What does a body do?

[permanentjaun]

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 come 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?

Matt

[lakota]

"The reasons I come up with are cosmetic purposes, protect passengers and the mechanics of a car from the environment, and for aerodynamics at high speeds."

You've answered your own question...

[permanentjaun]

So then why do we need these heavy bodies?

Car bodies are not meant to be sat on, hit, scratched, etc.

Couldn't a plastic as thin as paper, yet resistant to tearing, be used to significantly reduce weight? I don't understand why more DIY car builders don't weld a space frame chassis and then have plastic bodies that they connect to the chassis to give it the body shape.

Essentially taking a flat piece and mounting it to give it a curve. It shouldn't be that difficult, expensive, and could compare in weight to carbon fiber I bet.

If the piece gets bent or crushed in, simple remove it to return it to a flat piece, then remount it.

Anyone else think this is a good/feasible idea?

[HOTRODPAINT]

There are other concerns that need to be considered.

Attractive styling.
Manufacturing cost, and the startup cost of new technology.
Available in different colors, including metallics and candies.
Being damage resistant. Not many buyers want to fix anything, even once!
The fact that the public is resistant to buying anything too different.

[permanentjaun]

This would only be plausible for either specialized cars or custom cars. Cars built with space frames would be candidates. Very few production cars are built with space frames. Their design requires almost over engineering and the chassis would not be transferable to other designs. An example would be the Ford GT.

Besides that, I don't think using plastics is really a new technology. The idea is like using a piece of paper. It's flat in shape. Make your hand into an L shape, then fold the piece of paper so that it would touch on your index finger and thumb. It forms an arc. Remove the paper from your hand and it returns to the flat shape. That is the idea with the plastics. Depending on where and how it is mounted on the space frame gives it the shape.

I can't imagine that plastics wouldn't be able to be painted in certain styles so long as primers are used.

As far as damage, traditional materials still get damaged from scratching or being impacted.

My idea is similar to Saturns use of plastics so that their panels are dent resistant. The difference is that their plastics are molded and still require specialized tooling to make. With my idea, all you need is to design and engineer it, then hand build that car by mounting the flat panels in certain manners. Saturns plastics also carry a lot of weight with them. I'm looking to use thinner and lighter plastics that don't necessarily have much structure to them.

I would be using the concepts of how a space frame is designed. As single pieces of pipe their structure is weak. Connect them with certain shapes and all of a sudden you have a very strong structure. When the plastic panels are mounted and arc'd into certain positions they will hold their shape at high speeds and be resistant to dents.

Also, consider if a panel is struck and goes from concave to convex, or vice versa, I imagine it would be easier to simply push/pull the panel back into shape. The plastic would be more elastic than metal, and easier to return to the original shape.

What do you all think?

[Matt167]

They started to figure out this kind of stuff in the late '50's early 60's when the unibody came out ( actully the earliest unibody I can think of is a '60 Ford Falcon ), Saturn took this idea and applied it to weight saving plastics in the early 90's

[permanentjaun]

I don't see Saturn as using plastic that is very weight saving. Their two seater convertible roadster is only a few pounds shy of 3000 lbs. My concept has nothing to do with structure either since the space frame would provide the chassis. No monocoque involved. Question is, how light and thin could the plastic be?

[Matt167]

saftey concerns, it would be flimsey, lightweight and any lightweight plastic that I know of, is subject to distortion in high heat conditions and with UV light. Carbon fiber is probably best for a lightweight application, because it is strong and light. Why do you want a lightweight?

[permanentjaun]

Is safety really a concern with it when the space frame chassis is what would protect the occupants and mechanics?

I can't imagine there isn't a lightweight plastic out there that isn't subject to distortion under high heat conditions and with UV light. Plastic bodies have been used on car bodies for decades. I'm just looking for a more extreme lightweight.

Why would I not want lightweight? It's not about how much horsepower you have, it is what the power to weight ratio is. The 2005 Lotus Elise only has 189 horsepower yet it accelerates from 0-60 in 4.9 seconds. The 2005 Ford Mustang GT has 300 hp, but it takes 5.5 seconds to accelerate to 60 mph. Weight is a huge factor when it comes to car construction.

I got my information from www.supercars.net so if my numbers are a little off I apologize. The idea still holds though. Matt

[SprayTech]

The thing is , with a tube type chassis that is weight conscious , makes for hard entry and exit , with a thin layer of so-called plastic . Aluminum . carbon fiber . Saftey has alot to do with design . not HP to weight ratio and going fast , people want comfort , ease of driving .....ect
Why do you think SUV's are popular ? They sit higher , take a better hit ,
Bigger , the feeling of being safe is tenfold .
Plus EPA has alot to do with the design too , curb height , impact crumple zones , weight & ect .........
Sprint cars have to one of the safest and strongest cars built , why do you think they are not on the street ? I could just see my wife in a fancy dress and high heels to go out to a fine diner and ask her to crawl into it from the top over the roll bars .......LOL Oh and the 5 point harness would wrinkle the fancy dress

[Matt167]

Safty is an issue even with the space frame chassie, when somthing could break through the plastic, surpass past the tubes into the passanger compartment ( fence post, road sign or anything like that ), not to mention, in a rollover the plastic would break and turn into schards. Comparing apples to oranges is not the way to go ither, a Lotus is compleatly diffrent in relation 2 a Mustang, gearing is diffrent and the powerband is way diffrent between the 2, it's not all about the weight.

[Henry Rifle]

I'll start thinking about this one when I see the flying car that Popular Mechanics promised us many years ago. Shouldn't we be flying them by now?

[Dave Severson]

It would be fun to see what the engineers would design and build if the government would get the heck out of everybody's business.... The majority of people who buy new cars don't care and wouldn't even know what a space frame was. All most of them care about is that drives nice and is quiet down the road so they can hear good when talking on their cell phone while the kids are in the back watching TV with their headphones on..... As far as a space frame with a composite body, people would never pay what it costs to produce it.... Simple economics.