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Caster is referred to the displacement of the angle that the steering axis is offset from the vertical, measured from front to back. It lets the wheel align with the direction of travel.

Caster Alignment

  • If the steering knuckle tilts toward the back, the caster is positive, and if it tilts toward the front, the caster is negative.
  • The tilting of the steering axis forward or backward provides directional steering stability and is aided by a positive caster, while a negative caster makes steering easier.
  • It causes the steering axis to pass through the road surface ahead of the center of tire contact with the road.
  • It places the push on the steering axis ahead of the road resistance to the tire.
  • The tire trails behind, as the positive caster causes the steering axis to lead or pull the tire and wheel down the road. Additionally, it keeps the wheels pointed straight ahead, which helps overcome any tendency for the vehicle to steer away.