A truck frame is the skeletal structure of a truck, and it is typically made out of steel. The steel frame is made up of many different parts, including the side rails, cross members, and suspension mounting points. The frame is what the truck's body is mounted on, and it also houses the truck's engine, drivetrain, and suspension. The frame is a very important part of a truck, and it needs to be strong and durable in order to support the weight of the truck and its contents.