Chevrolet 70 1969 Series, Shop Manual

Page: 491 / 913

WHEELS A N D TIRES 10-4
vehicle, the front tires should be moved to the rear
when 1/5 of the tread life has been used. Match
tires as previously described under "Selection of
Tires."
WHEEL A N D TIRE BALAN CING
It is desirable from the standpoints of tire
wear and vehicle handling ease to maintain proper
balance of front wheel and tire assemblies on all
models. All wheels intended for use on front of
vehicle, such as those switched during periodic
tire rotation and those installed as new or repaired
replacement equipment, should be accurately bal­
anced. This may be accomplished by either of two
types of balancing systems in current use which
balance wheels either on the vehicle or off. The
"On-The-Vehicle" type, however, is the more de­
sirable in that all rolling components (brake drums,
bearings, seals, etc.) are included in the balancing
procedure and thereby have any existing unbalance
corrected.
Wheel balance is the equal distribution of the
weight of the wheel and tire assembly around the
axis of rotation. There are two ways in which
wheels can be balanced - statically and dynamic­
ally; wheels must be statically balanced before
they can be balanced dynamically.
STATIC B A LA N C E
Static balance (sometimes called still balance)
is the equal distribution of weight of the wheel and
tire assembly about the axis of rotation in such a
manner that the assembly has no tendency to ro­
tate by itself, regardless of its position. For ex­
ample: A wheel with a chunk of dirt on the rim will
always rotate by itself until the heavy side is at
the bottom. Any wheel with a heavy side like this
is statically out of balance. Static unbalance of a
wheel causes a hopping or pounding action (up and
down) which frequently leads to wheel "flutter" and
quite often to wheel "tramp."
D Y N A M IC B A L A N C E
Dynamic balance (sometimes called running
balance) means that the wheel must be in static
balance, and also run smoothly at all speeds on an
axis which runs through the centerline of the wheel
and tire and is perpendicular to the axis of rotation.
To insure successful, accurate balancing, the
following precautions must be observed:
Wheel and tire must be clean and free from
all foreign matter. The tires should be in good
condition and properly mounted with the balance
mark on the tire, if any, lined up with the valve.
Bent wheels that have runout over 3 /3 2 " should
either be replaced or straightened before being
balanced.
NOTE
Inspect tire and wheel assembly to determine
if an eccentric or out-of-round condition exists.
Note that this condition, if severe, cannot be "bal­
anced out." An assembly which has an out-of-round
condition exceeding 5/1 6" on 8.25:20 tires and up,
is not suitable for use on the front of the vehicle.
Its use on the rear should be governed by its gen­
eral condition and whether the roundness defect
seriously detracts from overall ride quality.
When balancing wheels and tires, it is rec­
ommended that the instructions covering the oper­
ation of the wheel balancer being used be closely
followed.
SYNTHETIC TUBES
When installing synthetic tubes, coat both
sides of the flap (if used), inner diameter of tube,
and inside of tire beads with a solution of neutral
vegetable oil soap. Use a brush or cloth swab to
apply. Do not allow solution to run down into tire.
This treatment aids tube in shaping itself properly
during inflation. When tube and flap are not prop­
erly lubricated, tube will be stretched thin in the
tire bead and rim regions.
TIRE M O U N T IN G
Tires may be secured on rims by a one-piece
split lock ring, or by a continuous side ring held in
place by a split lock ring. Conventional methods are
used to mount and dismount tires.
IM P O R T A N T : Most truck "rim accidents" are
caused by carelessless and thoughtlessness when
inflating the tire after mounting. Such accidents
are always serious and sometimes fatal. Be on the
safe side -- always follow the precautions explain­
ed below:
On all rims, the lock ring must be fully seated
in the rim gutter before inflating tire. This is im­
portant for the safety of the person inflating the
tire. As a safety measure, observe the following
precautions:
On Budd type wheels, use a steel bar approx­
imately 1" in diameter and long enough to extend
several inches over the lock ring at both ends.
Bend bar so it can be inserted through wheel spoke
openings with both ends of bar extending over the
lock ring. Leave bar in place until tire is fully in­
flated, examine lock ring to see that it is fully
seated, then remove safety bar.
CHEVROLET SERIES 70-80 HEAVY DUTY TRUCK SH O P MANUAL