Asked Chat GTP for track bar advice

[GreyZ]

This is hilariously wrong though. Wheel base and track bar length are not correlated. Its just chatGPT makeing up information.
This is the more correct equation. Still not exact, but much closer.
Lnew = sqrt(ΔH^2*Lold^2)
Lnew = new track bar length
Lold = old track bar length
ΔH= height change.


Regardless, changing the track bar is a bandaid for the correct answer and will result in different left to right roll centers of the rear axle. The rear trackbar should be as level as possible. Always. So if you lift 2", you need a 2" relocation bracket on either chassis side or axle side.


Don't trust chatGPT because it is wrong.

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[87-Z28]

This is the axle motion math from track bar that makes sense to me. Track bar length (Lo) is 44” and track bar height (Ho) is about 3” on my rig at ride height. Ho will vary based on lifted configuration. I am close to SAS lift.

track bar sweeps an arc and moves axle left to right as axle moves up and down. Figure attached shows later motion of axle (negative is towards drivers side). Notice as axle moves up it also moves towards passenger side, until track bar is perfectly horizontal (3” of vertical motion for me). Then axle will begin to move back to drivers side. It sweeps an arc.

a 2” lift for me will move axle down 2” wrt frame and cause <0.2” of axle movement towards drivers side. Very minimal lateral axle movement.

 

[MyDogGoldie]

Just came across this thread. I do not understand how track bar length is related to wheel base???

Sure the wheel base affects dynamic response of suspension and lateral loads on rear axle, which are carried by track bar. However the track bar length sweeps an arc in a vertical plane through the rear axle axis. Changing lengths moves axle left or right based on track bar angle in that plane. Not seeing how this is related to wheel base. Track bar sweeps a large arc and angles are small. Cosine of small angles with large arc shifts rear axle by small amount for 2-3” lift.

stretching bronco front end to >1000 ft, keeping rear identical but lifting 20”, should result in a large displacement of rear axle towards driver’s side. Formula suggests no effective displacement due to super long wheel base. Makes no sense.

@dgorsett and @BigMeatsBronco I saw you guys commented on another post about track bar lengths. Any thoughts on why include wheel base?

I can tell you this,,, I called ICON and they said a rule of thumb is 1/16" track bar adjustment per 1" lift adjustment.

I agree the AI track bar formula is wack. Wheelbase??? Makes no sense.

 

[87-Z28]

I guess we don’t need to worry about being run over by artificial “intelligence” anytime soon.

 

[87-Z28]

I can tell you this,,, I called ICON and they said a rule of thumb is 1/16" track bar adjustment per 1" lift adjustment.

I agree the AI track bar formula is wack. Wheelbase??? Makes no sense.

The relationship is non linear, but from the curve above… a typical 3” icon lift moves the axle maybe 0.3”, so 3/16 for rule of thumb is about 0.2”. Seems reasonable rule of thumb. But just not likely very necessary. These are small numbers.

probably best to have track bar as horizontal as possible. Track bar resists lateral loads from axle. So any vertical component of loading will result in uneven rear axle roll when turning left versus right. Best to minimize vertical track bar loads by keeping bar nearly horizontal.

but none if this is likely necessary for a minor 2” lift. Both axle shift and vertical loading are small numbers.

 

[87-Z28]

Asymmetric rear track bar vertical load can produce unintended consequences for suspension. Track bar resists lateral loading of rear axle and will induce some corresponding vertical loads, since bar is not perfectly horizontal. Ratio of vertical loads to lateral is proportional to track bar angle and linear wrt lifted ride height.

figure shows rear axle vertical to lateral loading ratio as related to ride height for my OBX which is sitting near SAS lift. So 0 lift in figure represents near SAS ride height, which produces <10% vertical load component. Notice a 4” lift starts generating significant vertical loading. Increasing track bar length helps to re-center axle but does not decrease vertical loading. Since track bar angle has not changed. Track bar relocation to near horizontal is required to reduce vertical loading.

 

[telenerd]

Morning. The track bar had to be shortened on mine to get axle aligned correctly for my almost 2 inch lift. Alignment shop was able to get the axle centered and thrust angle dialed in.

Thoughts? So reading posts, lengthening the track bar for lift is not what you want?

 

[87-Z28]

Track bar with stock mounting locations will kinematically move the axle towards drivers side as rear body is lifted. To center axle then the bar must be lengthened.

track bar with relocation bracket is a different story. As bar becomes more vertical it must become shorter to center axle. Shortest bar length kinematically occurs when it is perfectly horizontal.

 

[telenerd]

Track bar with stock mounting locations will kinematically move the axle towards drivers side as rear body is lifted. To center axle then the bar must be lengthened.

track bar with relocation bracket is a different story. As bar becomes more vertical it must become shorter to center axle. Shortest bar length kinematically occurs when it is perfectly horizontal.

Not sure I completely understand. If the axle is shifted to driver side from a lift the track bar would need shortened to pull the axle in to the passenger side. Isn’t that right?

 

[87-Z28]

Not sure I completely understand. If the axle is shifted to driver side from a lift the track bar would need shortened to pull the axle in to the passenger side. Isn’t that right?

no that is not correct. I added a figure to my response to illustrate the kinematics.

 

[telenerd]

no that is not correct. I added a figure to my response to illustrate the kinematics.

Thanks maybe I miss heard the alignment tech. I will double check the axle center with a straight edge on the tire and compare length to the body/frame.

 

[87-Z28]

Thanks maybe I miss heard the alignment tech. I will double check the axle center with a straight edge on the tire and compare length to the body/frame.

I thought that you also had a relocation bracket and are now fairly horizontal with the track bar. If so it is definitely possible to have needed to shorten your bar length. Shortest length occurs at pure horizontal position.

 

[telenerd]

I thought that you also had a relocation bracket and are now fairly horizontal with the track bar. If so it is definitely possible to have needed to shorten your bar length. Shortest length occurs at pure horizontal position.

Actually I chose to not use a relocation bracket. Saw too many articles on Jeeps and Broncos of them cracking.

 

[telenerd]

Okay I nerded out today after work. Lengthing the track bar moved the axle out to the driver side. Shortening it moved the axle to passenger side. Did a measurement from the frame to edge of the back of the tire. My track bar was only off by one turn to the passenger side, was a bit too short. I used a straight edge and block of wood. Thoughts? Cowboy way of doing it.

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