posted
The question makes me sound like an idiot, but I ask in more technical terms.
What does a body do, what is it's purpose?
The reasons I came up with are cosmetic purposes, protect passengers and the mechanics of a car from the environment, and for aerodynamics at high speeds.
Some cars do have monocoques which are the actual chassis of the car, but I am asking from the perspective of a tube frame chassis or traditional truck chassis.
So what else does a body do? What is it designed for? What are its uses?
posted
Not sure what to tell you, but here's my background. I grew up restoring cars with my dad and ended up working as an Insurance Adjuster/appraiser after college. Then went to work in management at a few body shops. You mainly have it right. Most passenger cars and some SUV's are unibody meaning they don't have a frame that the body sits on. They have the main structure of the vehicle and unirails that come off of the front and rear which support primarily the engine and suspension. If you want to see a good example of this, open the hood of a car and look where the fender bolts. This is the upper rail. If you look down to where your suspension and motor mounts are you should be looking at the lower rail. In the back if you look under the rear body you'll see the rear unirails. Unibody cars have inner and outer structure to the body itself. IE inner and outer quarter panels. Inner structure in the front. Typically, the front fenders are bolted on and the quarters in the rear are welded. Trucks tend to have body over frame due to the purpose of their existence. You need beefier frames, drivetrains and suspensions for hauling or towing. The only thing a tube frame is used for as far as I know is racing. My buddies' sprint car was a good example as well as a lot of pure off-road vehicles ie dune buggies or rails.
-------------------- If it wasn't for bad luck I'd have no luck at all. Posts: 1529 | From: Tacoma WA | Registered: Apr 2005
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posted
i never understood why they wouldnt build newer cars based on a racecar tubeframe chassis all hidden within the bodypanels including a rollcage but not even noticable to passengers. who needs crumple zones when the whole car is steel cage covered in cosmetic body panels
Posts: 678 | From: currently in hiding due to investigation | Registered: Oct 2004
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posted
Thanks for the input although I wasn't really asking how the bodies are assembled on the car.
I ask because I am questioning body materials.
You are correct in that space frames/tube chassis are used mainly for race cars. They need to be handmade to exact precisions. Thus, they're not suitable for mass production.
When it comes to the sport of cars and enjoying the thrill, building space frames and custom cars isn't that difficult. Many people have built cars in their own garages.
Why I question about the purpose of a car body is because I don't like the heavy materials of today. Carbon fiber is the new standard for light, but I believe carbon fiber is still too difficult and expensive for do it yourself people.
So consider the uses of a body: 1. Protect the occupants and interior from the environment. 2. Increase Aerodynamics at high speeds of the car. 3. Increase the overall cosmetics of the car.
Car bodies are not meant to be sat on, crashed into, scratched, etc.. Some cars do have crumple zones and such but that is more in the design of the chassis. I will be addressing the design of a space frame so the body does not have that responsibility.
So consider then, plastics.
What if one built a small space frame chassis for a sports car and then used flat plastic as the body. To create shape there are no molds or metal presses. Shapes are made by mounting the plastic on the chassis.
For example, make your hand into an L shape. Then take a piece of paper and touch one end of the paper to the end of your thumb and the other end to your index finger. The paper bows out and forms a curve.
I imagine there is a plastic out there that is durable, tear resistant, scratch resistant, yet very pliable. As you forms arcs, the strength of the shape increases as well.
My question is, would it be all that difficult to produce a car on a tube chassis with very thin and light weight plastic that does absolutely nothing for the structure of the car.
Why do we need these heavy metals and expensive carbon fiber materials?
I imagine a sports car tuba chassis would be about 150 lbs, plastic pody of 50-100 lbs on a small car, small turbocharged 4 cylinder with 5 speed of about 500 lbs, glass of about 100 lbs, suspension and other mechanicals of about 200-300.
Even if I am off by several hundred pounds on my estimates, that could be a very light car, and thus very quick if it has 300+ hp. What do you think hilander? Matt
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Turbokid - Space frame chassis are also very labor intensive to build. It'd take a lot of work to produce them on a massive scale.
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What if one built a small space frame chassis for a sports car and then used flat plastic as the body. To create shape there are no molds or metal presses. Shapes are made by mounting the plastic on the chassis.
Saturn already does this. They are space frame with plastic bolt on or glue on body panels. The only car I can think of that is retty much all carbon fiber is the Koenigsegg CCR built in Sweden.
-------------------- If it wasn't for bad luck I'd have no luck at all. Posts: 1529 | From: Tacoma WA | Registered: Apr 2005
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posted
To me it seems like Saturn still stamps or vacuums their plastics into shape. Their cars are also still considerably heavy. The Saturn Sky, their two seater roadster, is only a few pounds shy of 3000 lbs.
Their plastics seem stiffer and thus heavier. Matt
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Yea, pretty ridiculous. My 66' Checker Marathon is just a bit over 4000. I can't imagine any true driving enthusiast is going to buy the Sky. Matt
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Tell me about it. Mine has the original 283 with only about 160 hp and a 3 speed on the tree. I installed cutouts so it sounds cool, but as far as performance, a thoroughbred she is not.
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had a '63 GMC 1/2 ton short-bed, oooh, let's see...back in the 80s... tweaked the 327 just a little bit and installed a truck transmission with a granny... the lil production hot rods would try to take advantage of the ol' farm truck on my commute to Dallas...hellish traffic...one downshift and throttle into the 4bbl and it leaped like a wolf spider. Got lottsa looks from would-be bullies, lol
quote:Originally posted by permanentjaun: Turbokid - Space frame chassis are also very labor intensive to build. It'd take a lot of work to produce them on a massive scale.
wouldn't it be equally as labor intensive to build a CAD unibody or monocoque chassis? i'm not talking hand made cars or anything like that.
i agree that steel body panels are to heavy and if they could make the frame strong enough and use basically cosmetic plastic body panels suv's could have smaller engines and still accelerate at the same rate with a lighter curb weight... what does the excursion weigh... 8000lbs..? thats one step towards our oil/gas price problem. the lotis elise comes to mind when talking on power to weight... faster in every way than most of detroits big dogs ..with a 1.8 liter.. Posts: 678 | From: currently in hiding due to investigation | Registered: Oct 2004
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posted
Labor intensive? I don't think so. The monocoque is still made out of sheets of metal that can be stamped out. A space frame requires precision and exact measurements.
The beauty of a space frame is that it's lightweight and just as strong. The problem with them is they're complex. For a truck company to use space frames they would need to design space frames for each individual truck. Instead it is much easier to design only a few chassis's and put different bodies on top of them.
Not only truck companies but other passenger vehicles. It's hard enough to design a strong space frame in sports cars. Imagine trying to design one that is solid for a sedan where people don't want pipes running through the middle of the car just as you would see in a Nascar racecar.
What I'm wondering right now from my original question though is just how well engineered can something be such that the plastic is so light and strong. For instance could a plastic be used that was only a pound or two per square foot? If so I easily see cars being built that almost give motorcycles a run for their money. Matt
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