Body-on-frame. Body-on-frame is a traditional motor vehicle construction method whereby a separate 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 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 trucks, large SUVs, and heavy trucks.

In the late 19th century, the frames, like those of the carriages they replaced, might be made of wood (commonly ash), reinforced by steel flitch plates, but in the early 20th century, steel 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 knowhow. 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.

History 

The Ford Model T carried the tradition of body-on-frame over from horse-drawn buggies, helping to facilitate high volume manufacturing on a moving assembly line. The use of steel ladder and X frame chassis allowed numerous vehicles to share a chassis and drivetrain while making changes to bodywork and interiors relatively easy, thus keeping costs down and minimizing design time. Over time the technology for unibody construction became economically feasible, assisted in recent decades by computer-aided design. in addition, modern creature comforts, luxury and power-assisted features, and extensive safety reinforcement of vehicles have all added substantial weight, the ability to offset this with unibody construction has proven advantageous.

A handful of  small passenger vehicles switched to unibody construction by the end of the 1930s. The trend had started with cars like the Citroën Traction Avant (1934) and Opel Olympia (a General Motors design) introduced in 1935, and the short-lived, aborted Chrysler Airflow. Trucks, bus manufacturers, and large low-volume cars or those made in the United States continued to use separate bodies on "conventional" frames. Body-on-frame remains the preferred construction method for heavy-duty commercial vehicles (especially those intended to carry or pull heavy loads, such as trucks and some sport utility vehicles (SUVs)) but as production volumes rise, increasing numbers of SUVs and crossover SUVs are switching to unibody frames. Mass-market manufacturers Ford, General Motors, and Chrysler are abandoning true body-on-frame SUVs, opting, when sales volume permits, for more efficient unibody construction. Toyota currently manufactures the most body-on-frame SUVs with the 4Runner, Sequoia, Land Cruiser, Lexus GX, and Lexus LX, followed by Nissan with the Patrol, Armada, and Infiniti QX56/80.

Examples

The following is a list of SUVs and light-duty pickup trucks that have a body-on-frame construction. The list is divided by vehicle category.

SUVs/wagons

Mini SUV
Suzuki Jimny

Mid-size SUV
Toyota 4Runner
INEOS Grenadier
Toyota Fortuner
Toyota Land Cruiser Prado
Lexus GX
Mitsubishi Pajero Sport
Nissan Terra
SsangYong Rexton
Isuzu MU-X
Jeep Wrangler
Ford Bronco
Ford Everest
Ford Explorer (until 2010)
Kia Mohave
Mercedes-Benz G-Class
Mercury Mountaineer
Lincoln Aviator (until 2005)
Chevrolet TrailBlazer (until 2009)
LDV D90
TANK 300
TANK 500

Full-size SUV
Toyota Land Cruiser
Toyota Sequoia
Lexus LX
Cadillac Escalade (ESV)
Chevrolet Suburban
Chevrolet Tahoe
Hongqi LS7
Nissan Patrol
Nissan Armada
GMC Hummer EV
GMC Yukon (XL)
Jeep Wagoneer (Grand Wagoneer)
Ford Expedition (EL/Max)
Lincoln Navigator (L)
Yangwang U8
Infiniti QX80

Compact MPV
Mitsubishi Zinger

Mid-size MPV
Toyota Innova (until 2021)
Isuzu Panther

Pickup trucks

Mid-size pickup truck
Holden Colorado
Ford Ranger
GMC Canyon
Isuzu D-Max
Renault Alaskan
SsangYong Musso
Toyota Hilux
Toyota Kijang
Toyota Tacoma
Mazda BT-50
Mitsubishi Triton
Nissan Frontier
Nissan Navara
Jeep Gladiator
Volkswagen Amarok
LDV T60
GWM Ute Cannon

Full-size pickup truck
Chevrolet Silverado
Ford F-Series
GMC Hummer EV
GMC Sierra
Nissan Titan
Ram pickup
Toyota Tundra

See also
 Backbone chassis
 C-channel
 Coachwork
 Exoskeleton car
 Monocoque
 Skateboard (automotive platform)
 Semi-monocoque
 Space frame
 Subframe
 Superleggera

References

External links
 Ford assembly line featuring body-on-frame car (historic)

Automotive chassis types
Structural system
Structural engineering