Chevrolet CHEVY VAN G10 SERIES Service Manual page 293

Side Wear—This m ay be caused by incorrect wheel camber,
underinflation, high cam bered roads or by taking corners at
too high a rate o f speed.
T he first tw o causes are the m ost com m on. Cam ber wear
can be readily identified because it occurs only on one side of
the treads, w hereas underinflation causes wear on b o th sides.
Cam ber wear requires correction o f the cam ber first and then
interchanging tires.
T here is, o f course, no correction for high cam bered roads.
Cornering wear is discussed further on.
Misalignment Wear— This is wear due to excessive toe-in or
toe-out. In either case, tires will revolve w ith a side m otion and
scrape the tread rubb er off. If m isalignm ent is severe, the
rubber will be scraped o ff o f b o th tires; if slight, only one will
be affected.
The scraping action against the face o f the tire causes a
small feather edge o f rubber to appear on one side o f the tread
and this feather edge is certain indication o f m isalignm ent. The
rem edy is readjusting toe-in, or rechecking th e entire fro n t end
alignm ent if necessary.
U neven W ear— U neven or sp o tty wear is due to such irregu-
ularities as unequal caster or cam ber, b en t front suspension
parts, out-of-balance wheels, brake drum s o u t o f round, brakes
out o f adjustm ent or other m echanical conditions. The rem edy
in each case consists o f locating the mechanical defect and
correcting it.
Cornering Wear— When a tru ck makes an extrem ely fast
turn, th e w eight is shifted from an even loading on all wheels
to an abnorm al load on the tires on the outside o f the curve
and a very light load on the inside tires, due to centrifugal
force. This unequal loading m ay have tw o unfavorable results.
F irst, th e rear tire on the inside o f the curve m ay be relieved
o f so m uch load th a t it is no longer geared to the road and it
slips, grinding o ff the tread on the inside h a lf o f th e tire at the
excessive rate. This ty p e o f tire shows m uch the same
appearance o f tread wear as tire wear caused by negative
cam ber.
Second, the transfer o f w eight may also overload the
outside tires so m uch th at th ey are laterally distorted resulting
in excessive wear on the outside h alf o f the tire, producing a
type o f wear like th a t caused by excessive positive cam ber.
Cornering wear can be m ost easily distinguished from
abnorm al cam ber wear by the rounding o f the outside
shoulder or edge o f th e tire and by the roughening o f the tread
surface w hich denotes abrasion.
Cornering wear o ften produces a fin or raised p o rtion along
the inside edge o f each row in the tread p attern . In some cases
this fin is alm ost as pronou nced as a toe-in fin, and in others, it
tapers in to a row o f tread blocks to such an exten t th a t the
tire has a definite " step w ear" appearance.
The only rem edy for cornering w ear is proper instruction of
operators. Driving more slowly on curves and turns will avoid
grinding rubber o ff tires. T o offset norm al cornering wear as
m uch as possible, tires should be interchanged at regular
intervals.
Wheel and Tire Balancing
It is desirable from th e standpoints o f tire wear and vehicle
handling ease to m aintain proper balance o f fro n t w heel and
tire assemblies on all models. All wheels intended for use on
fro n t o f vehicle, such as those sw itched during periodic tire
ro ta tio n and those installed as new or repaired replacem ent
equipm ent should be accurately balanced. This may be
accom plished by either o f th e tw o types o f balancing systems
in current use w hich balance wheels either on th e vehicle or
off. The " on th e vehicle" ty p e, however, is th e m ore desirable
in th a t all rolling com ponents (brake drum s, bearings, seals,
etc.) are included in th e balancing procedure and thereby have
any existing unbalance corrected.
Truck Wheel Balance Weights
All 1972 tru ck wells equipped w ith a tubular side ring
(rolled flange rim) on the o u tbo ard side o f the wheel rims
require special design weights to fit. D ynam ic balancing can be
accom plished through use o f these special balance weights
w hich are designed only for installations on the o utb oard side
o f these wheels. Conventional weights fit only the inboard side
o f these wheels.
Static Balance
Static balance (som etim es called still balance) is the equal
distribution o f w eight o f the wheel and tire assembly about
the axis o f ro tatio n in such a m anner that th e assembly has no
tendency to ro tate by itself, regardless o f its position. For
exam ple: A wheel w ith a chunk o f dirt on th e rim will always
rotate by itself until the heavy side is at the b o tto m . Any
wheel w ith a heavy side like this is statically o u t o f balance.
Static unbalance o f a wheel causes a hopping or pounding
action (up and dow n) w hich frequently leads to wheel
" flu tte r" and quite o fte n to w heel " tram p " .
Dynamic Balance
D ynam ic balance (som etim es called running balance) means
th at the w heel m ust be in static balance, and also run
sm oothly at all speeds.
To insure successful, accurate balancing, the following
precautions m ust be observed:
• Wheel and tire m ust be clean and free from all foreign
m atter.
• The tires should be in good condition and properly
m ounted w ith th e balance m ark on th e tire, if any, lined
up w ith th e valve.
• ,Bent wheels th a t have ru n o u t over 1 /1 6 " on 1 /2 , 3 /4 and
1
to n trucks should either be replaced or straightened
before being balanced.
• Inspect tire and wheel assembly to determ ine if an
eccentric or out-of-round condition exists. N ote th a t this
co ndition, if severe, cannot be " balanced o u t" . An
assembly w hich has an out-of-round condition exceeding
3 /1 6 " is n o t suitable for use on the fro n t o f th e vehicle.
Its use on the rear should be governed by its general
condition and w hether the roundness defect seriously
detracts from th e overall ride quality.
• When balancing wheels and tires, it is recom m ended th at
th e instructions covering the operation o f the wheel
balancer being used be closely follow ed.
WHEELS A N D TIRES 10-3
C H E V Y V A N SH O P M A N U A L