Ref.: MEL-WA(3D HCV) - OM Ver.1.7
15
5.3.
CASTER
CASTER
is the angle between an imaginary line drawn through the upper and lower
steering pivots and a line perpendicular to the road surface (viewed from side of
vehicle). If the top of the line tilts rearward, the vehicle is said to have
POSITIVE
CASTER
.
Fig. 6
If the top of the line tilts forward, the vehicle is said to have
NEGATIVE CASTER
.
Fig. 7
Positive Caster can also be defined as when the spindle is tipped so that the pivot
support centerline intersects the road surface at a point in front of the initial tire contact.
Negative Caster would then be the center line intersection to the road surface behind
the initial tire contact.
Most vehicles produced today do not have adjustable Caster angle. Many early model
vehicles have adjustable Caster in which road crown is compensated for (along with
Camber). By setting the Caster angle on the Driver‟s side 1/2 degree less than the
passenger side for Positive Caster specifications or 1/2 degree more for Negative
Caster specifications, the road crown should not cause vehicle pull in either direction.
Vehicles equipped with manual Steering use very little Positive or Negative Caster.
This helps reduce the Steering effort at the Steering wheel.
The advantage of Caster adjusted toward Negative is greater maneuverability.
however, direction stability on open road driving is reduced. The advantage of Positive
Caster is the strong directional stability and the ease of returning the steering to a
straight ahead position. Caster will not cause tyre wear unless extreme mis-adjustment
or worn parts are involved. Always set Caster (if adjustable) to specifications and
within 1/2 degree from side to side. Keep road crown in mind and adjust as necessary
if a pull is present after a proper alignment has been completed.
