If you're unsure about what kind of metal your rim is made out of, there are a few ways to tell. Aluminum rims are usually lighter than steel rims, so if you can pick up your wheel and feel that it's on the lighter side, chances are it's aluminum. You can also look at the color of the metal - aluminum has a silver hue to it, while steel is more of a gray color. Finally, if you have access to a magnet, try holding it up to your rim. If the magnet doesn't stick, then you likely have an aluminum wheel!