GMC 1986 P-Truck Service Manual page 363

3E-6 WHEELS AND TIRES
2.
3.
Tire
A.
Tire Reference Mark At 12 O'clock
B. First Measurement (High Spot)
C. Valve Stem At 12 O'clock
D. Second Measurement (High Spot)
E. Tire Reference Mark At
Figure 4—Checking Tire To Wheel Vectoring
• Disregard any instantaneous dial jumps due
to welds, paint runs, scratches, etc. on the
wheel.
• Rotate the tire and wheel assembly (or just
the wheel) and note the amount of variance
(runout) from zero. Locate and mark the
high spot.
. If th e re is a la rg e d iffe re n c e in ru n o u t
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measurements from ON vehicle to OFF vehicle,
the runout problem is likely due to excessive
runout of the bolt circle or hub.
7. If measured runouts are not within the guidelines
(located in " Wheel Runout Specifications" at the
end of this section), proceed to " Vectoring" to
correct the problem.
VECTORING
Vectoring is a technique used to reduce radial or
lateral runout—and even dynamic balance on tire and
wheel assemblies. Vectoring can be accomplished by
positioning of the tire on the wheel and positioning of
the tire and wheel assembly on the hub/rotor.
Im portant
Always rebalance the tire and wheel
assembly after vectoring.
Tire To Wheel Vectoring
1. Determine which runout needs to be minimized.
• Determine visually.
2. If ra d ia l ru n o u t is the p ro b le m , take a
measurement on the center tread rib.
• If the trend is uneven, wrap tape tightly
a round the tire ,
magnitude, and mark the high spot location
(figure 4).
B
B-07455
O'clock
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re co rd the ru n o u t
A. Valve Stem And Tire Reference Mark
At 12 O'clock
B. First Measurement (High Spot)
C. Valve Stem At 12 O'clock
D. Second Measurement (High Spot)
E. Tire Reference Mark At
Figure 5—Tire To Wheel V e c to rin g -
Excessive Tire Runout
3. If la te ra l ru n o u t is the p ro b le m , take a
measurement on the sidewall just below the edge
of the tread shoulder.
• Record the runout magnitude, and mark the
high spot location.
4. Mark the tire sidewall at the valve location.
• This is the 12 o'clock position.
• The location of the high spot is always with
respect to the clock location on the wheel.
5. Break the tire and wheel assembly down on a tire
mounting machine and rotate the tire
(180°) on the rim (figure 4).
• Reinflate the tire and measure the runout in
question.
• Record the magnitude and the location of
the high spot. (Valve stem is 12 o'clock.)
. If the clock location of the high spot remained at
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or near the clock location of the original high
spot, the rim is the major contributor to the runout
problem.
• Confirm by removing the tire from the wheel
and check the wheel rim runout.
• If the wheel rim runout exceeds guidelines,
replace the wheel.
7. If the clock position of the high spot is
from the original high spot, the tire is the major
contributor to the runout problem (figure 5).
• Replace the tire.
. After correcting the tire to the wheel vectoring,
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rebalance the wheel and tire assembly.
Tire And Wheel Assembly To Hub/Rotor Vectoring
1. Mark the wheel hub bolt nearest the valve stem
for reference (figure
2. Rotate the assembly two wheel hub bolts and
recheck the runout (figure
• Several positions may have to be tried to
locate the optimum location.
O'clock B-07505
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hours
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hours
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