TRUCK SERVICE MANUAL
WHEELS, RIMS, TIRES
and bounce at high speed rotation because of its being
alignment. See "TORQUE CHART" for correct torque
values.
out of balance dynamically.
After rim has been properly torqued, it should be
Dynamic Balancing
checked for alignment. This can be accomplished by
rotating wheel with a piece of chalk attached to a steady,
Dynamic balancing is complete wheel balancing
firm surface and placed to just barely clear outside
of which static balancing is only a part.
surface of tire bead seat. This procedure will point out the
Dynamic balancing (in motion) takes into
"high spot". Keep in mind, however, that a "high spot"
consideration the distribution of weight to be added to the
does not necessarily mean that lug nuts have been
wheel. This is accomplished by rapidly rotating (normal
unevenly tightened. This condition or misalignment can
truck operating speed) the wheel and tire assembly either
also result from a bent wheel.
on the vehicle or with the wheel assembly removed and
placed on a dynamic balancing machine. This
WHEEL AND TIRE BALANCING
determines heavy point on wheel.
When the amount of weight required to offset a
Front wheel and tire assemblies must be
heavy part in a wheel assembly is known, it is sometimes
balanced to prevent wheel vibrating and bounce. While
necessary to attach one-half of the weight to the outside
the correct front wheel alignment is necessary for easy
rim flange and the remaining half to the inside rim flange.
steering and maximum tire life, the cause of unstable
With the weight properly distributed on the wheel
steering can be frequently traced to improper balance of
assembly, the wheel should be in balance both statically
front wheels. When this condition exists, the wheel
and dynamically and should rotate free of vibration and
bounce at normal truck operating speeds.
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
TIRE CARE
cannot be corrected by balancing. In such cases the tire
should be replaced before attempting to balance the
Proper tire inflation, tire loads, and road speeds
assembly.
are important determining factors governing tire mileage,
and also affect steering ease and maneuverability. How
Static Balancing
much these three factors affect tire wear is illustrated in
the paragraphs which follow.
A wheel out of balance statically has a tendency
to bounce up and down resulting in rapid tire wear in
INFLATION
round or oblong spots.
Static balancing is performed while wheel is
Tire pressures should be checked at regular and
stationary by attaching weights to rim flange to offset an
frequent intervals and the pressures maintained to
opposite heavy point.
specifications. Use an accurate tire pressure gauge and
Static balancing may be sufficient in some
check when tires are cool. The chart (Fig. 10) illustrates
instances where vehicle is operated only at slow speeds,
the loss in tire mileage caused by underinflation. It will be
however, dynamic balancing (in motion) balances the
noted that a tire underinflated only 20% will produce only
wheel and tire assembly statically as well as dynamically,
70% normal mileage.
thereby eliminating vibrations and wheel bounce at both
low and high speeds. NOTE: A wheel may be perfectly
balanced statically (not in motion) but may still vibrate
Fig. 10 Inflation vs. Mileage
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