Paper - II Auto Chassis and Body Engineering 103
Fig 2.9 Ackerman steering gear
2.7 Steering geometry - Caster, Camber, Kingpin inclination,
toe-in and toe-out.
Steering Geometry : It refers to the positioning of the front wheels
and steering mechanism that gives the vehicle directional stability , promotes
ease of steering and reduces tyre wear to a minimum. It also refers to the angular
relationship between the front wheels and parts attached to the front wheel,
frame of the vehicle. It depends upon the following terms. Caster angle, camber
angle, King Pin inclination , Toe-in Toe-Out on turn.
Caster angle: It is the angle of tilting the king pin axis either forward or
backward from the vertical line. This tilting is known as Caster. The angle between
the vertical line and the king pin centre line in the plane of the wheel (When
viewed from the side) is called the Caster angle.
Center of contact is di- Swivel line(steering axis) con-
rectly under spindle tacts ground plane ahead of
contact patch
Fig 2.10 Caster angle
104 Automobile Engineering Technician
When the top of the king pin is backward, the caster angle is positive,
and when it is forward, the caster angle is negative. Usually the caster angle in
modern vehicles ranges from 2 to 8 degrees.
The main purpose of caster angle is to create self centering effect in the
steering. It provides the directional stability. It positive caster increase the efforts
required to steer and tries to keep the wheels straight ahead. In heavy duty
trucks negative caster is preferred. This makes the steering easier.
Camber Angle : It is the angle between the centre line of the tyre and
the vertical. When viewed from the front of the vehicle when the angle is outward,
so that the wheels are farther apart at the top the camber is “Positive” when the
angle is inward, so that the wheels are closer together at the top, the camber is
“Negative”. The usual value of camber angle should not exceed 2o.
When the camber angle is positive, it causes slip out prevention lightens
the perpendicular load and lessen the required steering effort. If it is a Zero
camber, it prevents uneven wear of tyres. When the camber angle is negative,
the camber thrust increase with increase in tyre inclination relative to the road
surface.
- Negative + Positive
CAMBER
Fig 2.11 Camber angle
Paper - II Auto Chassis and Body Engineering 105
King Pin Inclination or steering Axis Inclination
It is the angle between the vertical line and the center of the King pin the
steering axis when viewed from the front. The Kingpin inclination, in combination
with caster angle, is used to provide directional stability . It also reduces steering
effort particularly when the vehicle is stationary. It reduces tyre wear also. The
kingpin inclination in modern vehicle ranges from 4o to 8o. It is also known as
steering Axis inclination.
Fig 2.12 King pin inclination
Toe-In : It is the inward tilting of front wheels at the front so that the
distance between the front wheels at the front is less than the distance between
at the front wheels at the rear when viewed from the top. The Amount of the
Toe-in is usually 3 to 5 mm .
Fig 2.13Toe-in
106 Automobile Engineering Technician
The toe-in is provided to ensure parallel rolling of the front wheels to
stabilize steering and prevent side slipping of front wheels and thereby prevent
excessive tyre wear.
Toe-Out : Toe-out is the differenence in angles between the two front
wheels and the car frame during turns. The steering system is designed to the
turn the inside wheel through a larger angle than the outside wheel when making
a turn. The toe-out is secured by providing the proper relationship between
steering knuckle arms, tie rods and pitman arm (drop arm).
Fig 2.14 Toe-out
2.8 Steering defects - Wheel Wobble and Shimmy
(i) Wheel wobble and shimmy : when the vehicle go through an uneven
or rough road, the front wheel will get shaken for a while. This problem can also
be seen when the vehicle is slowing down. This problem may caused by the
following reason.
Reason Remedy
1. Unbalanced wheels 1. The wheels should be balanced at
wheel balance
2. Unevenly worn out tyres 2 . Rotate the tyres or Replace with
new ones if necessary
3. Inoperative shock absorbers 3. Replace them
4. Incorrect Toe-in 4. Adjust the Toe-in
5. Loose spring U-Bolts 5. Tighten
6. Loose steering linkages 6. Tighten
7. Worn out kingpin steering , 7. Tighten or Replace as per
linkages the necessity wheel bearings,
steering gear
8. Inoperative stabilizer 8. Replace
ACKERMarSteERNG MECHlisN
BL4t Tun
BauhAr
Gko
UND
NEGATINE NEUTRAL PosITiNG
CAMBER CAMBER CANBER
VEHCLE
VENIKLE
VEHK
feorT Ront FRon
RosITNE NEUT2AL
NeGATINE
CASTEK CASTER ASTEK
ToE-TN ToE-DuT
T Y R E C E N T R E
L I N E
CnMBCEaC
MBER
NGLE
-N6RTICA LINE
KMG PIN
LNCLINATION
KiwG-PIN NNaToN
