WHEELS
AND
TYRES
TOE
OUT
MORE WEAR
ON
R
H.
FRONT
TOE IN
MORE WEAR ON
L.H. FRONT
WHEELS PARALLEL
WEAR EQUAL
c--
CAMBER
DOWN
Fig.
13
Exaggerated Diagram showing effect of
road camber on a car's progress.
As a result the car runs crab-wise, dia-
grammatically illustrated in an exaggerated
form in Fig.
13.
The diagram shows why
nearside tyres are very sensitive to too much
toe in and offside tyres to toe out. It also
shows why sharp
"
fins
"
may appear on one
tyre but not on the other and why the
direction of misalignment can be deter-
mined by noting the posinon of the
"
fins."
Severe misalignment produces clear evi-
dence on both tyres.
The front wheels on a moving car should be
parallel. Tyre wear
can
be affected notice-
ably by quite small variations from this
condition. It will be noted from the dia-
gram that even with parallel wheels the car
is still out of line with its direction of move-
ment, but there is less tendency for the
wear to be concentrated on any one tyre.
The near front tyre sometimes persists
in
wearing faster and more unevenly than the
other tyres even when the mechanical con-
dition of the car and tyre maintenance are
satisfactory. The more severe the average
road camber the more marked will this
tendency be. This is an additional reason
for the regular interchanging of tyres.
(a) Precautions when measuring
Wheel Alignment
(i) The car should have come to rest
from a forward movement. This
ensures as far as possible that the
wheels are in their natural running
positions.
(ii)
It is preferable for alignment to be
checked with the car laden.
(iii)
With conventional base-bar tyre
alignment gauges measurements
in front of and behind the wheel
centres should be taken at the
same points on the tyres or rim
flanges. This is achieved by
marking the tyres where the first
reading is taken and moving the
car forwards approximately half
a road wheel revolution before
taking the second reading at the
same points. With the
Dunlop
Optical Gauge two or three read-
ings should be taken with the car
moved forwards to different posi-
tions-180" road wheel
turn
for
two readings and
120"
for three
readings.
An
average figure
should then be calculated.
Wheels and tyres vary laterally
within their manufacturing toler-
ances, or as the result of service,
and alignment figures obtained
without moving the car are un-
reliable.
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