Steering is darting is this the likely culprit?

[joshua]

Yes. It's a common method.
But the key is to make it long enough to mimic the diameter of the tire that will be used.
The more common driveway method (I believe) is to use the sidewall of the tire. I've done it too, but I find that too many truck tires have too many sidewall discrepancies that can skew the numbers.

That said, for me it doesn't really matter, as no matter what I set it at, any time I'm doing a vehicle for the first time, I take what I set it at, drive it for awhile, then tweak it slightly over the next few weeks until I find where it likes it best.
It's usually where I set it initially, but not always.

Can't you use the bolt that's in there now?
Nothing wrong with coarse thread at least for initial driving around. If it's determined that the added strength of a fine-thread bolt is worth it, then by all means change it back out as soon as you can get the correct bolt.
Probably more important getting one with the correct length shank?
But I would not hesitate to use what you have in the short term.

Paul

It was welded in. (3/4 bolt) And would be a ton of work with a dermal to remove.

And I’m going to try the tape on the lugs method now that I understand it. I’ll report back later.

As I’ve currently switched projects to rebuilding my heater box cuz I’m in the frozen north of MN. Well kinda frozen as it was over 70 today.

 

[SLOWnEASY]

One of the alignment shops in San Diego does something similar. But they jack the up each wheel one at a time. With the wheel in the air they place a can of white spray paint on the ground close to the tire. Then they hold down the spray button and spin the tire by hand painting a line all the way around the circumference. Then while still spinning the tire they put a pointer on the ground and scrape a clear spot in the center of the line all the way around the tire. From there you have a consistent point to measure off of front and back.
I've used them since 1985 and typically the majority of the paint line wears off in the first 10 or so miles. You could also jack each tie up and spray a line of black to cover the white it you really want to.
Thinking further you could wrap a line of painters or even duct tape around the tire first and then use a fine point sharpie to draw a line around the tire. Just don't try to freehand the line. Hold the marking instrument on the ground and spin the tire. Oh and it probably goes without saying but for the marking, spin the tire away from the instrument so the pointer bounces off and doesn't grab the edge of a tire lug.
Editing since I just re-read Joshuas last post. You could definitely use just two pieces of tape one on the front and one on the back of the tire. But still find a way to hold your pen or sharpie steady and spin the tire to draw the lines.

 

[Broncobowsher]

I have heard of the scribe a line method as well. If you use spray crack check developer (talc powder suspended in alcohol) it will wash off.

 

[DirtDonk]

One potential issue with using the sidewalls is random bulging here and there, potentially skewing the measurements.
I get how that using a method that makes it an easy one-step (after other multiple steps?) measurement, would be appealing. Instead of creating a full round mark, or using two separate marks then, using one single point on the sidewall would at least keep it consistent.
We used to make our own measuring devices out of wood that put brackets up against the sidewalls of tires and mimicked a very large tape measure. Essentially a sliding scale arrangement.

Ours was a straight 2x2 with a vertical piece on one end, and a sliding pieces for the other. Long enough to reach the outside of the tires, a printed scale on it's surface (or an actual measurement tape/strip glued, screwed or stapled to the surface) was a nice repeatable tool capable of measuring any vehicle with any tire size. As long as the main beam was long enough of course.
Stood in the corner of our garage for 40 years and was put to good use in that time.
It started to lose favor with me though, when over the years it seemed like more and more tires (both car and truck tires) were coming with uneven sidewall surfaces.

But I still like the single piece of tape on a lug with a nice flat side to hook the tape measure to, or a single mark on the sidewall and roll the tire forward to take the second measurement. Still easy for one person to do it that way.

Paul

 

[.94 OR]

One potential issue with using the sidewalls is random bulging here and there, potentially skewing the measurements.
I get how that using a method that makes it an easy one-step (after other multiple steps?) measurement, would be appealing. Instead of creating a full round mark, or using two separate marks then, using one single point on the sidewall would at least keep it consistent.
We used to make our own measuring devices out of wood that put brackets up against the sidewalls of tires and mimicked a very large tape measure. Essentially a sliding scale arrangement.

Ours was a straight 2x2 with a vertical piece on one end, and a sliding pieces for the other. Long enough to reach the outside of the tires, a printed scale on it's surface (or an actual measurement tape/strip glued, screwed or stapled to the surface) was a nice repeatable tool capable of measuring any vehicle with any tire size. As long as the main beam was long enough of course.
Stood in the corner of our garage for 40 years and was put to good use in that time.
It started to lose favor with me though, when over the years it seemed like more and more tires (both car and truck tires) were coming with uneven sidewall surfaces.

But I still like the single piece of tape on a lug with a nice flat side to hook the tape measure to, or a single mark on the sidewall and roll the tire forward to take the second measurement. Still easy for one person to do it that way.

Paul

Any reason that method couldn't be modified to set against the rim instead of the sidewall with some offsets? Should eliminate the "bulge" issue that way.

 

[Broncobowsher]

I don't trust rims to be true.

Any good alignment machine has wheel sensors installed and the wheel rotated. This zeros out any runout and gets down to the true rotational axis of that tire. You could have wheels that look like Clark Griswold after paying $500 for 4 bald tires and a toe and still get an accurate alignment.

 

[DirtDonk]

Any reason that method couldn't be modified to set against the rim instead of the sidewall with some offsets? Should eliminate the "bulge" issue that way.

Nope, that would probably be more consistent than a tire sidewall.

 

[DirtDonk]

I don't trust rims to be true.

Probably not an uncommon thing. Especially if used hard.
But I generally do trust most wheels to be at least fairly true.
Certainly many of them won’t be too far out, and hopefully better than the tires!
And I’d want to know about it anyway. Would hope to replace them if I found them to be out of true.