Toe in VS Toe Out

[IanNubbit]

What's the basis of the assumption that otherwise straight tires push out instead of in when pushed forward?

The simple part I would say is becuase of weight on factory style back spacing. The face of the wheel is so far out, out it rolls.

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[mrmo]

Normal road thrust will tend to push them out

 

[Lunentucker]

So the theory of slight toe out preloads the outward flex and resists road energies from making one wheel move back inwards, thus mitigating the likelihood of the onset of the harmonic resonance that begins death wobble.
Makes a little bit of sense.

 

[ShadowsPapa]

From Steersmarts:

"Yes, the industry as a whole recommends .5˚ of toe-in. From the studies that we've conducted, we find that .5˚ of toe-out is what works the best with our products, as well as with countering any type of potential death wobble situation. Everyone is entitled to set things up however they see fit, but our recommendations are not just pulled out of thin air, they come for studies and research that we've done with setting the vehicles up in different ways.”

And their studies trump decades of studies by suspension experts in the industry for as long or longer.

What's the basis of the assumption that otherwise straight tires push out instead of in when pushed forward?

Scrub radius and the intersection of the angles as I posted earlier. I posted exactly when something will tend to toe out or in.

If scrub radius is positive (contact patch arc outboard of the pivot point), the wheels will try to toe out.

 

[Lunentucker]

I think the engineers who write the books and the engineers who design and build Jeeps, with numerous places and ways to get it wrong, should get together and go bowling.

Worded differently, the books assume everything is always tight and that it does not move in the joints.

 

[Burghardphotography]

And their studies trump decades of studies by suspension experts in the industry for as long or longer.

Im not saying either way, I just found that quote online and thought it would be useful here.

Don’t look at me, my rig is toed In!

 

[mx5red]

I think the engineers who design Jeeps and the factory workers who hand tighten tie rod bolts on Fridays, with numerous places and ways to get it wrong, should get together and go bowling.

Worded differently, the books assume everything is always tight and that it does not move in the joints.

Fixed it For ya

 

[IanNubbit]

And their studies trump decades of studies by suspension experts in the industry for as long or longer.


Scrub radius and the intersection of the angles as I posted earlier. I posted exactly when something will tend to toe out or in.

If scrub radius is positive (contact patch arc outboard of the pivot point), the wheels will try to toe out.

Just spit balling, is it possible some of these jeeps have negative scrub radius and would therefore naturally tow in?

 

[Jeepasaurus_Rex]

Well since we are on this topic. Does anyone have some tips for me to get my toe zeroed, or slightly in or out.. and ALSO my steering wheel straight?

I can never seem to get it where I want it. I know that it's possible.
porque no los dos!?

 

[Lunentucker]

Well since we are on this topic. Does anyone have some tips for me to get my toe zeroed, or slightly in or out.. and ALSO my steering wheel straight?

I can never seem to get it where I want it. I know that it's possible.
porque no los dos!?

Use a laser tape measure if you don't have a helper.
I posted a separate thread.
Tie rod sets toe and drag link sets steering wheel after you get the toe set.

DISCLAIMER:

 

[ShadowsPapa]

Use a laser tape measure if you don't have a helper.
I posted a separate thread.
Tie rod sets toe and track bar sets steering wheel after you get the toe set.

Close- drag link centers the steering wheel.

If the track bar is adjustable, center the axle first.
Next set toe with the tie rod.
Finally center the steering wheel with the drag link.
You can use JSCAN on your phone while you are under the truck to get the wheel centered.
Monitor the steering column degrees turned.
What I do is drive the truck on a flat straight road and use JSCAN to see what the angle of the steering column is while I am driving straight. If it's 2 degrees, I note that mentally.
Next, I park the truck in my garage so that the steering wheel is 2 degrees according to jscan.
Get under the truck with your phone. turn the drag link adjustment until the steering column number is 0 degrees.
That should get you really close.

 

[Lunentucker]

LOL. Yeah. That's one. I still get confused on them. The one near the front above the tie rod, with the twirler on it.

 

[IanNubbit]

Close- drag link centers the steering wheel.

If the track bar is adjustable, center the axle first.
Next set toe with the tie rod.
Finally center the steering wheel with the drag link.
You can use JSCAN on your phone while you are under the truck to get the wheel centered.
Monitor the steering column degrees turned.
What I do is drive the truck on a flat straight road and use JSCAN to see what the angle of the steering column is while I am driving straight. If it's 2 degrees, I note that mentally.
Next, I park the truck in my garage so that the steering wheel is 2 degrees according to jscan.
Get under the truck with your phone. turn the drag link adjustment until the steering column number is 0 degrees.
That should get you really close.

That's honestly the best way Ive seen to do that. Probably going to start doing that on warranty repairs instead of setting up the whole alignment machine lol.

 

[ShadowsPapa]

Just spit balling, is it possible some of these jeeps have negative scrub radius and would therefore naturally tow in?

Interesting thinking and I've pondered that - and I don't have the answer for whether or not these are positive or negative scrub as they sit STOCK.
However, the toe-in setting should be a clue. If these are set to factory spec which is toe in, and they would naturally toe in, you'd see feathering of the tires due to the increase in toe-in as you drive.
Guys and gals who put on different wheels to move the tires out move their trucks naturally toward positive scrub radius. Taller tires move you toward negative. So one could do some math, put on taller tires and different offset wheels and keep the same scrub radius as stock or close to it.

Too much negative scrub radius, it’s unstable and provides less feedback.

Bingo! I found a guy who measured!
This is his quote -

A stock Jeep JK Unlimited Rubicon scrub radius is approximately positive 1-1.5-inch with 32” tires.

The problem is that he states taller tires would increase it - looks to me that raising that axle by using taller tires brings the intersection up and reduces scrub radius - am I thinking that right?

One thing that can happen with messing with these angles is the changing of the effect of the SAI - the vehicle may not want to return to center as well. People blame "oh, you don't have enough caster". So they keep bumping caster to compensate when what they've done is made other changes that also impact how the vehicle wants to return to center or track.



Ugh, my head is spinning with math and geometry and I've got powdercoating to do so likely will try to purge this from my head for a while.

The one near the front above the tie rod, with the twirler on it.

BTW - that's a technical term in Virginia.
In Iowa, it's "that turny thing" as my wife would say.

 

[Lunentucker]

I was in three other conversations. LOL
Talk about spinning heads. ??‍

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