Radial Force is determined by measuring loaded radial runout and tire stiffness. On
an average passenger car tire/wheel assembly (1000psi spring rate), one thousandth
of an inch (0.001”) of loaded radial runout is equivalent to approximately one pound
of Road Force® Measurement.
Tests on a Chevrolet Lumina were performed using a chassis dynamometer in a
Detroit test lab. The purpose of the test was to determine how much balance weight
would be required to produce the same magnitude of force as a measured amount of
loaded radial runout.
The tests were performed with the vehicle running at different speeds. The first test
was at 50 miles per hour and the second test at 70 miles per hour.
At 50 MPH:
A measured 0.030” (about 30 pounds of road force) of loaded radial runout caused
the same amount of vibration as 1.5 ounces (42 grams) of wheel imbalance at 50
mph. This is 5 times greater than the 0.30 (1/4) ounce imbalance limit.
At 70 MPH:
A measured 0.030” (about 30 pounds of road force) of loaded radial runout caused
the same amount of vibration as 0.75 ounces (21 grams) of wheel imbalance at 70
mph. This is 1 1/2 times greater than the 0.30 (1/4) ounce imbalance limit.
7.6 StraightTrak® Lateral Force Measurement System
StraightTrak® Lateral Force Measurement
Although a vehicle’s suspension checks out to be acceptable, the tire pressure is
correct, the vehicle suspension is properly aligned, and the tire/wheel assembly is
perfectly round when rolling and balanced, the vehicle may still tend to pull or drift
from a straight line. Frequently the cause of this pull is excessive difference in lateral
force between the tires on the steer axle.
This optional feature measures the lateral forces of the tire/wheel assembly and
suggests placement of each tire/wheel assembly (relative to the other tire/wheel
assemblies) on the vehicle so that vehicle pull due to tire lateral forces may be
minimized or eliminated.
NOTE: StraightTrak® requires Lateral Force Measurement
hardware and Version 3.0 software or newer.
Tire Pull Measurement and Correction
Even after tire/wheel assemblies have been balanced, correct inflation has been set,
and suspension has been properly aligned, a vehicle may still pull from a straight line.
The cause of this pull can be due to excessive difference in lateral tire force between
the two tires on the steer axle.
The optional StraightTrak® Lateral Force Measurement (LFM) feature of the
GSP9720JLR is configured to utilize lateral force measurement information taken
from a set of vehicle tires. It provides suggested placements for the individual tires
about the vehicle, such that the net tire pull between the two tires on the steer axle
are minimized to improve or optimize the effects on vehicle handling.
When using StraightTrak® LFM, the basic machine cycle is the same as it has been
for the standard GSP9720JLR, except that several additional tire revolutions have
been added to the end of the cycle so that lateral force measurements can be taken.
The only additional procedure necessary by the operator is to number, or “tag,” the
tire assembly for identification and placement when balancing is completed.
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Theory of Operation GSP9720JLR Wheel Balancer Operation Instructions
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