Specifications

Alignment & Adjustments 38 17730-248
AIRTEK
®
•
SOFTEK
®
for Blue Bird Buses
SECTION 8
Alignment & Adjustments
ALIGNMENT DEFINITIONS
FIGURE 8-1
Ackermann Steering Geometry —
The geometry of the four bar linkage
consisting of the front axle beam
pivot points, tie rod arms, and cross
tube and attempts to provide free
rolling of front tires in a turn.
Ackermann geometry is dependent
upon the steering axle track-width
and wheelbase of the vehicle.
Improper geometry results in wheel
scrub in turns which generally
appears as toe wear on the tire.
Usually more wear is present on one
side of the vehicle than the other due to the operational route of the vehicle.
Bump Steer (Feedback) — The feedback felt through the steering linkage to the steering
wheel when a steer axle tire hits a bump in the road. This occurs because the axle-end of
the drag link and the axle attachment point of the spring do not travel in parallel circular
arcs as the suspension moves up and down. This condition can also be caused by trapped
air in the power steering system.
FIGURE 8-2
Camber — The angle formed by the inward or outward tilt of the
wheel reference to a vertical line. Camber is positive when the
wheel is tilted outward at the top and is negative when the wheel is
tilted inward at the top.
Excessive positive camber may cause smooth wear on the outer half
of the tire tread. Excessive negative camber may cause wear on the
inner half of the tread. Static-unloaded camber angles are built into
the axle to put the loaded tire perpendicular to the road.
FIGURE 8-3
Caster — The forward or rearward
tilt of the steering axle kingpin in
reference to a vertical line. The
angle is measured in degrees.
Caster is positive when the top of
the steering axis is titled rearward
and is negative when the tilt is for-
ward. Proper caster is important
for directional stability and return-
ability. Too much positive caster
can cause shimmy, excessive
steering effort and is normally a vehicle performance and handling consideration. Uneven
positive caster may create a steering pull toward the side with the lower caster. This attrib-
ute may be used to compensate for crowned roads.
ACKERMANN GEOMETRY
Center of Rotation
Rear Axle
Wheel
Base
L
80
1
APPENDIX
SERVICE MANUAL