Currie Antirock has allowed me to climb easier (am I imagining this?)

[SvtLdr]

Most sway bars are torsional springs. The stock sway bar is a thick bar that significantly resists twisting. The Antirock simply has a much smaller diameter or softer torsional spring, allowing for less resistance to axle flex. The arms are the levers that act upon that torsional spring.

The Swayloc combines an Antirock style torsional spring with a much heavier pipe, and engages the pipe when the heavy setting is selected.

A torsional spring operates like a normal spring in that the applied force generally increases linearly with increased deflection, except that the resulting force is torsional, not axial. The arms of the sway bar convert that torsional force into axial force which is then applied through the links to the axle.

So a soft sway bar might only apply say 10lbs up on one side and down on the other when deflected 1”, but a stiff one might do 30 lbs. Increase the deflection to 2”, and those numbers become 20 and 60 lbs, respectively. (These numbers are made up for this example.)

The Antirock simply only has one thin torsion bar with an overall soft rate. The Swayloc is the same except that it can also engage a much stiffer and fatter bar to fight deflection.

The arm length also plays into stiffness, which is why the Antirock and Swayloc have multiple holes to adjust stiffness. The longer the lever arm, the less force is required to deflect the torsion bar, and the softer the effective rate of the sway bar will be. Much like how a long breaker bar turns a socket more easily than a stubby ratchet.

That effect of arm length on stiffness can also be used to asymmetrically set a sway bar. If one arm is set longer than the other, the longer arm side will dominate the shorter side because the longer lever arm can more easily apply torsion to the bar.

The torsion bar itself is constrained in 5 dimensions. It cannot move up, down, side to side, forwards, backwards, or in the roll or yaw rotations relative to the frame. It however is free to rotate and deflect in the pitch rotation, subject to the constraints of the arms of the sway bar.

This means that the sum of the torques about the bar must be zero to prevent the bar from rapidly spinning in its bushings. Therefore, the torque applied to one bar must equal the torque applied to the other bar with opposite direction. So two equal length arms will provide equal but opposing forces to the axle. (Two unequal length bars will still have the same torque, but different forces because of the different lever lengths.)

I figured someone would chime in with "the rest of the story". Well said, sir!

 

[andy29847]

That effect of arm length on stiffness can also be used to asymmetrically set a sway bar. If one arm is set longer than the other, the longer arm side will dominate the shorter side because the longer lever arm can more easily apply torsion to the bar.

Your post was informative and well written. Thanks for sharing. My thoughts are that the forces transmitted by arms of different length through the bar remain the same because the levers are acting in concert (same torsion bar) with each other. Fifty pounds input on one side will produce 50 pounds out on the other side. The length of the movement on each side will be different. What that nets in suspension effectiveness the big question. I still think everything will average out - 3 + 5=8, 4 + 4=8.

 

[Chris]

@Irun, I have both the old style Antirock and the new style. I compared the arms side-by-side the other day when installing them, and the arms are identical in length. The ONLY difference I can see is they got rid of the forward most two holes on the new Antirock, most likely because no one was using those settings as they would be extra stiff.

 

[Steel City 06]

Your post was informative and well written. Thanks for sharing. My thoughts are that the forces transmitted by arms of different length through the bar remain the same because the levers are acting in concert (same torsion bar) with each other. Fifty pounds input on one side will produce 50 pounds out on the other side. The length of the movement on each side will be different. What that nets in suspension effectiveness the big question. I still think everything will average out - 3 + 5=8, 4 + 4=8.

The axial reaction force is actually not provided by the other arm, but instead the bushings at the end of the bar. So if you have 50 lbs pushing on one side, the opposing 50 lbs is actually coming from the bushing and is being transferred through the frame. So there is no need from a free-body perspective for the axial force on one arm to equal the force on the other. However, there is a need for the torque on the torsion bar to match, as the bushings do not provide any significant torque to the bar.

Imagine a seesaw with unequal length sides (pretend it is balanced while unloaded). If one kid sits on the short side, and another on the long side, the kid on the long side has to weigh less to keep the seesaw balanced. The reaction force to prevent the seesaw from accelerating to the center of the earth is provided by the hinge, and not the opposing weights of the kids.

In the example of the Antirock, if unequal length arms are used, the remaining force is actually transferred through a net uplift or down pressure to the frame relative to the axle.

Imagine we have an Antirock with one 12” arm and one 24” arm. If I apply 20 lbs upwards to the long end perpendicular to the arm, the bushing reacts by providing 20 lbs downward to the bar. Simultaneously, the torsion bar is loaded with 40 ft-lbs of torque. That torque is then transferred to the opposite (12”) arm.

Now, in order to cancel out that torque, the arm applies a 40 lbs upwards force on the axle (aka the axle pulls down with 40 lbs), and the bushing at that end of the torsion bar applies a 40 lbs upwards force on the arm. This creates the opposing 40 ft-lbs of torque to stop the bar from rotating.

So even though you only have two directly variable forces, you actually have a set of two additional non-zero forces required to keep the bar from rotating. If the bushings didn’t exist, the whole bar would simply rotate in the roll orientation and never apply any force whatsoever.

And in this case, since the forces applied to the axle are unequal (bar pulls up with 40 lbs and down with 20), the torsion bar also has the effect of sucking the frame down towards the axle with the force of 20 lbs. (The opposing reaction is then created by the more loaded coil springs.)

 

[NashvilleTJ]

I run the Sway-Loc, and one thing that I don't think has been mentioned is that both the anti-rock and the sway-loc support much more articulation than the stock sway bar. Once you create the ability for your suspension to articulate much more than stock, the stock sway-bar runs out of room pretty quickly. When using the sway-loc / anti-rock, the result is that the suspension is controlled over a much larger range of motion.

The sway-loc in the off-road (soft) setting is about the same as the anti-rock, but in the on-road setting it is stiffer than the stock sway bar greatly improving the street ride.

But don't try this flex with the sway-loc in the street setting - or you will bend a sway arm. Ask me how I know...

 

[jjvw]

Here's an old Rubicon commercial showing how little the factory front sway bar allows for articulation. Most of the movement is accomplished from the rear.

 

[andy29847]

The axial reaction force is actually not provided by the other arm, but instead the bushings at the end of the bar. So if you have 50 lbs pushing on one side, the opposing 50 lbs is actually coming from the bushing and is being transferred through the frame. So there is no need from a free-body perspective for the axial force on one arm to equal the force on the other. However, there is a need for the torque on the torsion bar to match, as the bushings do not provide any significant torque to the bar.

Imagine a seesaw with unequal length sides (pretend it is balanced while unloaded). If one kid sits on the short side, and another on the long side, the kid on the long side has to weigh less to keep the seesaw balanced. The reaction force to prevent the seesaw from accelerating to the center of the earth is provided by the hinge, and not the opposing weights of the kids.

In the example of the Antirock, if unequal length arms are used, the remaining force is actually transferred through a net uplift or down pressure to the frame relative to the axle.

Imagine we have an Antirock with one 12” arm and one 24” arm. If I apply 20 lbs upwards to the long end perpendicular to the arm, the bushing reacts by providing 20 lbs downward to the bar. Simultaneously, the torsion bar is loaded with 40 ft-lbs of torque. That torque is then transferred to the opposite (12”) arm.

Now, in order to cancel out that torque, the arm applies a 40 lbs upwards force on the axle (aka the axle pulls down with 40 lbs), and the bushing at that end of the torsion bar applies a 40 lbs upwards force on the arm. This creates the opposing 40 ft-lbs of torque to stop the bar from rotating.

So even though you only have two directly variable forces, you actually have a set of two additional non-zero forces required to keep the bar from rotating. If the bushings didn’t exist, the whole bar would simply rotate in the roll orientation and never apply any force whatsoever.

And in this case, since the forces applied to the axle are unequal (bar pulls up with 40 lbs and down with 20), the torsion bar also has the effect of sucking the frame down towards the axle with the force of 20 lbs. (The opposing reaction is then created by the more loaded coil springs.)

I respectively disagree. Sway bar bushing don't do anything but provide location for the sway bar. There may be some incidental forces as the suspension moves, but I believe that the rigidity of the frame makes those force inconsequential. Hence, sway bar location brackets are flimsy. Unequal arms = unequal movement - that is all. The forces of the axle are transmitted through the springs and shocks. Thank you for your response. You are probably the smartest guy in this room.

 

[mrblaine]

It sounds like that is what the sway loc does as the arms move independently when unlocked,

The arms on the right side only move independently once they disconnect from each other but at that point, the outer arm is working against the A/R size torsion bar. Connected back together, they work against both torsion bars.

 

[TJ Starting]

I run the Sway-Loc, and one thing that I don't think has been mentioned is that both the anti-rock and the sway-loc support much more articulation than the stock sway bar. Once you create the ability for your suspension to articulate much more than stock, the stock sway-bar runs out of room pretty quickly. When using the sway-loc / anti-rock, the result is that the suspension is controlled over a much larger range of motion.

The sway-loc in the off-road (soft) setting is about the same as the anti-rock, but in the on-road setting it is stiffer than the stock sway bar greatly improving the street ride.

But don't try this flex with the sway-loc in the street setting - or you will bend a sway arm. Ask me how I know...

View attachment 196389

How do you know?

 

[NashvilleTJ]

How do you know?

I’m glad you asked! I was once testing my clearance in the shop by raising the drivers side front wheel with an engine hoist. Not thinking, I had the sway-loc in street mode. Once I got the tire raised all the way up at full articulation, and while standing about a foot from the sway arm which at that point was above eye level, I watched as the 1/2” steel arm very slowly bent into a nice parabola. It took quit a bit of work on my 30 ton press to get it back in line. Lesson learned...

 

[TJ Starting]

I’m glad you asked! I was once testing my clearance in the shop by raising the drivers side front wheel with an engine hoist. Not thinking, I had the sway-loc in street mode. Once I got the tire raised all the way up at full articulation, and while standing about a foot from the sway arm which at that point was above eye level, I watched as the 1/2” steel arm very slowly bent into a nice parabola. It took quit a bit of work on my 30 ton press to get it back in line. Lesson learned...

Yeah, just messing with ya but very interesting none the less.

 

[Irun]

I really don't understand the confusion here. Stock sway bar, disconnected, moves up left side, no right side downward pressure. Result, traction minimized. AR moves up left side, downward pressure right side. Result, more overall wheel traction.

 

[DrDmoney]

Here's an old Rubicon commercial showing how little the factory front sway bar allows for articulation. Most of the movement is accomplished from the rear.

I think more than one of us has parked in that spot.

 

[Brianj5600]

I really don't understand the confusion here. Stock sway bar, disconnected, moves up left side, no right side downward pressure. Result, traction minimized. AR moves up left side, downward pressure right side. Result, more overall wheel traction.

I don't understand this, but willing to learn. With an AR when the left tire goes into bump the left spring effective rate is stiffer and the right spring rate is effectively softer. The right rear load will increase, but I don't see how the right front is pushed down.

 

[jjvw]

I don't understand this, but willing to learn. With an AR when the left tire goes into bump the left spring effective rate is stiffer and the right spring rate is effectively softer. The right rear load will increase, but I don't see how the right front is pushed down.

Think of it in terms of the sway bar working to keep the frame and axle parallel to each other. There is a tendency to overcomplicate what is going on, but it is this simple.

 

[Brianj5600]

I think I have a petty good grasp on how sway bars work. I just didn't understand Irun's explanation.

 

[Steel City 06]

I don't understand this, but willing to learn. With an AR when the left tire goes into bump the left spring effective rate is stiffer and the right spring rate is effectively softer. The right rear load will increase, but I don't see how the right front is pushed down.

The comparison should be between a stock connected swaybar and an Antirock, not a disconnected swaybar and an Antirock.

Any swaybar, be it stock, or Antirock, or Swayloc, is a type of spring used to resist sideways axle movement. Any swaybar will pull up on the low side tire and down on the high side tire, and create more pressure on the high side.

How much pressure it creates is determined by the stiffness of the overall swaybar system. A stock bar will provide significant resistance, often to the point that the low side tire lifts off the ground. A disconnected swaybar provides no resistance, and any flexural resistance is provided by the coil springs. An Antirock is merely a soft-rate bar that goes between a connected and disconnected stock bar. Thus it often prevents lifting tires while still having some control on body roll.

In addition, the front Antirock also helps transfer some of the motion that would cause the front axle to flex to the rear axle in opposition to that sway bar. Thus, an Antirock generally results in a better balance between front and rear than a stock connected or disconnected bar.

An Antirock would result in more force on the downside tire than a stock bar, but still less than a disconnected bar.

It really doesn’t force the down side tire into the ground. That would have to be done by the inverse of a swaybar, or basically a system that promotes divergent movement of the axle from level (I have never heard of one), or from an active suspension system (such as an AiRock).

 

[Steel City 06]

I respectively disagree. Sway bar bushing don't do anything but provide location for the sway bar. There may be some incidental forces as the suspension moves, but I believe that the rigidity of the frame makes those force inconsequential. Hence, sway bar location brackets are flimsy.

If this was the case, then the sway bar would simply rotate in the roll direction rather than flex or resist motion.

In order to remain static, the total forces in the X, Y, and Z axes must be zero. But the total moments in the roll, pitch, and yaw axes must also be zero.

If we model the arms as being in the X axis only, the links as being in the Z axis only, and the torsion bar as being in the Y axis only, then we have a roughly simplified model of the assembly.

The links can only provide a force in the z axis, and the bushings can provide significant reaction force in the x and z axes (the torsion bar is inside them) as well as incidental force in the y axis (the arms can rub up against the bushing).

There are no significant effective applied forces in the X and Y axes, so any reaction in the bushings will effectively be negligible. But there is an applied force in the Z direction from a sway bar link, which might be explained by the opposite reaction at the opposite sway bar link.

But we also have to make sure that the total moments are also zero.

Moment in the yaw direction will effectively be zero, as there are no significant forces applied in the X or Y axes.

Moment in the pitch direction has already been discussed, but in summary, the moment applied by a sway bar link on the sway bar arm about the pivot must be canceled by the moment on the opposite arm (resulting in applied force on the opposite link).

But moment in the roll direction must also total to zero. The force vectors in the Z axis are not at the same Y position, and also might not be at the same X position if the arms are of unequal length. And as the only other constraint available, this moment in the roll direction must be applied by the bushings themselves.

If one sway bar link pushes up with 20 lbs and the other down with 20 lbs, and the bar is 36” long (guess), there is an effective moment of 30 ft-lbs about the center of the swaybar in the roll direction. This moment can only be countered by the sway bar bushings, and if we pretend they are also 36” apart (they’re actually slightly closer together than the bars), then they will have to counteract the moment by applying 20 lbs down and up at either end to create the 30ft-lbs moment to cancel the roll moment applied by the sway bar links.

So to be effective, the sway bar bushings (or brackets) have to be able to take as much force as the links can provide. Without the reaction force of the bushings or brackets, the bar doesn’t twist - it merely pops up.

Here’s a different way of thinking about it - a sway bar resists roll in vehicles by applying a restorative twist to the axle. That twist must be reacted upon by something else, which happens to be the frame of the car. The sway bar merely creates an additional moment between the axle and the frame.

 

[Sj's TJ]

This is a case where I did a little experimenting. I used a real climb to test the settings.

Step 1 - Established a baseline climb, without the AR
Step 2 - Installed AR and set to 3, per suggestion from others. Made the climb several times, to compare to the original baseline.
Step 3 - Changed the settings to the last (5) setting and repeat climbs.
Step 4 - Change right side setting back to 3, but leave the left side set to 5, and repeat.

In all the climbs, the latter felt like the best balance. I noticed consistent traction, with minimal body roll. Admittedly, this could simply be an artifact of repeated climbs improved my driving skill and knowledge of lines, but I consciously tried to take the same lines, at the same speeds each time.

To balance this out, I repeated the exact same process for driving on the road. In the end, I landed on Step 4 above. One set to hole three, one set to hole 5. I don't know if this makes sense or not, but know my vehicle well enough to "feel" subtle differences.

Rich, when you say right side at hole 3, is that passenger side or driver's side? I have noticed a lot more tippyness on the passenger side since I've installed the AR.

 

[Jerry Bransford]

Rich, when you say right side at hole 3, is that passenger side or driver's side? I have noticed a lot more tippiness on the passenger side since I've installed the AR.

That is normally caused by soft or perhaps worn out shocks. I run my Antirock at its loosest setting and I drive it on tight twisty roads quite a bit, most of the time towing my pop-up tent trailer, and it handles fine. I'm running Rancho gas charged shocks.