Wheels are made of either stamped or pressed steel discs riveted or welded together.
they are also available in the form of aluminum or magnesium that are die-cast or forged (Figure 42-1).
Magnesium wheels are commonly referred to as mag wheels, although they are usually made of an aluminum alloy. Aluminum wheels are lighter in weight when compared with the stamped steel type.
This weight savings is important because the wheels and tires on a vehicle are unsprung weight.
This means the weight is not supported by the vehicle's springs.