An aluminum rim that's oxidized is usually caused from salt getting under the clear coat and pitting the aluminum. Use sandpaper and a clear coat of paint to protect aluminum car rims with help from car restoration specialists in this free video on car maintenance.
In this video, I'm going to show you how to clean an aluminum rim that's oxidized. There's a good chance that if your rim looks like this it's caused from salt getting under the clear coat and pitting the aluminum. The only way to get it off is to sand it down. Once the pitting is in the aluminum it actually eats the aluminum, so you have to take it off with an abrasive. For this I'm using sandpaper, 220 grit. I like 220 grit because it doesn't take off too much surface of the aluminum, and doesn't scar it up so bad, but it still takes off the oxidation and pitting. Once you've cleaned the rim and you have the bare aluminum it's time to protect it. There's two ways you can go about it. One, you could spray a clear coat on just like that roll of RustOleum you see in the picture. It's just a clear coat of paint that will protect the rim. The other way is you could use a paste wax like you would for the paint on the vehicle of your car. Both will work, but you will have to reply reapply the paste wax from time to time.