Body-on-frame is an automobile construction technology. Mounting a separate body to a rigid frame which supports the drivetrain was the original method of building automobiles, and its use continues to this day. The original frames were made of wood (commonly ash), but steel ladder frames became common in the 1930s.
Most small passenger vehicles switched to unibody construction in the 1960s, leaving just trucks and large cars using conventional frames. The switch continued for several decades - even SUVs typically use unibody construction today. Body-on-frame remains the preferred construction method for heavy-duty vehicles, especially those which are intended to carry and pull heavy loads.
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