GMC 4000 Series Service Manual page 520

on all trucks should receive the same amount of
careful system atic, and regular maintenance as
do other operating units. The three major causes
of tire troubles are (1) underinflation (2) bruises
and (3) misalignment. T ires should be checked
periodically to prevent excessive damage caused
by these conditions.
Periodically check the valve stem cores and
caps for leakage. Also, check around tires for
embedded steel, rock, or glass. If any of these
objects are allowed to remain in tread, they may
eventually reach the tube.
NOTE: In some instances the tube of an in­
flated tire may already be punctured and pressure
w ill be lost only when object is removed.
INFLATION OF TIRES
Under-inflation is the greatest cause for loss
of tire life expectancy. T ires should be checked
frequently for this condition. The fabric, rubber,
bead, contour, and size of tires used on these ve­
hicles are designed to obtain maximum length of
service under all operating conditions to which
vehicles may be subjected. TIRES ARE DESIGNED
TO OPERATE EFFICIENTLY ONLY ON A PRE­
SCRIBED AMOUNT OF AIR. Unless the correct air
pressure is consistently maintained, the tires will
not function as they should; consequently, safe
economical operation of vehicle will be materially
affected.
An under-inflated tire runs sluggishly, heats
up quickly because of the greater flexing, and is
subjected to more frequent bruising. In the situation
of duals, lo ss of pressure in one tire could cause
slippage of rim on wheel with the result of tire,
tube, rim and spacer lo ss. On the other hand, over­
inflation may weaken the tire, causing a blow-out.
In addition to the deteriorating effect improperly
inflated tires may have on the tire life, this con­
dition will affect steering, riding comfort, and safe
driving. FOLLOW THE TIRE PRESSURE RECOM­
MENDATIONS OF THE TIRE MANUFACTURER.
For greater riding comfort, prolonged tire
life, and to reduce wear and tear on the truck
ch assis, tires should be inflated for loads carried
on tires as indicated in "Tire Load and Inflation
Table" in "Specifications" at end of this section.
In no case should this combined front and rear
tire load exceed the maximum recommended load
shown in "Load Capacity Chart" in the current
Owner's and Driver's Manual.
BALANCED INFLATION
The whole efficiency of the vehicle will be up­
set if air pressure in the tires are out-of-balance.
Balanced inflation may be expressed as: All tires
on the same axle should always carry the same
G M C S E R V I C E M A N U A L
air pressure. A difference in air pressure of the
rear tires and the front tires may be perm issible
within certain limitations; however, there should
not be a difference in p ressures between the right
and left tires on the same axle. A five-pound under­
inflation in one front tire not only can destroy ease
of steering, but creates steering hazards which
generally point to a potential accident. An under­
inflated rear tire can destroy the value of the most
efficient brakes. Balance tires for ease of steering,
comfort in riding, safety in driving, as well as for
minimum fuel consumption and maximum tire m ile­
age.
PRESSURE LOSS
gauged for pressure lo ss with an accurate gauge
before tires are brought to correct operating p res­
sure. The purpose of this check is to determine
the exact pressure lo ss in each tire. In other
words, if at the time this check is made, a definite
p ressure lo ss is noted in any one of the tires, an
WHEELS A N D TIRES
Figure 4 — M ethod of Checking for Distorted W heels
At periodic intervals, each tire should be
Figure 5 — Typical W hee l C h e ck in g D iag ram
Sec. 10
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