Ref.: MEL-WA(3D HCV) - OM Ver.1.7
17
5.5.
THRUST ANGLE
LCV
HCV
Fig. 9
THRUST ANGLE
is the line that divides the total angle of the rear wheels. The rear
tyres are not just following the front tyres, they are actually establishing direction of the
vehicle. In doing so, a direction of thrust is developed. The Thrust angle created by the
rear wheels is used as a reference for aligning the front wheels. Ideally, the Thrust
angle should be identical to the geometric centerline of the vehicle. If Thrust angle and
geometric centerline are identical, the position of the tires would then form an absolute
rectangle and the front tyres could be aligned to the rear tyres, resulting in a perfectly
centered steering wheel. Because of unitized construction, factory tolerances and a
varying degree of damage and / or wear, it is increasingly unlikely that the axles will be
parallel. When the rear axle projects a different angle than the front axle, the driver will
need to turn the steering wheel to compensate in order to drive in a straight line.
On situations where the thrust line and geometric centerline are not identical, a
thorough inspection of the rear axle and suspension system must be done. Replacing
defective components should aid in positioning Thrust angle close to the geometric
centerline. If the Thrust angle is not identical to the geometric centerline and there are
no defective components, align the vehicle using the Thrust angle instead of the
geometric centerline. Aligning the front wheels to the Thrust angle is preferred to
aligning to the geometric centerline. The ability to do this is a significant advantage of
four wheel alignment. The result should be a straight steering wheel as the vehicle
moves straight-ahead.
