Figure 12-2.Caster angle.
of excessive positive camber tries to pivot the wheels
out on a vehicle.
2. CASTER ANGLE. When viewed from the side
of the wheel, the caster angle is the degree to which the
kingpin or ball joint tilts forward or rearward in relation
to the frame (fig. 12-2). Like the camber angle, the caster
angle is also measured in degrees. It is shown by a line
drawn straight up and down, as in figure 12-2, and then
a second line drawn through the center of the kingpin or
pivot points. The caster angle is the angle formed at the
point where the two lines cross, as viewed from the side
of the vehicle.
A good example of caster is a bicycle. The fork is
tilted backward at the top. A straight line drawn down
through the front-wheel pivot or kingpin would strike
the ground ahead of the point where the tire contacts the
road. A wheel mounted in this fashion is said to have
positive (+) caster or just caster. If the top of the
kingpin is tilted forward so that a straight line drawn
through it hits behind the point where the tire contacts
the ground, the wheel is said to have negative () caster.
On a vehicle with axle suspension, caster is obtained
by the axle being mounted so that the top of the steering
knuckle or kingpin is tilted to the rear. On a vehicle with