Editing Body-on-frame (section)

{{short description|Automobile construction method using a separate body on a structural frame}}

[[File:Auromobile bare chassis frame.jpg|thumb|A [[vehicle frame#Ladder frame|ladder frame]]]]
[[File:ToyotaTundraChassis.jpg|thumb|A 2007 [[Toyota Tundra]] chassis holding the vehicle's engine, drivetrain, suspension and wheels.]]
[[File:IAA 2013 BMW i3 (9833675545).jpg|thumb|The [[BMW i3]] electric car is one of the rare modern passenger cars with a separate body and frame design (2013).]]

'''Body-on-frame''' is a traditional [[motor vehicle]] construction method whereby a separate [[coachwork|body]] or coach is mounted on a strong and relatively rigid [[vehicle frame]] or [[chassis]] that carries the [[powertrain]] (the engine and [[drivetrain]]) and to which the wheels and their [[Car suspension|suspension]], brakes, and steering are mounted. Whereas this was the original method of building automobiles, body-on-frame construction is now used mainly for [[Pickup truck|pickup trucks]], large [[SUV]]s, and heavy [[truck]]s.

In the late 19th century, the frames, like those of the carriages they replaced, might be made of wood (commonly [[ash tree|ash]]), reinforced by steel [[flitch beam|flitch plates]], but in the early 20th century, steel [[vehicle frame#Ladder frame|ladder frames]] or chassis rapidly became standard. Mass production of all-metal bodies began with the [[Budd Company]] and the [[Dodge Brothers]]. All-metal bodies became common in the 1920s, except for Europe, which followed almost a decade later. Europe's custom-made or "coachbuilt" cars usually contained some wood framing or used aluminium alloy castings. Towards the beginning of international automobile assembly and construction, most manufacturers created [[rolling chassis]] consisting of a powertrain, suspension, steering column and a fuel tank that was then sent to a [[coachbuilder]] that added the body, interior and upholstery to the customers specific requests.

In contrast, [[unibody]] or [[monocoque]] designs, where panels within the body supported the car on its suspension, were developed by European manufacturers in the late 1920s with Budd USA (which had a number of large factories in Europe) and its technical know-how. Because of the high cost of designing and developing these structures and the high cost of specialised machinery to make the large pressings required by this style of construction it is not used by low-volume manufacturers, who might construct an equivalent by welding steel tube to form a suitable space frame.