unibody cars

[e34john]

can someone explain this to me. sorry for being a newb, maybe links can help but i read up on wikipedia and its still little confusing to me. so if my e30 needs its body panels for support, accidents will really ruin the car right? how are the frames on these cars different from something that is built with a real cage. also which bmw models were built like this and which ones arent?

[e34john]

ment to have this in the car section instead of off topic.

[AndrewBird]

Unibody cars are made where the body of the car is part of the structure of the car (where the suspension bolts to, where the engine/drivetrain bolts to etc.). The frame that supports everything is built into the body. With non-unibody cars, there is a chassis that the body mounts to. Here are a few pics showing a non-unibody car:

http://www.eclecticmotorworks.com/pstr617.html

See how the body is separate from the supportive chassis? In a unibody car, all that is one.

Unibody cars can be expensive in crashes due to the fact that the body panels aren't just bolted on into place like a non-unibody car. They are part of the structure of the car. Instead of just unbolting the damaged panel and replacing it with a new one, you must brace the car properly, cut the bad panel out and weld a new one in. This can be expensive and in an e30, due to it's age, will generally cost more then the car is worth.

[e34john]

so unibodies have the panels welded in, but dont e30s have the fenders bolted on?

most trucks are non unibody right because i see how people can just unbolt the bed or i see them lift the entire cab off that ladderbox frame.

[Ferret]

Not all the panels in all unibody cars are part of the struclure. In the E30 for instance the front fenders and and the part below the front bumper are bolted on.
Avner.

[Tangent]

Here's a drawing of a unibody:



The floorpan, sides, and roof are all structular elements. This is why convertibles tend to shake more, a pretty big piece of the body has been removed. This also is why they weigh more. To compensate for the loss they install extra bracing in the remaining parts of the unibody.

how are the frames on these cars different from something that is built with a real cage. also which bmw models were built like this and which ones arent?

A unibody essentially is a cage. The other common car construction type is body-on-frame, which now is only used on trucks and a decreasing number of the largest SUVs. They have a pair of large frame rails that go front to rear that the body is just set on top of and bolted to. Here's a link to a picture of a Ford F150's frame: http://www.dana.com/news/image_libra...f150_frame.jpg The rubber mounts you see going down the side are where the body/bed is bolted on.

Virtually all cars since even before the 70s are built using subframes. It's much lighter and cheaper with the only downside being that they're a bit harder to repair after accidents...

Here's a great site that might help explain the differences: http://www.carbodydesign.com/article...story-1.html#1