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22 - 4
TIRES AND WHEELS
DIAGNOSIS AND TESTING (Continued)
TIRE NOISE OR VIBRATION
Radial-ply tires are sensitive to force impulses
caused by improper mounting, vibration, wheel
defects, or possibly tire imbalance.
To find out if tires are causing the noise or vibra-
tion, drive the vehicle over a smooth road at varying
speeds. Note the noise level during acceleration and
deceleration. The engine, differential and exhaust
noises will change as speed varies, while the tire
noise will usually remain constant.
SERVICE PROCEDURES
ROTATION
Tires on the front and rear operate at different
loads and perform different steering, driving, and
braking functions. For these reasons they wear at
unequal rates and tend to develop irregular wear
patterns. These effects can be reduced by rotating
the tires at regular intervals. The benefits of tire
rotation are:
• Increase tread life
• Maintain traction levels
• A smooth, quiet ride
The suggested method of tire rotation is (Fig. 6).
Other rotation methods can be used, but they will
not provide all the tire longevity benefits.
MATCH MOUNTING
Tires and wheels are currently match mounted at
the factory. Match mounting is a technique used to
reduce runout in the wheel/tire assembly. This means
that the high spot of the tire is aligned with the low
spot on the wheel rim. The high spot on the tire is
marked with a paint mark or a bright colored adhe-
Fig. 5 Tire Wear Patterns
sive label on the outboard sidewall. The low spot on
the rim is identified with a label on the outside of the
rim and a dot on the inside of the rim. If the outside
label has been removed the tire will have to be
removed to locate the dot on the inside of the rim.
Before dismounting a tire from its wheel, a refer-
ence mark should be placed on the tire at the valve
stem location. This reference will ensure that it is
remounted in the original position on the wheel.
(1) Use a dial indicator to locate the high spot of
the tire on the center tread rib (Fig. 7). Record the
indicator reading and mark the high spot on the tire.
Place a mark on the tire at the valve stem location
(Fig. 8).
(2) Break down the tire and remount it 180
degrees on the rim (Fig. 9).
(3) Measure the total runout again and mark the
tire to indicate the high spot.
(4) If runout is still excessive use the following
procedures.
Fig. 6 Tire Rotation Pattern
TJ
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