132 8. Theory of Operation GSP9700 Series Road Force Measurement System Operation
During ForceMatching, the first harmonic vibration of the tire is matched opposite of
the first harmonic vibration of the rim to decrease the first harmonic vibration of the
assembly. This reduces the vibration felt inside of the vehicle.
A vibration that occurs twice for every revolution is defined as a second harmonic
vibration. Because there are two vibrations per revolution, the second harmonic
vibration occurs at twice the frequency of a first harmonic vibration:
SECOND HARMONIC VIBRATION
1
2
FORCE VARIATION
12
OVAL-SHAPED
RIM OR TIRE
(R2H)
Multiple harmonic vibrations may also occur. For instance, the third order vibration
causes a three times per revolution vibration:
THIRD HARMONIC VIBRATION
1
2
3
FORCE VARIATION
OUT-OF-ROUND
TIRE
1
2
3
OUT-OF-ROUND
RIM
1
2
3
(R3H)
Multiple harmonic vibrations may occur at any harmonic factor, dependant only upon
the number of vibration components in each revolution.
RADIAL RUNOUT
RADIAL FORCE
VARIATION
RADIAL FORCE
VARIATION
RADIAL RUNOUT
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