Trail or Trailing
The steering axis (the red dotted line in the diagram above) does not have to pass through the center of the wheel, so the caster can be set independently of the mechanical trail, which is the distance between where the steering axis hits the ground, in side view, and the point directly below the axle. The interaction between caster angle and trail is complex, but roughly speaking they both aid steering, caster tends to add damping, while trail adds 'feel', and returnability. In the extreme case of the shopping trolley wheel, the system is undamped but stable, as the wheel oscillates around the 'correct' path. The shopping trolley/cart setup has a great deal of trail, but no caster. Complicating this still further is that the lateral forces at the tire do not act at the center of the contact patch, but at a distance behind the nominal contact patch. This distance is called the pneumatic trail and varies with speed, load, steer angle, surface, tire type, tire pressure and time. A good starting point for this is 30 mm behind the nominal contact patch.
Read more about this topic: Caster Angle
Famous quotes containing the words trail and/or trailing:
“Perhaps of all our untamed quadrupeds, the fox has obtained the widest and most familiar reputation.... His recent tracks still give variety to a winter’s walk. I tread in the steps of the fox that has gone before me by some hours, or which perhaps I have started, with such a tip-toe of expectation as if I were on the trail of the Spirit itself which resides in the wood, and expected soon to catch it in its lair.”
—Henry David Thoreau (1817–1862)
“As I came home through the woods with my string of fish, trailing my pole, it being now quite dark, I caught a glimpse of a woodchuck stealing across my path, and felt a strange thrill of savage delight, and was strongly tempted to seize and devour him raw; not that I was hungry then, except for that wildness which he represented.”
—Henry David Thoreau (1817–1862)