Car design question

Just thunkin' here.....
Car manufacturers are trying to eek every 10th of a MPG out of cars today. Good for us.
When I sit in a car, any car, I have head room, lots of head room. I'm pretty average in every way (well, my wife would say I'm much better than average in some ways, but we're not talking about flatulence here) and in my 300D I have about 5" with the factory sunroof. Our minivan gives about 7". I've been in SUV's where there's got to be 10" between my scalp and the headliner. I know we have to make allowances for all the not-as-hairy sasquatch among us (Joey48442, I'm looking at you buddy) that tower over everyone else but hmmmm....
How much fuel economy can be gained by making every roofline, say 3" lower? Would they have to make the doors extend into the roof, a-la Ford GT40? Is that soo bad? Not only would the roof line be lower, the the windshield would be raked back a bit more. How much would roll-over protection suffer?
I know the fuel economy savings wouldn't impact you and I that much, but if that's 1% savings multiplied by each vehicle sold it becomes a big CAFE number.

they been doin' that for a while

DrBoost wrote: in my 300D I have about 5" with the factory sunroof

Really? My head brushes the headliner in my 300E.

A lot is done via airflow management. While frontal area is still important, if you can use surfaces to control the air as it flows past the frontal exposure it goes a long way in reducing the force needed to push a car along the road.

Don't forget that the buying populace are stupid and lazy. If the car is difficult to get in and out (because you have to wear it like a GT40 or an Exige) it won't sell.

DrBoost wrote: I'm pretty average in every way ( and in my 300D I have about 5" with the factory sunroof. Our minivan gives about 7".

You may think you are average, but you are not, sir. You either recline like a gang banger, or have several chunks of your spine missing.

Three years ago my 5'1" mother wanted a replacement for he dog hauling astro van. I suggested she look at a ford escape. She thought it felt too small. So she looked at an explorer. Still felt small. Then she tried an expedition and it felt just right to her.

I have a ton of headroom in my Trooper, which comes in handy. I can put bicycles upright in it all day long. SUVs are for utility, not to carry junior and his friends around. So, they have tall roofs.

Note that what I just said expired in the 1990s. They're just to carry junior and his friends around now. The tall roofs are a remnant from the days before soccermoms started driving SUVs.

Modern SUVs, like the pathfinder, exploder, etc. have finally moved away from tall roofs, frames, and solid axles.

Look to Europe - tall cars have become pretty common there because the packaging works well. You can put people in a smaller package and they'll actually be more comfortable. And that's a much more economy-minded market than the US, so the market isn't going to give up efficiency to make room for cowboy hats. I suspect the increased drag from a potentially larger frontal area is offset by a lighter package, which will give better economy in town.

Stupid and lazy doesn't come into it.

Cars are also getting taller because of pedestrian-impact safety measures that require noses be blunter and higher up. Thus why modern cars all have absurdly high beltlines, as well as the loss of retractable headlights.

I suspect the U.S. will continue to buy large and tall vehicles as long as:

1.) gas doesn't approach the prices seen in other parts of the world (oops, I should say gasoline TAXES don't approach those found in Europe).

2.) as long as there are brain-dead folks who equate bigger with safer.

3.) when American malls suddenly run out of the acres of free parking that shopping centers in Europe don't have.

4.) until the next round of the CAFE numbers start to "kick-in" forcing manufacturers to either build smaller and lighter, or force manufactures to put insanely small engines in large vehicles.

FWIW, have you noticed that Ford's F-150 has LOST it's title of most fuel efficient pickup truck? Ram has managed to leap over Ford...and by quite a bit, with their Pentastar V6 and an 8 speed automatic in the Ram truck. Ford: rated 21 highway, Ram: rated at 25 on the highway.

I suspect the U.S. will continue to buy large and tall vehicles as long as:

5) As long as people keep getting bigger and taller.

i was looking at a Prius that i was next to on the interstate and asking myself why the roof is so damn high on those things... but then i got a good look at the profile as i was going by, and it looks like the air flows over the roof better as it is than it would if it was 6" lower. maybe Toyota decided that adding a few pounds to the car was more than offset by getting smoother airflow over the top of the car.