WHEELS, RIMS AND TIRES
WHEEL AND TIRE BALANCING
Front wheel and tire assemblies must be balanced to
prevent wheel vibrating and bounce. While the correct
front wheel alignment is necessary for easy steering and
maximum tire life, the cause of unstable steering can
frequently be traced to improper balance of front wheels.
When this condition exists, the wheel and tire assembly
should be properly balanced.
A vulcanized or retreaded tire, or a tire that has a boot in
it, may cause an unbalanced condition that cannot be
corrected by balancing. In such cases the tire should be
replaced before attempting to balance the assembly.
Static Balancing
A wheel out of balance statically has a tendency to
bounce up and down, resulting in rapid tire wear in round
or oblong spots.
Static balancing is performed while wheel is stationary by
attaching weights to rim flange to offset an opposite
heavy point.
Static balancing may be sufficient in some instances
where vehicle is operated only at slow speeds, however,
dynamic balancing (in motion) balances the wheel and
tire assembly statically as well as dynamically, thereby
eliminating vibrations and wheel bounce at both low and
high speeds.
A wheel may be perfectly balanced statically (not in
motion) but may still vibrate and bounce at high speed
rotation because of its being out of balance dynamically.
Dynamic Balancing
Dynamic balancing is complete wheel balancing of which
static balancing is only a part.
Dynamic balancing (in motion) takes into consideration
the distribution of weight to be added to the wheel. This
Is accomplished by rapidly rotating (normal truck
operating speed) the wheel and tire assembly either on
the vehicle or with the wheel assembly removed and
placed on a dynamic balancing machine. This
determines heavy point on wheel.
When the amount of weight required to offset a heavy
part in a wheel assembly is known, it is sometimes
necessary to attach one-half of the weight to the outside
rim flange and the remaining half to the inside rim flange.
With the weight properly distributed on the wheel
assembly, the wheel should be in balance both statically
and dynamically and should rotate free of vibration and
bounce at normal truck operating speeds.
TIRE CARE
Proper tire inflation, tire loads, and road speeds are
important determining factors governing tire mileage,
and also affect steering ease and maneuverability. How
much these three factors affect tire wear is illustrated in
the paragraphs which follow.
INFLATION
Tire pressures should be checked at regular and
frequent intervals and the pressures maintained to
specifications. Use an accurate tire pressure gauge and
check when tires are cool.
Over inflated or under inflated tires will reduce the ser-
vice life of the tire.
"Bleeding" of air from hot tires should never be practiced.
The pressure will be reduced but an increase in
temperature will result as soon as driving continues.
LOADS
Loading tires beyond their rated capacity is expensive
because tire mileages are rapidly decreased with
overloads.
TIRE MATCHING
Dual Tires
Use care in matching dual tires. Tires which differ more
than 6.35 mm (1/4") in diameter or 19.05 mm (3/4") In
circumference should not be mounted on the same dual
wheel. Should it become necessary to mount two tires of
unequal size on the same dual wheel, place the larger or
less worn tire on the outside.
Tandem Drive Axles
When mounting tires on tandem drive axles follow the
same instructions as specified for dual tires. However,
never install the four largest tires on one driving axle and
the four smallest on the other. This method of tire
mounting will cause high lubricant temperatures which
may lead to premature axle failures.
CTS-4148A
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