Spaceframe vs. Monocoque
 

What is spaceframe, and what is a monocoque? What are the advantages/disadvantages to each? Are any other Audis other than the A8 built using a spaceframe or monocoque? Thanks.

Space frames were made from many small tubes...
 

creating a three dimensional structure. They used to have large volumes or "space" framed with these tubes. The 300sl was one of the first to use this technique. Lotus, Maserati, Ferrari all used space frames. Monocoques use sheet metal with some boxed elements to spread the loads this technique is just about universal in modern cars. Audi's use of the term in relations to the A8 I believe is a bit of a stretch. The A8 has many boxed elements which Audi is referring to as their space frame but it also has the sheet metal of the traditional Monocoque. It's marketing hoopla.

Space frame vs. Monocoque and others
 

<center><img src="http://www.users.waitrose.com/~enrico/bonfanti-birdcage-chassisr.jpg"></center><p>
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This is the classic space frame, the 1961 Maserati birdcage. The link discusses other chassis types, and the "Audi Space Frame" is shown on the 2nd page.<ul><li><a href="http://www.geocities.com/gkurka2001/CarTech/tech_chassis.htm">Chassis types</a></li></ul>

monocoque == unibody
 

In the US, monocoque is usually referred to as unibody. It simply means that the elements of the car that make up the shape also are the structural portion. This is different from a traditional framed car.

You can think of it this way, look at a pickup truck (the last remaining framed vehicles). The chassis of the vehicle is built up first and the engine and running gear are mounted to it. At this point, the vehicle is completely runnable, despite having no body on it. This is "body-on-frame" construction. When you are done, you could cut the roof off the cab or remove the box from the back with no problem. The frame provides the stiffness.

Now, a unibody car, the box shape of the car is the beginning part, and the engine and wheels and such are connected directly to it. If you cut the roof of of this vehicle you will significantly reduce the stiffness of the whole car.