Hunter GSP9700 Series, Operation Instructions Manual

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GSP9720JLR Wheel Balancer Operation Instructions Theory of Operation
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The GSP9720JLR measures loaded runout and tire stiffness simultaneously so you
know the magnitude of the vibration force that occur when the assembly is mounted
on a vehicle.
7.4 Radial Force Variation vs. Unloaded Run Out
In the manufacturing community, tire uniformity is called radial force variation. The
uniformity of most tires manufactured today is measured with a machine in
accordance to SAE practice J332. This practice is widely used in the tire industry and
describes tire testing equipment and procedures used to measure radial force
variation of the tire. This practice stresses the importance of measuring force
variation while the tire is under load and does not acknowledge unloaded runout
measurement, for use in tire vibration testing.
Many tire assembly plants have large production lines to measure loaded tire force
variation. Tires, which do not meet uniformity specifications, may be brought into
specification through additional manufacturer’s procedures called force grinding.
Force grinding is done to improve radial force variation by removing small areas of
rubber from the sides and footprint of the tread. Force grinding may not improve (and
in some cases may increase) the unloaded runout measurement.
A tire with large amounts of unloaded radial runout may be vibration free while a tire
with low unloaded radial runout may cause a ride disturbance. In many cases, tire
companies will forego unloaded runout measurement since this information is not as
valuable as tire force variation when it comes to analyzing the causes of tire ride
disturbances.
In the past, when trying to resolve tire/wheel vibration concerns, service facilities
were unable to measure tire force variation. The size and expense of the factory
machines were cost prohibitive. In order to compensate for this lack of field service
technology, many automotive and tire manufacturers have published service limits for
unloaded runout in the tire/wheel assembly.
A standard industry practice has been to measure unloaded runout in the center of
the tire tread using a relatively inexpensive gauge. However, this measurement has
little relationship to the actual amount of ride disturbance felt in the vehicle. For
example, a set of springs may have an unloaded height measurement of equal
length, yet when compressed may create different forces at the same compressed
height.
7.5 Road Force® Vibration Placed into Perspective
In the past, most tire/wheel assembly vibration was considered balance related.
Because of this, tire service professionals tend to relate tire/wheel vibration in terms
of balance weight. Road Force® Measurement will be best understood when related
to the amount of balance weight required to cause a similar vibration in a wheel that
rolls round under a load. In other words, “How much Road Force Measurement
creates a similar vibration caused by tire imbalance?”
Most tire service professionals and factory service manuals agree that residual static
imbalance should not exceed 0.30 oz. on average size wheels and 0.60 oz. on larger
light duty truck wheels.
Loaded Runout Measurement
consisting of
Geometric (Visual) and Constructional (Hidden)
Eccentricities
Tire Stiffness
Measurement
Road Force
Measurement