Math for track bar length

[xj92]

Anybody ever done the math to figure out the exact length you would need on a custom track bar or have the formula handy? Or another way to put it, when drilling a new hole, how much longer the track bar needs to be? I know how to do it manually, but I'm building a custom track bar this weekend and if I could remember my trig I'd figure it out on my own. It's going to be a fixed track bar for a 2" lift. The stock TRE wore out, so I'm putting a RE frame-side bracket on and welding a small RE joint onto the end of my stock track bar where the tre used to be. Might as well make it the correct length while I'm doing it.

 

[yossarian19]

Here ya go... worked this out a while ago...

Ok. Here we go...
Assuming the axle shifts to drivers side, which I think it does, and you measure with the point of the triangle going left towards passenger's side...
You know, or can find out, the vertical distance from frame side mount to axle side mount. Call this distance "A". The length of the track bar is "C" and the horizontal distance from frame side mount to axle mount is "B".
The frame side mount, the axle mount & that vertical difference make a triangle. Pythagorean Theorem works pretty well and it tells us that A squared plus B squared equals C squared, or a2+b2=C2
So, what I'm thinking is this: Measure A, B & C.
Measure how far your axle needs to be moved over. You could pick a common bolt on either side & hang a plumb bob from it, then measure distance from disc rotor to bob on each side. Lets say you need to move it over 3/4".
Add 3/4" to "B", use "A" as it is (because ride height hasn't changed) and re-calculate what "C" must be. This is your new eye-to-eye track bar length - so bend everything to clear, give yourself as much adjustment as you can going both ways and call it a day.

 

[shortxjdoug]

formulas are good but you cant beat measuring.....it seems like a lot of work to build a piece that your just gonna toss when you change the heigth of the jeep though

 

[xj92]

Shortxjdoug
1. I like the cleanliness, simplicity, & cost of a non-adjustable piece for something that will remain at just one ride height.
2. I can cut & weld, so if I did change the ride height, worst case scenario would be to modify the length again in the future or reuse the RE joint on another bar, not just toss it.
yossarian19
3. The Pythagorean Theorem will work, but I'm also looking for the formula using sin, cos, tan, or whatever that takes into account the angle & the arc with a certain vertical movement. If I can't figure it out before I start building it, I'll just use the Pythagorean Theorem or just manual measurements. Thanks for the reply.

 

[yossarian19]

Hahahah I know there is a better way to do it that involves fewer steps than constantly adjusting & re-assigning values to every little variable...
The thing is, I got pulled from public school when I was 16 and missed a helluva lot of math classes even when I Was going...
Good luck finding the trig - and if you do, post it up!

 

[Goatman]

Shortxjdoug
1. I like the cleanliness, simplicity, & cost of a non-adjustable piece for something that will remain at just one ride height.

Most would say that about an adjustable track bar.....and add utility. As a basic life principle, that easily bleeds over to buidling cars, having more options is always better. Since you're already building, adding options at this time simply makes good sense.

And then you don't need the trig. Actually, a string and chalk on the garage floor would be easier and quicker.

 

[yossarian19]

I actually have to back Goatman up here.
I've been reviewing trig online and applying it (in my head) to the problem at hand... There is so much measuring & adjusting numbers & generalized "bull" involved with working it out mathematically, I think you'd be better off buying an adjustable and doing it with a tape measure & some string. You could get it "almost" just by eyeball and "dialed" with a tape measure and 20 minutes.
I don't think I'd have all my *variables* worked out in the time it would take you to get it dialed in the "stupid" way. Especially since I don't have the coils I'm planning on, new TB mount, etc...
This all makes me wonder which way is actually the "smart guys" way to figure it out..

 

[vetteboy]

You could get it "almost" just by eyeball and "dialed" with a tape measure and 20 minutes.

I would even go so far as to say you could get it "well beyond good enough" by eyeball and a plumb bob.

 

[xj92]

I'm not hooked on overthinking it, but I was stuck at work in front of a computer earlier, and I figured if I could determine the exact length beforehand, ah how grand and easy life would be. I gave up on the math and just yanked the track bar once I got home. I measured my stock bar (mj) and my adjustable bar that has been dialed in on my xj with 4" so I know it needs to go somewhere in between there . I don't feel like buying & hanging plumbs, so eyeballing it should work out fine.

 

[markaboo929]

I'm not hooked on overthinking it, but I was stuck at work in front of a computer earlier, and I figured if I could determine the exact length beforehand, ah how grand and easy life would be. I gave up on the math and just yanked the track bar once I got home. I measured my stock bar (mj) and my adjustable bar that has been dialed in on my xj with 4" so I know it needs to go somewhere in between there . I don't feel like buying & hanging plumbs, so eyeballing it should work out fine.

Why buy a plumb bob-use a 3/4 nut or washer and a piece of string.That's the "stupid" way!:wierd:
3/4 becuase I was just looking at my 3/4 hiems!!!

 

[yossarian19]

Ok, this brainiac gives up -
whats the plumb bob for?

 

[xj92]

Just makes it easier to judge the axle's position in relation to the body. If you attach one on each side hanging straight down it's easier to judge when the axle is centered. I cut off the TRE tonight and started welding it. I'll probably finish it tomorrow.

 

[WrenchMonkey]

Ok, this brainiac gives up -
whats the plumb bob for?

I assume to drop a true vertical from each fender, as a pair of reference points to center the axle between.

The Pythagorean Theorem will work, but I'm also looking for the formula using sin, cos, tan, or whatever that takes into account the angle & the arc with a certain vertical movement...

Actually, the pythagorean is what you want. Run-squared, plus rise-squared, is your trackbar-length-squared. (Measure the rise and run before the lift, then add the lift height to the rise, and do the math.)

The trigonometry would only be helpful if you were concerned with the angle of the trackbar. You could use the rise and run to determine the bar's end-to-end angle: [arctan(rise/run)]. Or, if you knew what the new angle would be (you don't), you could figure the length based off the rise or run: rise/sin(theta), or run/cos(theta).

But you don't know or really care about the angles.

You just want the length.

:lecture:

Robert

 

[leftlanetruckin]

damn, i just make it so it is directly behind the draglink and as long as possible with the mounting options. i have 37's on 6.5" of lift and its daily driven with zero bumpsteer.
after reading all this though, i will just have to rip it all apart and steal one of the kids expensive calculators and redo it all from scratch.:shhh:

martin

 

[WrenchMonkey]

after reading all this though, i will just have to rip it all apart and steal one of the kids expensive calculators and redo it all from scratch.:shhh:

martin

I didn't say you really should work through all that mess, just that you theoretically could, if for some bizarre reason you really wanted to...

Robert

 

[leftlanetruckin]

I didn't say you really should work through all that mess, just that you theoretically could, if for some bizarre reason you really wanted to...

Robert

thanks robert, you just saved me 2 days of work and 3 bottles of asprin mate:laugh:

martin

 

[veedubshafer]

With my mangled fenders the plumb bobs would be a waste of time!