Originally Posted by David1
That is not what the corrosion is from initially. When tire shops put the wheel on the balancer that uses a cone seat that goes in the center bore, they usually just slam the thing in the whole or crank it down so tight that it cracks the finish around the lip and then with the centercap in place covers the damage, then the environment starts to attack the bare aluminum and creaps under the paint and spreads out as you can see. The really good balance machines have a motorized lift the raise the wheel so the tech does not drag and damage the finish around the whole. Then the really good machines, at my BMW dealer anyways, the balancer has a hubcentric adapter and the wheel is held in place by the lug holes just as it is when on the car so nothing touches and painted surface.
The corrosion on mine was not caused by a balancing machine because it happened before I did anything with my wheels. The corrosion is caused by water being trapped behind the cap. The wheels are anodized which is a hard coat to prevent the wheels from corrosion and finish scraches. When I removed the caps a gooey water came out and the entire cavity was corroded. Its a bad wheel design. Since I ground grooves to let the water drain I have had no wheel corrosion problems. I also coated the cavity and the rotor face with never seize to prevent any surface rust on the rotor.