How to align your Jeep Wrangler TJ

The 1/16" alignment for all tire sizes always bothered me. The math doesn't work.
I read through all 18 pages and was glad to see @TJim stuck to his guns (around post 300) and showed why it doesn't work.
1/16 to 1/8 might be close enough for most, especially if you're not very accurate with your measurements.
Even if it's wrong, it might be better than what you started with.

https://robrobinette.com/ConvertToeInchesToDegrees.htm

That is because it doesn't work for all tire sizes. 1/16" toe in only works for a 35".
 
A toe angle is a toe angle, whether there is a larger or smaller tire sitting there. The only thing the tire diameter matters for is when you're measuring on the tire. Without tires, you're just measuring the angle of the axles/rotors. Measuring at 24" (12" ahead of axle, 12" behind axle) a difference of 1/8" gives you the correct angle (0.15° each side, 0.30° total). At 35.75" a difference of 3/16" gives the same angle. And yes, the math does work. 24 * sin(0.30) = 0.125
 
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A toe angle is a toe angle, whether there is a larger or smaller tire sitting there. The only thing the tire diameter matters for is when you're measuring on the tire. Without tires, you're just measuring the angle of the axles/rotors. Measuring at 24" (12" ahead of axle, 12" behind axle) a difference of 1/8" gives you the correct angle (0.15° each side, 0.30° total). At 35.75" a difference of 3/16" gives the same angle. And yes, the math does work. 24 * sin(0.30) = 0.125

Or you can use a pair of sticks to mimic a 35" tire. The only reason 1/16" on a 35" was used so often is because it is common and easy to remember. Then some people forgot how geometry worked and started saying 1/16" for all tire sizes.
 
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Why do you keep saying that?
1/16 was for stock tires (I think).
3/16 was recommended for 35s.

Nope, 1/16" (total) is for 12" tires. The only TJs running 12" tires are in the Unfortunate TJ of the Day thread. :)

And if you're saying 1/16" per side, total of 1/8", that is correct at 24" — good for 24" bars, but still tiny for a TJ tire.
 
Appreciate all the info in this thread and the discussion. I have 31 inch tires on my TJ and first set my toe in at 1/8 inch. It seemed ok but still seemed to wander a little. I then set it to 3/16 and that's perfect. It's not a major difference but I can feel it when driving. I'll stick with the slightly more toe in and if it wears my tires a little more, I'll just replace them a little sooner.
 
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Great thread here. I have been a mechanic for over 40 years. I originally learned how to set tow in on my dad's 73 gmc suburban. We would spin a front tire and make a line around the tire, then do the other tire and then measure front to rear on the lines and adjust. Dad used to like 0 for toe in and I did that for a long time with good results.
Fast forward a lot of years to 2020. I purchased a alignment rack for the autoshop that I supervised and decided it was time for me to fine tune my alignment abilities. I had some bad luck with alignments on my 2002 Duramax 2500 and noticed pretty bad tire wear and poor driveabiltiy. I did find a GM dealer that had a really good alignment tech who got my truck running true again after I had replaced all of the steering components. To be good at alignments is an art, and toe in is only a small part of it. The ultimate goal is driveability and tire wear. With a Jeep TJ driveability is number 1. My TJ drove like crap when I purchased it! What I found was all of my Currie Johnny Joints were worn out due to lack of grease. I replaced balls and outer urethane and got them good and tight. I set my toe close to 0 like I had always done with my solid axle 4x4's and the Jeep was still squirelly going down the road. When I received the new alignment rack at work, the first vehicle to get checked was my Jeep TJ. The first thing I noticed was my thrust angle was WAY off, close to .7 degrees by memory. My rear adjustable links were all set to even length side to side. To fix this issue I had to shorten the links on the driver side of the rear axle by close to .250 inches. Now the thrust angle was within spec. Then I double checked the axle placements by dropping a plumb bob from frame hole locations and measuring to the axle tubes. All was now good. I moved on to the front axle. Camber was slightly negative, but within spec so I left it. Caster is extremely important on a 4x4 with big tires and my caster was only about 5 degrees. I adjusted the links and got the caster close to 7 degrees. Then I moved on to toe in.
Working with the alignment machine I set my toe in close to 0 and test drove. Still had a lot of wander. I ended up close to factory spec on toe which comes out close to 3/16 when double checked with my quick trick alignment bar. Driveability is much better now but it has been a long process. I think my rock ram also adds to a little steering sensitivity due to very little steering wheel input moves the Jeep. At this point my 35 inch Mickey Thompson MTZ's are wearing very evenly.
I will add a little to this thread that after I had access to the new alignment rack I decided to align my 2017 Duramax 3500 that I had lifted the front end about 2 inches. My first attempt was a total failure! The truck pulled hard to the right going down the road. Again I tried staying close to 0 degrees of toe in, but the camber and caster kicked my butt. I learned a little bit about cross caster which involves setting the caster to a different spec on one side as opposed to the other and this can have a big effect on pulling going down the road. We don't have to worry about this on the Jeep TJ platform. When I finally WON on my truck, I set the toe in at factory spec which is fairly broad, but I went with minimum acceptable toe in and got caster and camber in spec and now my truck drives very well. What I did notice was when I had my toe set at close to zero I ended up with quite a bit of steering wander that wasn't there when I started. I will also add, that toe really doesn't seem to affect tire wear a lot, but out of spec camber will wear your tires in a hurry. I really don't care what measurement I need to go with in regard to a number like toe in. I want repeatability after I find the best setting for my vehicle that is far from stock. Find what works for your Jeep and stay with it. If you have bent something and you are 1/2 inch off on toe, fix it, but I wouldn't get hung up on the difference between 1/16-1/8-3/16, set it drive it and quit when you are happy with the results. And don't forget air pressure too on driveability. I am set on 24 psi on the road now with my 35's. More pressure equals better fuel economy, but less stability. Having a alignment rack to experiment with taught me a lot and unfortuneately some of what I learned I can't remember without looking up in a alignment manual because I don't do this every day, especially now that I am retired.
 
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I apologize if this is a dumb question or if it was covered somewhere in this thread (I've only read about half the pages). I have 225/75/15 tires. I calculated my tire height to be 28.3 inches. For this alignment process, do I use this exact figure when making the marks on the aluminum bar (14.15 inches from center on each side), or do I use 28 inches (14 inches from center)? Thanks.
 
I apologize if this is a dumb question or if it was covered somewhere in this thread (I've only read about half the pages). I have 225/75/15 tires. I calculated my tire height to be 28.3 inches. For this alignment process, do I use this exact figure when making the marks on the aluminum bar (14.15 inches from center on each side), or do I use 28 inches (14 inches from center)? Thanks.

14 inches from center is what I would use. The difference is irrelevant.
 
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I apologize if this is a dumb question or if it was covered somewhere in this thread (I've only read about half the pages). I have 225/75/15 tires. I calculated my tire height to be 28.3 inches. For this alignment process, do I use this exact figure when making the marks on the aluminum bar (14.15 inches from center on each side), or do I use 28 inches (14 inches from center)? Thanks.

No, make your marks at 12” from center on each side of your aluminum bar (total of 24” between the marks) and set your toe at 1/8” total.
 
No, make your marks at 12” from center on each side of your aluminum bar (total of 24” between the marks) and set your toe at 1/8” total.

Can you please explain why 12" and not 14"? I thought the process is to measure out 1/2 the height of the tire in each direction from the center of the aluminum bar. My tire height is 28.3" by my calculation. Thanks.
 
Don’t over think it. The alignment on these Jeeps is not an exact science although some try to treat it as such. I have 31 inch tires. I marked 15.5 inches from center and ultimately set mine at 3/16 inch toe in. Works great for me.
 
Tire size is utterly irrelevant for setting toe, unless you're actually using the soft rubber balloon to measure on (which is dumb). The toe angle is the same whether you have 12" tires or 44" tires.
 
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Can you please explain why 12" and not 14"? I thought the process is to measure out 1/2 the height of the tire in each direction from the center of the aluminum bar. My tire height is 28.3" by my calculation. Thanks.

Because of what @OldBuzzard said. Tire size is irrelevant. It's an angle. If you want the same angle but different mark placement you can do that. For example.

3/16" toe in with marks at 17.5" from center on each side ~EQUALS 1/8" toe in with marks at 12" from center on each side.
 
this shit cracks me up :ROFLMAO:

I know, right!

How can we be on page 19 of setting toe in?

Oh yeah, because it was f---ed up on page 1 and not fixed till blaine on page 8, and now a million iterations.
 
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Thanks for the replies. I understand what I need to do now. I'm not sure why, but kind of reminds me of measuring the dwell angle when adjusting the ignition points on my '65 VW. I've always understood that the dwell angle is more accurate than the points gap measured in fractions of an inch.
 
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Before I ask this question, I'll admit I'm an over thinker.

I'm about to do the ZJ tie rod upgrade on my '06 TJ. I understand the process described here to set the toe in afterwards. But, I looked at the toe in adjustment procedure in the FSM and it talks about adjusting the toe on each wheel independently.....passenger side from the drag link sleeve at the pitman arm and driver's side from the tie rod sleeve at the wheel. Seems like the procedure described in this thread would only adjust the driver's wheel. But, when adjusting the steering wheel at the drag link as described, wouldn't that also impact the toe in of the passenger wheel?