Pontiac FIREBIRD 1972 Service Manual page 1238

SECTION 10
W H E E L S AND TIRES
The following caution applies to one or more steps in the assembly proce-
dure of components in this portion of the manual as indicated at appropri-
ate locations by the terminology "See Caution on page 1 of this Section".
C AUTI 0 N: THIS FASTENER IS AN IMPOR TA NT A TTA CHING
PART IN THAT IT COULD AFFECT THE PERFORMANCE OF
VITAL COMPONENTS AND SYSTEMS, AND/OR COULD RE-
SULT IN MAJOR REPAIR EXPENSE. IT MUST BE REPLACED
WITH ONE OF THE SAME PART NUMBER OR WITH AN
EQUIVALENT PAR T IF REPLACEMENT BECOMES NECES-
SAR Y. DO NOT USE A REPLACEMENTPAR T OF LESSER QUAL-
ITY OR SUBSTITUTE DESIGN. TORQUE VALUES MUST BE
USED AS SPECIFIED DURING REASSEMBLY TO ASSURE
PROPER RETENTION OF THIS PART.
CONTENTS OF THIS SECTION
Trouble Diagnosis and Service Testing
..................
10-1 Wheel and Tire Balance
..........................................
10-6
..........................................................
General Description
................................................
10-4 Minor Repairs 10-7
Tire Size and Load Range
......................................
10-4 Puncture Repair
......................................................
10-9
..................................................
Inflation of Tires
......................................................
10-4 Balance Procedure 10-9
Tire Rotation
.......................................................
10-5
TROUBLE DIAGNOSIS AND TESTING
TIRE INSPECTION (Fig. 10-1)
It is characteristic of belted bias ply tires to display an
apparent rapid but even wear of the second tread rows
from the outer and inner shoulders. This condition is nor-
mal and does not decrease the tread life of the tire. Tire
rotation at recommended intervals will assist in minimiz-
ing this type of wear (Fig. 10-2). Careful inspection of tires
may show that improper wheel alignment, poorly adjusted
brakes, poor driving habits, fast cornering or other condi-
tions are the cause of wear. Listed below are common
types of irregular tire wear and possible causes.
from being jammed against the rim and crushed or cut
when the tire strikes a curb, rock, or rut.
When a tire is overinflated, increased tension caused by
excessive pressure prevents proper deflection of the side-
walls. This results in wear in the center of the tread and
the tire also loses its ability to absorb road shocks. Under
this increased strain, cords in the belt or sidewall cords
may snap under impact.
UNDERINFLATION
SIDE WEAR (CAMBER OR CORNERING WEAR)
The result of underinflation is shown in Fig. 10-1. Car There are three reasons why tires wear more rapidly on
weight distorts the normal contour of the tire body and the one side of the tread than on the other.
tire bulges out. This wears the tread at the edges more
than the center and generates excessive internal heat, 1. Wheel camber causes the tires to run at an angle from
weakening the cords and resulting in bruises, broken cords the perpendicular, resulting in side wear.
or ply separation. Underinflation also leads to rim bruises,
as insufficient resistance is provided to prevent the tire
2. Side thrust when rounding turns causes wear on the
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