Quote:
Originally Posted by V8COOPMAN
Really? Can you PLEASE explain how that happens? DD
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Sure. With caster being defined as the centerline of the kingpin (in our cars), measured in degrees from true vertical, as viewed from the side, it's the physics of "for every action there is an equal and opposite reaction"..
At zero degrees caster the spindle snout/stub will be parallel to the ground as the spindle is rotated on the kingpin. As caster is increased from zero to a positive angle, the snout is no longer moving parallel to the ground as it rotates, but is pushing down toward the ground as it moves rearward, since the kingpin is tilted. Since it can only move down as far as the tire's compression will allow, it then tries to lift the weight on it.
As the positive caster angle increases, say 3 to 6 degrees, more static steering effort is needed to push the snout down (or lift the weight), as the force and snout is pushing more vertically downward. This steering effort has to come in the form of more muscle, leverage from a larger diameter steering wheel, longer pitman arm, or power assist.
But once moving, the tire's rotation has a gyroscopic effect and as downward force is put toward the ground, the weight being raised wants to return down, the snout returns to neutral, and the steering straightens out. Right or left turn is the same, given equal caster angle on both sides.
Visualize the high caster on a dragster, more force is required to deviate the tire from straight ahead. Which is why a higher caster angle will resist drifting and road walk, but requires more input effort at rest. Of course the dragster has light front weight, and that conversely requires higher caster.
I probably omitted some variables and fine points, but that's it in a big nutshell.