Pontiac Fiero 1988 Service Manual page 151

3-10 STEERING, SUSPENSION, TIRES AND WHEELS DIAGNOSIS
• H A R D C O R N E R I N G
« U N D E R I N F L A T I O N
• LACK OF ROTATION
EXCESSIVE T O E ON NON-DRIVE A X L E
L A C K O F R O T A T I O N
H E A V Y A C C E L E R A T I O N
O N D R I V E A X L E
E X C E S S I V E T O E O N
D R I V E A X L E
L A C K O F R O T A T I O N
G 3 3 9 3 Q 3 A N
Fig. 13 Tire W e a r Diagnosis
W e a r Indicators
Fig. 12
The original equipment tires have built-in tread
wear indicators to show when the tires should be
replaced. These indicators will appear as 12.7 mm
(1/2") wide bands when the tire tread depth becomes
1.6 mm (2/32"). When the indicators appear in 2 or
more grooves at 3 locations, replace the tire.
Radial Tire W a d d l e
Fig. 14
Waddle is side-to-side movement at the front
and/or rear of the car. It can be caused by the steel belt
not being straight within the tire, or by excessive lateral
runout of the tire or wheel. It is most noticeable at low
speed, about 8 to 48 km/h (5 to 30 mph). It may also
appear as a ride roughness at 80 to 113 km/h (50 to 70
mph).
The car can be road tested to see which end of the
car has the faulty tire. If the tire causing the waddle is
on the rear, the rear end of the car will "waddle." From
the driver's seat, it feels as if someone is pushing on the
side of the car.
If the faulty tire is on the front, the waddle is
more easily seen. The front sheet metal appears to be
moving back and forth. It feels as if the driver's seat is
the pivot point in the car.
Another more time-consuming method of
determining the faulty tire is substituting tire and
wheel assemblies that are known to be good. Follow
these steps:
1. Drive the car to determine if the waddle is coming
from the front or rear.
2. Install tire and wheel assemblies known to be
good (from a similar car) in place of those on the
end of the car which is waddling. If the waddle
cannot be isolated to front or rear, start with the
rear tires.
3. Road test again. If improvement is noted, install
the original tire and wheel assemblies one at a
time until the faulty tire is found. If no
improvement is noted, install tires known to be
good in place of all four. Then, install the
originals one at a time until the faulty tire is
found.
G33829-3-AN
Fig. 14 Tire Waddle
Radial Tire L e a d / P u l l
Fig.
15
"Lead/Pull" is the deviation of the car from a
straight path, on a level road with no pressure on the
steering wheel.
Lead is usually caused by:
1. Tire construction.
2. Uneven brake adjustment.
3. Wheel alignment.
The way in which a tire is built can produce lead
in a car. An example of this is placement of the belt.
Off-center belts on radial tires can cause the tire to
develop a side force while rolling straight down the
road. The tire will tend to roll like a cone.
The Radial Tire Lead/Pull Correction Chart
should be used to make sure that front wheel alignment
is not mistaken for tire lead.
Rear tires will not cause lead.
VIBRATION DIAGNOSIS
See Figs. 16 through 18 for vibration diagnosis.