During tire and wheel diagnosis for a vibration condition, it’s necessary for dealerships to have GM-approved tire force variation measurement equipment that can address imbalance, out of round and tire force variation conditions.
The right equipment is a valuable tool in diagnosing vehicle ride concerns. Some older equipment may not be capable of meeting today’s requirements for road force balancing.

Proper tire and wheel diagnosis includes inspecting the tires and wheels as well as road testing the vehicle.
If the road test indicates a shake/vibration condition exists, use a calibrated off-car dynamic balancing machine to check the imbalance of each tire/wheel assembly.

TIP:
Tire and wheel assembly balancer machine calibration should be checked regularly.
If it’s is used frequently, the machine should be calibrated at the start of every day.
Refer to the Tire and Wheel Balancing procedures in the appropriate Service Information. Some newer machines are self-calibrating.

If a vibration or shake still exists after balancing, any out of round conditions of the wheel and force variation conditions of the tire must be addressed. GM-approved tire force variation measurement equipment can address both.

RFV Measurement

Tire radial force variation (RFV) measurement equipment loads the tire, similar to on the vehicle, and measures radial force variation of the tire/wheel assembly.
To isolate the wheel, its runout must be measured.
If the wheel meets the runout specification, the tire’s RFV can then be addressed. After measuring the tire/wheel assembly under load, and the wheel alone, the balancing machine then calculates the radial force variation of the tire.

The tire force variation measurement equipment can find the low point of the wheel (for runout) and the high point of the tire (for radial force variation).
This allows the tire to be matched mounted to the wheel for lowest tire/wheel assembly force variation.

TIP:
When mounting a wheel to a wheel balancer/force variation machine, always use the wheel’s center pilot hole.
This is the primary centering mechanism on all GM wheels; the bolt holes are secondary. Usually a back cone method to the machine should be used.

Cone Dimensions

Cones and collets are sized slightly larger to allow easy placement onto, and removal from, the shaft.

If the cone/collet ID is 1.578-inches or greater, it is out of specification and should be discarded. Cones/collets that have wear and scars on the OD should also be discarded and replaced.
Do not drop or pile up cones and collets.
They should be placed in their respective locations on a rack or shelf to protect them from damage. On many balancers, there is an integrated shelf available for the collets.
Wipe down the spindle and collets periodically to keep them clean. Do not use harsh cleaners like brake parts cleaner.

Identifying Balancing Machines

There are several GM-approved wheel balancers available through GM Dealer Equipment. Go to www.gmdesolutions.com for more information (U.S.). In Canada, go to www.des-canada.ca.

The Hunter Road Force Wheel Balancer is commonly used for tire force variation measurement in GM dealerships.
There are several generations of the wheel balancer in use, each with different capabilities. Generations 3 and 4 are recommended to ensure consistent, accurate results with difficult vibration conditions.

Some early generations may require several inspections to determine if any major components are worn.

For example, measure around the shaft at several points with a caliper or micrometer. Since the shaft is tapered, measure it at the spring plate, not at the end of the shaft.
If the shaft has more than 0.002-inches of wear (the shaft is 1.572 inches or less), it is out of specification.