Audatex 2012
Certification
Steering Geometry
Module
Pre-course reading
Understanding the basic angles
• Toe angle
• Camber angle
• Castor angle
• King Pin Inclination/Steering Axis Inclination
• Included angle
• Thrust angle/thrust line
• Ackermann angle/toe out on turns
Toe angle – wheel alignment
• The angle of the road
wheels compared to the
centre line of the
vehicle
• Set ‘in’ or ‘out’ as
driving forces change
angles of wheels when
in motion (R.W.D. move
out – F.W.D. move in)
• Wheels parallel when
vehicle in motion
• Measured for front and
rear wheels
Camber angle
•
The angle of the centre
line of the wheel
compared to the true
vertical (90° from the
ground)
•
Positive camber – makes
steering lighter – tends to
make vehicles understeer
•
Negative camber – aides
handling as there is less
tyre ‘roll’
•
Measured for front and
rear wheels
Castor angle
• The angle of swivel/strut
compared to the vertical
viewed from the side
• Give self-centering after
corners
• Makes vehicles more stable
• Most vehicles have positive
castor (swivel leaning back as
in image)
• Measured for front wheels
only
King Pin/Steering Axis Inclination
– K.P.I/S.A.I.
•
Is the angle of swivel
point/king pin compared to
the vertical line
•
Aides self centering
Included angle
•
The angle between the centre
line of the swivel (K.P.I./S.A.I.)
and the centre line of the wheel
•
Is there for measurement
purposes only
•
Included angle = K.P.I/S.A.I +
Camber angle
Thrust angle/axis
• The angle between the
theoretical centre line of the
vehicle (90° from rear axle
line) and the actual centre line
of the vehicle
• Incorrect thrust axis causes
‘crabbing’
• Measured from the rear
wheels
Ackermann steering angle
• The angle between the
right angles (90°) of the
front wheels and a
theoretical point at the
centre of the ‘turning
circle’
• Allows the front wheels
to go through different
angles to aide cornering
and reduce tyre wear
Ackermann steering principle – toe out on turns
Parallel steering arms
No ‘Ackermann Effect’ as
wheels turns through same
angle
Angled steering arms
‘Ackermann Effect’ as angled
arms mean wheels turn
through different angles
Geometry checks – minimum requirements
• Correct tyre pressures
• Level ground
• All fluid levels correct
• Fuel tank full (or weighted accordingly) or correct
ride height
• No damage to suspension or steering
• No signs of wear to suspension or steering