Alignment is not exactly hardcore but nobody seems to have 37s on the non-hardcore list.

Just got my TJ running with 37" MTRs. I read as much as I can on setting the alignment and it sounded like a 1/16" to 1/8" toe in with about 5 degrees of caster was optimal. I started with 1/16" toe in and it wandered all over the place. I took it to 1/8" toe in and the wander got better but still isn't right. I can keep adding toe but but I don't want to eat up the tires if I don't have to. I'm thinking of bumping the caster from 5 degrees to 7 degrees to see if that solves the problem. I was hoping there are people on the list who have played with 37s and can tell me where the sweet spot is? I'm guessing it's a little different for each setup but it's helpful to know what is working for others.

Thanks,
Whit

Alignment is not exactly hardcore but nobody seems to have 37s on the non-hardcore list.

Just got my TJ running with 37" MTRs. I read as much as I can on setting the alignment and it sounded like a 1/16" to 1/8" toe in with about 5 degrees of caster was optimal. I started with 1/16" toe in and it wandered all over the place. I took it to 1/8" toe in and the wander got better but still isn't right. I can keep adding toe but but I don't want to eat up the tires if I don't have to. I'm thinking of bumping the caster from 5 degrees to 7 degrees to see if that solves the problem. I was hoping there are people on the list who have played with 37s and can tell me where the sweet spot is? I'm guessing it's a little different for each setup but it's helpful to know what is working for others.

Thanks,
Whit

How are you measuring your toe-in? If you're doing it off the tires, then you really don't know where it's at. Clamp some 37" long straight edges to the rotors that are being held on with the lugnuts and do it that way.

Like the caster, things change when the diameter increases. What we use as a measurement is supposed to describe the angle the tires should be set at. If a 30 inch tire at the correct angle shows about 1/8" of toe in, then that same number won't work if you move to 37's. You actually wind up with less toe by using the same dimension and you get more wander.

If you want it close, then mark your straight edges at 30" and do your 1/8" dimension with them centered on the hub.

As far as your caster goes, the relationship of the extended line through the kingpin axis and the contact patch of the tire should be maintained if possible.

As your tire diameter increases, that extended line moves forward relative to the contact patch, so you would need to dial out a bit of caster to around 4-5 degrees. 7-8 degrees is the stock setting on a TJ with the front 30 or 44 and around a 30" tire.

I think I have the toe dialed in. If you mark a spot on the tires, measure the separation and then rotate the marks to the other side you can take out any warp in the rim/tire. Then I used the following chart which is pretty simple math:
http://www.bulletproofsteering.com/img324.gif.

I also measured it off of the rim which and adjusted for the 17" rim as aposed to the 15" that is used as the base.

As far as caster, I'm not sure why the important thing is how far the extended line is in front of the tire centerline. I would think the angle is still the key measurement. If I think of a bicycle with 10 foot forks, I would not want the tire to be 3" in front of the centerline like the 2 foot forks, I think I would want it on the same angle as the original forks. I could be way wrong on this but my theory is that there are many things in play when you go from a 30" tire to a 37" tire and the net result has been that people have had better results with less caster. Heck the old Scouts had zero caster for no specific reason. I'd like to see some real math on this but all I've found is as weak as my bike analogy.

Thanks,
Whit

Tire size and caster will also effect Scrub Radius and Trail. The other thing is worn out/loose parts. I'd be looking to make sure everthing is tight before playing with caster. toe in should be 1/16 - 3/16 from the front of the tire half way up to the rear of the tire half way up (less on the front).

With a bigger tire, you'll need more caster. The tow sounds about right, if the numbers are indeed correct. Keep in mind a 37" tire will flex from the rim to the tread well over 10* so don't be too attached to those measurements.

I run my 37's at 8* of caster and the GPW tracks pretty well down a road. Tow-in was about 1/8" as well.

I run my 37's at 8* of caster and the GPW tracks pretty well down a road. Tow-in was about 1/8" as well.

Of course it tracks well. You have the knuckles leaned back and it has no choice but to go straight ahead. Typically the downside to that is heavier steering.

As you lean the knuckles back, you are forcing the tires towards each other with more force that has to be overcome to steer plus you exacerbate camber change throughout the range of the knuckles motion.

Take it to the extreme to get a better illustration. If your kingpins were parallel to the ground, a whole bunch of vehicle weight would be trying to push the tires towards each other. If they were straight up and down, no vehicle weight would be trying to push them together.