A drum brake uses a drum-shaped (cylindrical) housing, usually made of cast iron, that is attached to the wheel and toataes with it. Inside the drum are curved brake shoes that are forced into contact with the inner drum to provide braking. Drum brakes are simple and generally effective, but less efficient than disc brakes under heavy use or when wet. In modern passenger vehicles, drum brakes are usually used on the rear wheels (in combination with disc brakes on the front wheels).