http://en.wikipedia.org/wiki/Body-on-frame
http://en.wikipedia.org/wiki/MonocoqueAdvantages
* Easier to design, build and modify (less of an issue now that CAD is commonplace, but still an advantage for coachbuilt vehicles).
* More suited for heavy duty usage and can be more durable.
* Easier to repair after accidents.
* Overall better ride quality [2] for SUVs.
Disadvantages
* Heavier than unibody - lower performance and/or higher fuel consumption.
* Center of gravity is usually higher - compromising stability and handling.
* Less resistant to torsion (flexing of the whole car in corners) - compromising handling and roadholding.
* No crumple zone - higher rate of death and serious injury.
* Higher production costs.
Discuss.In automobiles, it is now common to see true monocoque frames, where the structural members around the window and door frames are built by folding the skin material several times. In these situations the main concerns are spreading the load evenly, having no holes for corrosion to start, and reducing the overall workload. Compared to older techniques, in which a body is bolted to a frame, monocoque cars are less expensive and stronger.
Monocoque design is so sophisticated that windshield and rear window glass now often make an important contribution to the designed structural strength of automobiles. Unfortunately, when a vehicle with a unibody design is involved in a serious accident, it may be more difficult to repair than a vehicle with a full frame. Rust is also more of a problem, since the structural metal is part of the load bearing structure making it more vulnerable, and must be repaired by cutting-out and welding rather than by simply bolting on new parts (as would be the case for a separate chassis). Older cars with separate chassis can still pass vehicle inspection tests (such as the British MoT) with quite advanced rust in the sills (rocker panels) and pillars, whereas in more modern cars these parts are structural and would lead to a test failure. In the United States, in the majority of the states which require safety inspections, vehicles will not pass inspection if rust has perforated components such as rocker panels, floor pans, or pillars - regardless of the type of body construction.
Monocoque designs are favored amongst high-performance cars and racing cars today for their overall structural integrity and the fact that one can design a monocoque out of lightweight materials such as carbon fiber and expect the resulting vehicle to be light, stiff, and stable at high speeds and in tight corners. These types of particularly advanced monocoques can even be molded to create diffusers and ground effects which generate huge amounts of downforce.
Moar info:
http://www.innerauto.com/Automotive_Sys ... sis_frame/
The frame provides a firm structure for the body, as well a good anchor point for the suspension system. There are two types of frames; integral frames (you've probably heard of them as "unibody") and conventional frames. A conventional frame is basically a "one-piece" frame, or two "one-piece" frames fastened together. The frame is extremely rigid in order to keep all the other parts of the car in perfect alignment. The manufacturer takes this type of frame and attaches all the other parts of the car to it, like the way a sculptor starts with a wire frame to build his sculpture on and give it shape. To keep things smooth, rubber insulator blocks, or "pads" are placed between the frame and the other car parts. Because the conventional frame is so important to the structure of your car, (without it, your car would be a pile of doors, hoses, seats, wires and metal) it is usually constructed of heavy steel and welded or cold riveted together. Cold riveting keeps the rivets from shrinking after they cool off. The integral, or unibody, frame is just the opposite. With this type of frame, the body parts are used to structurally strengthen the entire car, and all of the sections are welded into one piece. Sometimes the parts of the body and the suspension system are attached and reinforced. Also, some unibody frames have partial front and rear frames for attaching the engine and suspension members.