point there is no bending moment induced in the bar. The moment we move one link up or down, the loading on the other points change. The free body analysis shows the direction and magnitude of each of the mounting points. It will also show that we are now generating a bending moment in the bar.

If one link is moved up, by a given force, either the other link has to resist the force an equal amount (equal length arms) or that end will just move up. no resistance, no moment. Put your torque wrench on a loose nut and turn the wrench. no resistance from the nut, no torque.

Now, there is one caveat in the previous description. The mounting points of the bar on the chassis. As the mounts are a rotating bearing as such, this point can generate friction, which will require a torque to overcome. It is at these 2 points where a percentage of torque can be lost. If this amount is more than a few percent, you have got a bound up bar.As problemchild stated in post #45:

" but IMO, an external traditional ARB with very good bearing mounts, as used on most VFFs and CFFs may be the best performing ARB option. A bigger ID hollow ARB is best, and reducing the stiction in the bearing mounts is most important."

My description assumes good bearing mounts.

Please note that I am not trying to "one up", "bash", taut my education, or years of experience. The biggest thing I learned in school eons ago was "I learned how to learn". I am always open to learning, but I prefer it be correct info . That's my $0.02.

john f (john f boxhorn)

Nothing to disagree with there, unless I just want to be disagreeable and state that there is some torque being applied on that loose nut, just maybe not enough for you to feel or the wrench to indicate. Not unlike almost "stiction free" bearing mounts and clevis joints

[Daryl DeArman]

Instead of talking about it you could do an experiment and measure it.

-Put the car on scales.
-Adjust one ARB linkage to be significantly different in length on one side of the bar.
-Then take some blocks (roughly 1/8" to 1/4") and slide them under one of the wheels. Record the corner weight measurements (record all 4 corners).
-Remove the blocks and then put them under the other side. Record the corner weight measurements.

If the recorded values are the same (or within measurement error) then the bar rate is independent of the ARB linkage length. If it changes relative to the side with the long/short ARB linkage then you'll know the rate is dependent of the ARB linkage length.

Depending on wheel rate and corner weight of the car you could have a significant change on the scales even without an ARB. Roll center height, cg height etc. You are moving crap around those points, weight is going to go somewhere. Junk in ----> Junk out.

[tlracer]

Concerning the first part re thin ARB. Physics is physics. Torque in = torque out. To put something in, no matter how small, you need something else to resist is.

john f

This rather takes one part of my post out of the total context.

Displacement in does not equal displacement out instantaneously. The bar twists, storing energy that is subsequently released as I went on to describe

[billtebbutt]

I have no personal experience with a stiffer front bar reducing U-S. As you mentioned, in most circumstances, a stiffer front bar should increase U-S by increasing front weight transfer while decreasing it at the rear.

However, in the case of heavily rising rate front suspension, as I mentioned in the FV post, one can help minimize the wheel rate increase during cornering (which creates U-S) by minimizing roll. Positive camber during cornering could also be reduced by reducing the roll angle as in the FV if the camber gain is low.

So, IMO, while the effect of a front bar stiffness increase is usually more U-S or less O-S, in special circumstances the opposite can occur.

An effect I have experienced is that the front roll stiffness has more effect on the car's response rate than its U-S/O-S balance. The rear bar always has seemed to have a much greater effect on balance.

On my RF82, I was using the stock bars (puny!) front and rear. Could not stop the understeer. My pal David Clubine wondered if it wasn't rolling so far that we weren't reducing the contact patch, causing the issue... Called Simon at Universal and told him what I was using for bars; my, he laughed at the colonist (was already using the recommended springs). bolted on a HUGE front bar + slightly larger rear bar. Problem solved, but it still hurts to think about it!!!!

BT

[alangbaker]

To address the point that I raised and which both John f and alangbaker have responded:

Applying a moment at one end of the ARB twists it (ie. it acts like a torsion bar). As I said towards the start of my post, take the extreme example of a very thin ARB, on bump this will twist easily so the displacement is not immediately transferred to the other end.

Essentially this is putting energy into the bar as it twists; that energy is released either as displacement at the opposite end or in returning the 'input' end to its original state.

This rather takes one part of my post out of the total context.

Displacement in does not equal displacement out instantaneously. The bar twists, storing energy that is subsequently released as I went on to describe

I'm sorry, but there is in no practical sense of the word any delay at all. The speed of sound in steel is 5,960 metres per second. So the time for a force at one end of a bar with the hugely over-estimated length of 2 metres would be something around 3 ten thousands of a second.

The moment a force is applied to one end of the ARB, the other end immediately applies a force to the link attached to it.

[2BWise]

Depending on wheel rate and corner weight of the car you could have a significant change on the scales even without an ARB. Roll center height, cg height etc. You are moving crap around those points, weight is going to go somewhere. Junk in ----> Junk out.

That is entirely the point. By displacing the wheel some amount the vehicle responds by transferring weight. The amount of weight transferred is proportional to torsional resistance of the entire vehicle.......roll resistance! It is a collection of springs. If you modify the stiffness of the ARB you will see the change in weight distributed across the front and rear. Just don't change more than one variable at a time.

[Daryl DeArman]

That is entirely the point. By displacing the wheel some amount the vehicle responds by transferring weight. The amount of weight transferred is proportional to torsional resistance of the entire vehicle.......roll resistance! It is a collection of springs. If you modify the stiffness of the ARB you will see the change in weight distributed across the front and rear. Just don't change more than one variable at a time.

Agreed.

I read the proposed "test" to imply that seeing weight transferred in an inconsistent manner left vs. right with bar legs set to different stiffnesses proved the hypothesis. When in fact, all it proves is the entire assembly does not transfer weight for a given amount of wheel travel or roll equally left to right. The variables are numerous, not limited to actual wheel rates, torsional rigidity of chassis, how roll centers move L vs. R, CG location not being centered left/right, etc.

[tlracer]

I'm sorry, but there is in no practical sense of the word any delay at all. The speed of sound in steel is 5,960 metres per second. So the time for a force at one end of a bar with the hugely over-estimated length of 2 metres would be something around 3 ten thousands of a second.

The moment a force is applied to one end of the ARB, the other end immediately applies a force to the link attached to it.

The ARB is nothing more than a torsion spring with a lever at either end. Energy input, through displacement at one end (or, indeed, both), is partly stored by the bar twisting. Only once the conditions change will that stored energy be returned to the system.

That is the sole purpose of it, to limit energy transfer across the car and, thus reduce the degree of rotation of the sprung part of the vehicle, ie. chassis, engine, driver, etc.

The point in question is whether, with uneven length levers, the behaviour of the car will differ side-to-side.

[DaveW]

The best thing about this thread is that now everyone that has read it will be aware of what "can" happen with unequal lever arms on the swaybar. More knowledge never is a bad thing, IMO.

[problemchild]

The worst thing about this thread is that now everyone that has read it still does not understand that nothing bad will happen with unequal lever arms on the ARB. Too much "wickipedia" knowledge and tortured math can be a bad thing, IMO.

[DaveW]

The worst thing about this thread is that now everyone that has read it still does not understand that nothing bad will happen with unequal lever arms on the ARB. Too much "wickipedia" knowledge and tortured math can be a bad thing, IMO.

You're certainly right. The proof is how does it really work. And I'm sure that because it worked for you and many others in the past, it'll work equally well for others. But you also understand the possible pitfalls, and now more racers do...

[BorkRacing]

The ARB is nothing more than a torsion spring with a lever at either end. Energy input, through displacement at one end (or, indeed, both), is partly stored by the bar twisting. Only once the conditions change will that stored energy be returned to the system.

That is the sole purpose of it, to limit energy transfer across the car and, thus reduce the degree of rotation of the sprung part of the vehicle, ie. chassis, engine, driver, etc.

The point in question is whether, with uneven length levers, the behaviour of the car will differ side-to-side.

Actually an ARB is a series of 3 springs.
We know from the basic formula for springs in series that the rate of any ARB, K, can be found by the following equation:

1/Ktotal= (1/Ktorsion+1/Kbending+1/Kbending) to the -1 power (sorry can't write proper equations on my phone

We use 2x Kbending because there are 2 arms. If you notice the equation does not care what the arm length is, only its ultimate value.
So an ARB with different length arms can be rated the same as one with equal arms. Physics does not care how long the arms are in relation to each other, it wants the final values

The important fact to grasp here is an ARB is a complete system of 3 springs in series, not isolated left and right systems.
An ARB with arms 10 and 20 inches long will have the rate as one with both arms 15 inches long.

Now we need to look at how the ARB works. First an ARB does not produce force on its own out side of a system. Just like a spring does not move unless you apply a force to it, neither does an ARB. A perfect exampe is go look at your car sitting in your shop. I have 4 in mine right now and another 4 bars I just made for a customer. They are all just sitting quietly.

What type of system do we place an ARB in for our type of car? We put it in a system that when later force (G force) is applied the car rolls. I have done lots of chassis analyses and in this example we will use a 30 Series Crossle rear suspension. I can set the car up so that the roll center is at ground plane with no lateral or vertical migration. I can also set it up so that the car rolls 1* when the suspension move 1 inch on either side of the car. Also for this example we will mount the bar such that the links are always at 90* to the arm.

So roll the car 0.5*. What happens? One side goes down 0.5 inches and the other rises 0.5 inch. (Note: for simplicity this makes the bar move a total of 1" as most are rated in lbs/inch)What happens to an ARB with equal lengths? It follows the suspension change and torques. One spring compresses and one spring expands on the suspension as well. The Cosmos being what it is and the current rules of physics we live under likes to see equilibrium. So the compressed spring wants to expand and the torqued ARB wants to return to its resting state. Where are these forces being applied to our system to get back to equilibrium?

Physics being physics the ARB (as a series of springs) does not know where the resisting forces are coming from, arm 1, arm 2 or the main bar. It is a total system and will deliver them equally throughout the system.

The spring is easy, it is trying to raise the lower side back to ride height and be in equilibrium with the opposite spring and to bring the ARB back to its neutral state. The ARB is doing the same. It is trying to untwist its self or resist the forces placed on it (this is an important concept) by the roll of the suspension. Which side of the car the spring applies force to is easy, the side where the spring is compressed. Which side(s) does the ARB apply force to as it tries to return to its neutral state? Well, everyone here agrees it applies it equally to both side of the car and that is a correct assumption, but why does it apply it equally? Because the arms are the same or because the ARB is a series of springs acting together? Remember the equation for springs in series? It does not care what the arm length are for its total rate. So in a closed system like the Crossle' rear suspension, the ARB acts across both sides equally because it is a series of springs, not because of equal arm length.

What happens in this example if we now make the arm lengths uneven. Well we get a new rate, Ktotal, for our bar. Everything moves and rolls the same and forces are applied the same because the bar is connected to both sides and activated by the action of the car rolling. The bar will not and cannot act as 2 separate systems and react with different forces on different sides because the suspension in roll is not 2 separate systems. Put the suspension in 0.5* roll and it acts on the total ARB, not its individual parts. It may seem to be acting on individual parts but the rate equation tells us the force is considered as a whole and the suspension is reacting to the bar as a whole.

If you want a check for this, then create an ARB with equal arms but with 2 different diameters in the main bar, say the left half is 1/2 inch and the right half is 1 inch. Do you expect different rates on different sides now or will the bar act again as a series of springs? Will there be more force on one side versus the other or will they be equally divided from the total bar rate, Ktotal?

Please consider that this is just one of many instances of how our suspension works and anyone of you can dream up positions for the uprights, springs, shocks, Roll center and ARB where the force could vary.

Final thoughts? Remember a spring or an ARB only pushes back when it gets pushed. Much like me!

[problemchild]

You're certainly right. The proof is how does it really work. And I'm sure if it worked for you, it'll work for others. But you also understand the possible pitfalls, and now more racers do...

I see no possible pitfalls. I see a bunch of people who will get intimidated by a bunch of engineering mumble jumble, and rather than apply common sense and logic, will just believe what "smarter" people are telling them. We don't need Wikipedia pages with "static" formulas, or simulated tests. Daryl's fat kids on the teetor totter analogy says it all.

Threads like this become engineering debates, arguing about percentage points of theoretical differences, and don't help the common racer.

The common racer only needs to know that he needs to be careful with the link preload if his ARB linkage is not symmetrical.

[stonebridge20]

Lee Stohr chuckled his way through this whole thread.

[alangbaker]

The ARB is nothing more than a torsion spring with a lever at either end. Energy input, through displacement at one end (or, indeed, both), is partly stored by the bar twisting. Only once the conditions change will that stored energy be returned to the system.

That is the sole purpose of it, to limit energy transfer across the car and, thus reduce the degree of rotation of the sprung part of the vehicle, ie. chassis, engine, driver, etc.

The point in question is whether, with uneven length levers, the behaviour of the car will differ side-to-side.

I'm sorry, but the idea that there is some "delay" in the torque and ultimately the force getting transmitted to the other end is just so much nonsense. As has been pointed out to you, there can be no force at one end unless there is a force at the other end opposing it.

In short, if the ARB is to have any impact on the loading of one side, it MUST also be impacting the loading of the other side ( for the sake of completeness, I mention the only exception is the case at the limit where the link is fastened to the bar at zero distance from the axis).

Hence if the links are fastened unevenly, and the longer link L1 is being pushed up so that the bar is pushing back with x pounds of force, then the shorter link L2 will be pulling up on its link with y pounds of force where y = x * L1/L2. If you now corner in the opposite direction, so that you get x pounds of force on the L2 link, you will get y' = x * L2/L1.

That is going to produce an asymmetric effect on the suspension, and the effect will be the square of the ratio of the arm lengths.

Just imagine a car with hypothetical suspension where there is a spring that only resists double wheel motion and only the ARB resists in roll.

When you corner so that the longer bar is on the outside, the car will lose ride height; changing the suspension geometry to one that (usually) has less geometric resistance to roll as compared to when you corner the other way with the shorter bar on the outside when the car will gain ride height and thus (usually) geometric roll resistance.

Whether the asymmetry would be large enough to be a problem in practice... ...I can't begin to tell you.

[DaveW]

I'm sorry, but the idea that there is some "delay" in the torque and ultimately the force getting transmitted to the other end is just so much nonsense. As has been pointed out to you, there can be no force at one end unless there is a force at the other end opposing it.

In short, if the ARB is to have any impact on the loading of one side, it MUST also be impacting the loading of the other side ( for the sake of completeness, I mention the only exception is the case at the limit where the link is fastened to the bar at zero distance from the axis).

Hence if the links are fastened unevenly, and the longer link L1 is being pushed up so that the bar is pushing back with x pounds of force, then the shorter link L2 will be pulling up on its link with y pounds of force where y = x * L1/L2. If you now corner in the opposite direction, so that you get x pounds of force on the L2 link, you will get y' = x * L2/L1.

That is going to produce an asymmetric effect on the suspension, and the effect will be the square of the ratio of the arm lengths.

Just imagine a car with hypothetical suspension where there is a spring that only resists double wheel motion and only the ARB resists in roll.

When you corner so that the longer bar is on the outside, the car will lose ride height; changing the suspension geometry to one that (usually) has less geometric resistance to roll as compared to when you corner the other way with the shorter bar on the outside when the car will gain ride height and thus (usually) geometric roll resistance.

Whether the asymmetry would be large enough to be a problem in practice... ...I can't begin to tell you.

I think you are arguing about semantics - while the bar is twisted, of course it stores some energy, which it gives back when the bar goes back to its unloaded position.. However, the force effects on the car's handling are pretty much instantaneous.

[DaveW]

I see no possible pitfalls. I see a bunch of people who will get intimidated by a bunch of engineering mumble jumble, and rather than apply common sense and logic, will just believe what "smarter" people are telling them. We don't need Wikipedia pages with "static" formulas, or simulated tests. Daryl's fat kids on the teetor totter analogy says it all.

Threads like this become engineering debates, arguing about percentage points of theoretical differences, and don't help the common racer.

The common racer only needs to know that he needs to be careful with the link preload if his ARB linkage is not symmetrical.

And to just be aware that if he has an issue of unequal response in LH v RH turns, it "could" be a result of a large difference in LH to RH lever length. Otherwise I don't disagree with what you said.

[billtebbutt]

I see no possible pitfalls. I see a bunch of people who will get intimidated by a bunch of engineering mumble jumble, and rather than apply common sense and logic, will just believe what "smarter" people are telling them. We don't need Wikipedia pages with "static" formulas, or simulated tests. Daryl's fat kids on the teetor totter analogy says it all.

Threads like this become engineering debates, arguing about percentage points of theoretical differences, and don't help the common racer.

The common racer only needs to know that he needs to be careful with the link preload if his ARB linkage is not symmetrical.

Can't say "fat kids". Nor does any municipality in Canada, that I can tell, equip parks with teeter totters anymore. So I am unable to understand Daryl's analogy.

But, we do have legal weed.

(Will show myself out now)
bt

[Daryl DeArman]

Lee Stohr chuckled his way through this whole thread.

Ignorant of the Stohr suspension designs. I'm assuming he's found success without utilizing ARB's at all.

[tlracer]

I'm sorry, but the idea that there is some "delay" in the torque and ultimately the force getting transmitted to the other end is just so much nonsense. As has been pointed out to you, there can be no force at one end unless there is a force at the other end opposing it.

In short, if the ARB is to have any impact on the loading of one side, it MUST also be impacting the loading of the other side ( for the sake of completeness, I mention the only exception is the case at the limit where the link is fastened to the bar at zero distance from the axis).

Hence if the links are fastened unevenly, and the longer link L1 is being pushed up so that the bar is pushing back with x pounds of force, then the shorter link L2 will be pulling up on its link with y pounds of force where y = x * L1/L2. If you now corner in the opposite direction, so that you get x pounds of force on the L2 link, you will get y' = x * L2/L1.

That is going to produce an asymmetric effect on the suspension, and the effect will be the square of the ratio of the arm lengths.

Just imagine a car with hypothetical suspension where there is a spring that only resists double wheel motion and only the ARB resists in roll.

When you corner so that the longer bar is on the outside, the car will lose ride height; changing the suspension geometry to one that (usually) has less geometric resistance to roll as compared to when you corner the other way with the shorter bar on the outside when the car will gain ride height and thus (usually) geometric roll resistance.

Whether the asymmetry would be large enough to be a problem in practice... ...I can't begin to tell you.

I don't disagree; indeed I am quite certain that unequal ARB lever settings will result in handling differences side-to-side.

With hindsight, perhaps the word 'delay' was not the best; substitute 'modulate', such that the energy stored, as the input force twists the bar, means there is not 100% transfer to the other end.

Hope this clarifies.

[alangbaker]

I don't disagree; indeed I am quite certain that unequal ARB lever settings will result in handling differences side-to-side.

With hindsight, perhaps the word 'delay' was not the best; substitute 'modulate', such that the energy stored, as the input force twists the bar, means there is not 100% transfer to the other end.

Hope this clarifies.

It does clarify your thinking...

...but your thinking remains incorrect.

There is absolutely 100% transfer of the torque to the other end of an ARB.

Your position is no different than claiming that because energy will be stored when you compress a coil spring, that less than 100% of the force used to compress it will be transferred to the other end. I invite you to place a coil spring onto a scale, zero it, then put a 10lb weight on top of the spring.

The force/torque at one end of a spring must be matched by exactly an equal but opposite force/torque at the other end.

[tlracer]

Certainly, if you do that and leave the weight there the system you describe will reach equilibrium, I don't disagree.

In that experiment the spring will, as I have explained, store energy. This will be equivalent to the change in potential energy due to the change in height of the mass as the spring compresses.

Only when the mass is removed will that energy be released by the spring.

The nearest vehicle dynamic I can think of to your analogy is cornering; the ARB twists, storing energy, which is only released as the corner is exited and straight line motion is resumed.

There is another situation where the ARB will store energy, but for a much shorter time - instantaneous bump force through one wheel. In this case it is like putting s spring on a balance and hitting it. The energy imparted to the spring will compress it, releasing only with the natural frequency of the spring. But will the scale register the instantaneous force in full?

I sense, however, that this is all getting somewhat academic, given that we are agreed that different length arms on the ARB isn a good idea!

[stonebridge20]

Ignorant of the Stohr suspension designs. I'm assuming he's found success without utilizing ARB's at all.

Yep !

[alangbaker]

Certainly, if you do that and leave the weight there the system you describe will reach equilibrium, I don't disagree.

In that experiment the spring will, as I have explained, store energy. This will be equivalent to the change in potential energy due to the change in height of the mass as the spring compresses.

Only when the mass is removed will that energy be released by the spring.

The nearest vehicle dynamic I can think of to your analogy is cornering; the ARB twists, storing energy, which is only released as the corner is exited and straight line motion is resumed.

There is another situation where the ARB will store energy, but for a much shorter time - instantaneous bump force through one wheel. In this case it is like putting s spring on a balance and hitting it. The energy imparted to the spring will compress it, releasing only with the natural frequency of the spring. But will the scale register the instantaneous force in full?

Tim, let me try one more time.

It is impossible for the spring to store any energy unless there is a force acting on it on BOTH ENDS. An ARB is just another kind of spring.

So yes, the scale will register the instantaneous force in full. Until the other end of the spring has a force on it, there can't be any energy stored... ...because the spring doesn't compress until it does.

I've re-checked the speed of propagation of shear waves in steel, and it is still ridiculously high: 3250 m/s. So if you begin twisting a meter long ARB, the other end starts transmitting the force to the link 3 ten thousandths of a second later.

I sense, however, that this is all getting somewhat academic, given that we are agreed that different length arms on the ARB isn a good idea!

Agreed.

[john f]

Tim, let me try one more time.

It is impossible for the spring to store any energy unless there is a force acting on it on BOTH ENDS. An ARB is just another kind of spring.

So yes, the scale will register the instantaneous force in full. Until the other end of the spring has a force on it, there can't be any energy stored... ...because the spring doesn't compress until it does.

I've re-checked the speed of propagation of shear waves in steel, and it is still ridiculously high: 3250 m/s. So if you begin twisting a meter long ARB, the other end starts transmitting the force to the link 3 ten thousandths of a second later.

What he said.

john f

[tlracer]

Okay, last post on this (from me, anyway):

I have never said, implied (or intended to imply) that the applied force is unilateral. Indeed I am very well aware that to suggest so would contradict Newton's Third Law.

Nevertheless, when twisted, the ARB DOES store energy. It retains that energy until conditions change such that it can un-twist.

[alangbaker]

Okay, last post on this (from me, anyway):

I have never said, implied (or intended to imply) that the applied force is unilateral. Indeed I am very well aware that to suggest so would contradict Newton's Third Law.

Nevertheless, when twisted, the ARB DOES store energy. It retains that energy until conditions change such that it can un-twist.

Tim, that falls into the category of true but irrelevant to the issues at hand.

You started with "won't transfer the whole moment"...

...went to "transfer is delayed"...

...to "it modulates" it.

It does none of those things. The force you apply at one end of an ARB is matched by a force it applies to the link at the opposite end essentially (allowing for the speed of shear waves in the steel) instantaneously. It muddies the waters to start talking about the energy that is stored as if it had some effect on the torques and forces.

[john f]

Okay, last post on this (from me, anyway):

I have never said, implied (or intended to imply) that the applied force is unilateral. Indeed I am very well aware that to suggest so would contradict Newton's Third Law.

Nevertheless, when twisted, the ARB DOES store energy. It retains that energy until conditions change such that it can un-twist.

I do not think that anyone is arguing that there is not energy stored in a swaybar when it is twisted. The "argument" has been that for a force at one end of the bar, there is an equal and opposite force at the other end,and that it is instantaneous. I believe that you have been implying that part of this force in consumed in the twisting and therefore not the same amount is available at the other end. Your quote:

"I don't disagree; indeed I am quite certain that unequal ARB lever settings will result in handling differences side-to-side.

With hindsight, perhaps the word 'delay' was not the best; substitute 'modulate', such that the energy stored, as the input force twists the bar, means there is not 100% transfer to the other end."

I am disagreeing with this later part of your statement, only. And yes, the car will handle different turning different directions. Peace

john f

[tlracer]

Ah, now I see the confusion! In my attempt to be succinct it was possible to think I was referring to the force; not so, since Newton wouldn't allow...

...it is the energy input, on bump, that is not fully transferred since some of it is stored at the ARB twists.

In roll, such that the sprung part exerts a moment pivoting on the roll axis, I suspect unequal ARB levers will mean the side with the longer lever will experience greater displacement than the side with the shorter lever.

[billtebbutt]

.....that the difference in how a race car handles between left and right turns is determined more by a driver's relative muscle vs. fat mass ratio in his left buttock between his right buttock (or, vice versa), and that this differential is more material to real life in-turn car behavior than immaterial differences in anti-roll bar arm length?



bt