7.2 Road Force® and Runout Measurement
Road Force® Measurement is new to the automotive service industry. It emulates tire
uniformity measurement, which has been measured for years in assembly plants and
manufacturing facilities. Road Force® Measurement can be used to locate and solve
uniformity related tire and wheel vibrations. Tire/wheel assembly uniformity can only
be measured under load.
With recent changes in vehicle sensitivity and increasing ride quality expectations,
wheel balancing alone may not be sufficient to eliminate the tire/wheel assembly as a
vibration source. The GSP9720JLR Road Force Measurement System is a
measuring and diagnostic tool and automatically detects possible vibration sources in
a tire/wheel assembly that cannot be identified by traditional balancing methods. As a
diagnostic tool, the GSP9720JLR reduces the unnecessary replacement of tires and
wheels, significantly reduces troubleshooting time, and offers improved ride quality.
The load roller on the GSP9720JLR performs a computer simulated “road test.” It
measures the tire/wheel assembly to determine how “round” the assembly is when
rolling under a load. If a tire were not exposed to the road surface, then balance
would be more than sufficient. However, not all tires roll round under a load. For
example, an egg-shaped tire/wheel assembly can be balanced about its axis, but an
egg-shaped tire/wheel loaded against a surface would not give a smooth ride.
The GSP9720JLR reduces diagnostic time by identifying vibrations that would not be
detected by the normal balancing procedure. Road Force® Measurement also
detects loaded and free measured runout, force variation of the tire, and balancer
mounting error, allowing superior quality balance of the entire wheel assembly.
Road Force® Measurement is a measurement of the wheel assembly as would be
found from an actual road test of a vehicle. The GSP9720JLR is equipped with a load
roller to take the Road Force® Measurement. The load roller places up to 1400
pounds of force on the spinning tire, and then automatically withdraws from the
wheel.
Road Force® Measurement data may be viewed from the “Show Runout & Force
Variation” popup screen.
Force Variation
Force variation is a correctable symptom of the tire and/or rim being out of round, the
changes in stiffness of the sidewall and footprint of the tire when a load is placed
against it, or a combination of both factors acting on the assembly. Force variation
can cause a vibration, although the unloaded runout of the tire and rim
measure perfectly round and the assembly is balanced.
NOTE: It is important that the air pressure of the tire is set to
specifications prior to the Road Force® Measurement.
Incorrect tire pressure will affect the results.
GSP9720JLR Wheel Balancer Operation Instructions Theory of Operation
135
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