Wheel and tire assemblies are balanced at the assembly plant, using carefully determined specifications provided by engineering.
To maintain the vehicle's designed-in ride and handling characteristics, it may be necessary to balance a wheel and tire assembly after it has been in service for awhile. For instance, after repairing a flat tire.
An out-of-balance wheel and tire assembly is the cause of vibrations, which usually become more severe as road speed increases. Accurate wheel balancing can eliminate or greatly minimize these vibrations, contributing to an improved, smooth ride.
Wheels and tires are balanced and installed to the vehicle as an assembly, and it is not practical to balance either component separately.
Bulletin 07-03-10-017 was recently issued to address a wheel balance condition when using an off-car tire balancer.
TIP: Although this bulletin is specific to the 2008 Malibu with 18-inch cast aluminum wheels, the principles apply to all passenger car wheels.
In some cases, the wheel/tire exhibits vibration at highway speeds even after being balanced. A possible cause is that some cast aluminum wheels may not "chuck up" properly when installed on some wheel balancers. Here's how to avoid problems.
Wheel dimensions are all taken from the hub bore (center hole) of the wheel, and that's where the balancer cone must contact when installed from the back side of the wheel.
This is true of both hub-centric and lug-centric wheels.
Some standard wheel balancer cones may not fit the hole properly. The cone may bottom out against the smaller hubcap diameter (A) instead of contacting the center hole surface (B). If this occurs, the wheel may not be properly centered on the balancer, and the resulting balance is inaccurate.
A Hubcap diameter
B Hub bore (center hole)
What To Do
Before installing the cone to the wheel balancer shaft, check the cone for proper fit to the center hole of the wheel.
Make sure it does not bottom out. The side of the cone should uniformly contact the center hole. If it bottoms out at the hub cap diameter and is not supported by the hub inside bore, it may rock. Do not use a cone that exhibits these conditions.
TIP: It's easier to trial-fit the cone to the wheel before installation on the balancer.
You can contact Dealer Equipment for proper cone specifications (call 1.800.GMTOOLS).
Mounting the Wheel to the Balancer
As described above, make sure the cone contacts the wheel's center hole without bottoming out. Install the cone to the balancer shaft. Install the wheel to the shaft, install the wing nut and tighten.
TIP: Be sure the wing nut is equipped with a non-marring pressure cup, to avoid cosmetic damage to the wheel face.
Care of Balancer Cones
Balancer cones as well as backing/clamping plates and the screw and arbor on the machine need to be kept free of rust, corrosion, grit and dirt. They must not have physical damage from rough handling. Essentially, these parts should be maintained and cared for at the same level as the centering cones and bell clamps of a brake lathe.
The parts can be cleaned of dirt and minor corrosion. Minor dents and damage can be remedied with a small whetstone. Major damage or corrosion requires replacement of the involved component.