WHEELS
AND
'IYRES
worn at irregular spacings round the
circumference-indicates an alternat-
ing
"
slip-grip
"
phenomenon but it is
seldom possible to associate its origin
and development with any single
cause.
It is preferable to check all points
which may be contributory factors.
The front tyre and wheel assemblies
Fig.
12
Fins and Feathers
due
to
severe mis-
alignment.
may then be interchanged, which
will
also reverse their direction of rotation,
or better still the front tyres may be
interchanged with the rear tyres.
Points for checking are
:-
Inflation pre&res and the con-
sistency with which the pressures
are maintained.
Brake freedom and balance, shoe
settings, lining condition,
drum
condition and truth.
Wheel alignment.
Camber and similarity of camber
of the front wheels.
Play
in
hub bearings, king pin
bearings, suspension bearings and
steering joints.
(f)
Wheel concentricity at the tyre
bead seats.
S.M.M.
&
T.
toler-
ances provide for a radial throw
not exceeding
$",
but this may be
affected by impact or other
damage.
(g)
Balance of wheel and tyre assem-
blies.
(h) Condition of road springs and
shock absorbers.
Corrections which may follow a check
of these points will not always effect a
complete cure and it may be necessary
to continue to interchange wheel posi-
tions and reverse directions of rotation
at suitable intervals.
Irregular wear may be inherent in the
local road conditions such as from a
combination of steep camber, abrasive
surfaces, and frequent hills and bends.
Driving methods may also be involved.
Irregular wear is likely to be more
prevalent in summer than in winter,
particularly on new or little worn tyres.
3.
WHEEL
ALIGNMENT
AND
ITS
ASSOCIATION
WITH
ROAD
CAM-
BER
It is very important that
correct
wheel
alignment should be maintained. Mis-
alignment causes a tyre tread to be scrubbed
off laterally because the natural direction of
the wheel differs from that of the car.
An
upstanding sharp
"
fin
"
on the edge of
each pattern rib is a sure sign of misalign-
ment and it is ssible to determine from
the position o
P"
the "fins" whether the
wheels are toed in or toed out (Fig.
12).
"
Fins
"
on the inside edges of the pattern
ribs--nearest to the car-and particularly
on the nearside tyre indicate toe in. "Fins"
on the outside edges, particularly on the
offside
tyre, indicate toe out.
With minor misalignment the evidence is
less noticeable and sharp pattern edges may
be caused by road camber even when wheel
alignment is correct. In such cases it is
better to make sure by checking with
an
alignment gauge.
Road camber affects the directionof the
car
by
imposing a side thrust and
if
left to follow
its natural course the car will drift towards
the nearside. This is instinctively corrected
by steering towards the road centre.
To Next Page
Loading...
