Originally Posted by jeepdaddy2000
Gonna plagiarize a bit here:
Too much caster and too much toe-in can induce death wobble. Too little caster and too much toe-out can cause wandering. Identify your symptom. If the tires start oscillating and hopping violently, you've got death wobble. Increasing the toe setting to as much as 3/8-inch toe-out (yes, readers toe-out; no misprint) has been known to help, or if possible, dialing the caster back to 3-4 degrees positive (bottom ball joint in front of top). The larger your tires, the less caster you should need.
A good example of this is a shopping cart. we have all seen the wheels wobble like a leaf in the wind. If you imagine a line from the mounting point through the axle, you will see probably the most extreme positive caster out there.
This problem is very common with coil sprung vehicles such as Bronco's, where lifting it means rotating the front axle forward. Early Bronc's used poly replacement bushings in 2, 4, and 6 degrees to counter this.
There a a couple of forces that add to wheel centering effect. One is from the tire tread (pneumatic trail) which induces the tire to travel in a straight line. It is based on the tread type, tread-block flexibility, and tire width. The other is positive caster (mechanical trail).
Excessive toe adjustment is the culprit, not too much positive caster. The scrubbing force will cause the tire to hop. It could wobble but would most likely hop.
In the shopping cart example, the damaged wheel wobbles because it no longer makes constant contact. It is flipped back and forth when it touches the ground on each side of the steering axis and encounters the centering force (mechanical trail). It actually has less "caster" because the "steering" axis it angled back toward the rotational axis (this also lets the wheel break contact with the ground when it approaches the center). If it maintained constant contact, the wheel would just straighten out.
As for toe out... Wheels are toe'd in because during normal operation the wheels are forced outward slightly, in-effect straightening out.
Regarding larger tires... they will amplify your caster effect (good or bad).
There are many more things I didn't cover here... need to update my article. Like I said earlier. Always ready to learn more. Thanks.