Cast Aluminum
Stock wheels are typically made of cast aluminum, which is easy to manufacture and very strong, but weigh in for duty in the heavyweight class. Technological advances in casting techniques have brought the weight of stock wheels down drastically, but they're still much heavier than most aftermarket wheels (of the same size). The price is right for custom aluminum, which motivates the O.E.M.'s to use it.
 The price is right for custom...  The price is right for custom aluminum, which motivates the O.E.M.'s to use it. |  | |
Forged Magnesium
Forged magnesium wheels can cost you as much as $3500 a set. Forged magnesium wheels have the same manufacturing techniques as forged aluminum, except there is up to a 35 percent weight savings while still being competitive in strength to aluminum.