Castor is the angle produced between the line running through
the steering axis (2) in the direction of the axis of symmetry and
a vertical line (1) through the wheel centre to the road.
The castor is negative if the point of intersection of this
imaginary line with the plane of the road is behind the wheel
contact point. It is positive if it is in front of the wheel
contact point.
A positively adjusted castor pulls the wheels which helps to
restore the wheels to the straight-ahead position after
cornering.
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