Spicer Steer Axles Application Guidelines - Manual (Page 42)

< 36 > back AXAG400 – February 2007
6- Glossary of Terms
ABS – Antilock Brake System; ABS electronically monitors wheel speed and prevents wheel lock-up by
rapidly cycling the brakes during panic stops and when stopping on low-friction surfaces.
Ackermann geometry – the relative angular movements of the front wheels while traveling along a
curved path; a double pivoting steering system where the outer tie rod arms are bent slightly inward
so that when a vehicle is making a turn, the wheels toe-out and the inside wheel will turn more
sharply than the outer wheel; this is done to compensate for the greater distance the outside wheel
must travel; these angular movements relate to the length of wheelbase and the width of track; true
Ackermann geometry includes the Jeantaud modification to Rudolph Ackermann’s original principle.
Alignment – method of maintaining proper relationship between all components of the steering system.
Beam drop – distance from the kingpin to spindle intersection and the spring mounting pad surface.
Bearing shoulder to bearing shoulder dimension – distance from the machined inner bearing contact
point on one side of the axle to the other machined inner bearing contact point on the other side.
Belleville washer – also known as coned-disc springs or Belleville disc springs; provide very high loads
at small deflection and also maintain a constant force regardless of dimensional variations due to
wear, temperature changes or tolerances.
Bridge formula – formula used to determine maximum gross weight permissible on any group of axles.
Broached bushing – bushing that is finished by a round cutting tool that has multiple teeth each
removing a small portion of the bushing material to achieve desired finished size.
Camber – the tilt of the wheel side to side while looking from the front; places the road contact point
closer to the king pin axis thereby reducing road inputs to the steering system and contributes to
steering stability.
Camber, negative – top of the wheel tilts inward.
Camber, positive – top of the wheel tilts outward.
Caster – tilt of the kingpin centerline looking from the side; offers directional stability and assists in
returning wheels to a straight ahead position through self centering action.
Caster, Negative – kingpin centerline projected behind the road contact point.
Caster, Positive – kingpin centerline projected ahead of the road contact point.
Compressible inserts – foam inserts installed in the top and bottom of the kingpin under the cap that
reduce the pressure/vacuum that is found in the bushing area during typical service.
Cramp angle – maximum turn of steering wheel in either direction.
Creep rating – load rating for a vehicle used at a regulated low speed while maneuvering or driving with
lift able axles in retracted mode.
Cross link – composed of the adjustable cross tube and threaded tie rod ends with ball sockets that
connect the LH knuckle tie rod arm to the RH knuckle tie rod arm.
Cross tube – center tube portion of a cross link assembly that is threaded with opposite threads on each
end thereby allowing adjustment by turning the tube with one hand.
CTI – Central Tire Inflation; means of easily adjust the vehicle tire pressure, both inflate and deflate, for
the conditions encountered whereby improving vehicle mobility performance.
Double drop – beam having a drop in the center between the spring mounting pads as well as the drop
from the KPI to the spring mounting pads.
Draglink – connection between the pitman arm and the steer ball on the steer arm; acts as a pull-and-
push rod to convey steering movements from the chassis-mounted steering box to the spring-
mounted axle.
Draw key – fastener that works like a wedge and provides a mechanism to lock the beam to the kingpin
while allowing rotation of the knuckle on the kingpin.
Drop socket – socket with the ball center not coincident with the threaded end.
Dry park maneuver – turning steering wheel/tires without any forward or reverse movement.
Dual draw key – arrangement of two draw keys used to balance load on kingpin maintain alignment of
kingpin to knuckle/beam bore.
Foam insert – foam piece also know as the compressible insert.
GAWR – Gross Axle Weight Rating; is the total weight capacity of the axle.
GCWR – Gross Combination Weight Rating; is the total weight capacity of a combination vehicle, (tractor
and trailer) as determined by axle ratings; it includes the weight of the vehicle and payload.
Grade – the degree of inclination of a road.
I-Beam – forged steel structural beam constructed in the shape of an “I”.
IASS – InterAxle Speed Sensor.