Tire Radial Force Variation (Uniformity)
To understand the effects of radial force variation, imagine the tire as a collection of
springs between the rim and the tire tread. If the “springs” are not of uniform stiffness,
a varied force is exerted on the axle as the tire rotates and flexes. This creates a
vibration in the vehicle.
With the increasing need for low tire uniformity values to minimize vibration
complaints, more tire companies are grinding or cutting tires during the
manufacturing process. As a result, free runout measurement is no longer an
accurate indicator of how the tire assembly will perform when rolling under load. Free
run out measurement should not be used as a guide to determine the tires
contribution to the ride disturbance complaint.
The GSP9720JLR takes a measurement of the wheel assembly’s radial force
variation and displays the results. If the GSP9720JLR perceives a problem with the
force variation, it will prompt you to measure rim runout. Refer to “Rim Runout
Measurements,” page 63. When the rim runout data is entered, the GSP9720JLR
extracts and displays the first harmonic force variation contribution of the tire and of
the rim. Refer to “Harmonic Vibrations,” page 133. The GSP9720JLR allows the first
harmonic of the tire to be matched opposite of the first harmonic of the rim to
decrease the first harmonic vibration. The tire and/or rim may need to be replaced or
Forcematched prior to balancing. Refer to “Forcematching,” page 82.
7.3 Radial Force Variation (RFV)
Radial force variation is a term describing the direct measurement of the tire
uniformity forces under load, measuring the variation (up and down) of the load
acting on the vehicle spindle (SAE practice J332).
All tires have some non-uniformity in the sidewall and/or footprint due to variables in
the manufacturing process. Tire uniformity measurement values can be affected by
rim width, rim condition, and/or tire mounting variables. Unlike balancing, there is
often a small amount of RFV remaining in the tire/wheel assembly after
ForceMatching and this is generally acceptable.
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Theory of Operation GSP9720JLR Wheel Balancer Operation Instructions
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