frontal area vs cd
 

is it better to have a car with low cd or low frontal area? if u can only have 1
been googling this and reading about cda but havent found a clear cut explanation
my car has a frontal area about 1.5m2 but a cd of 0.4~
im thinking of which direction i should upgrade my car (its electric)

Yes.

All kidding aside, it's much easier to lower the Cd of an existing vehicle than to change the frontal area.

How fast do you drive in your electric car? I would think that cd would be more important the faster one went.

I think u can enjoy both; larger frontal area not letting as much air under car decreasing cD.. does that make sense? If the increase in frontal area is the addition of an airdam or lower bumper?
And would lowering a car count as the same thing as decreasing frontal area..

You need to define your goals, and then design a plan to achieve those goals.

Low speed rock crawling (shorter wheelbase + wider track)?

High speed cruising (longer wheelbase + narrower track)?

City car under 35 mph where aerodynamics are less important?

How much HP are you working with?

Cool Charts:
Aerodynamic Drag - Craig's Website at Backfire.ca

I think once you fit for driver and passenger packaging, and width/track and length of wheelbase for handling, then aerodynamics can be applied.

Or you could come up with the perfect shape and just squeeze people in their any which way.

Your choice, your decision, in the end it will be a compromise of sorts.

How are you getting the 1.5 square meters? That is pretty tiny - on par with the VW XL1.

It's not an either/or question. Kind of like, "What can't I live without- air or water?"

You want low CdA, no matter how you can get it.

It's not frontal area, but cross section, at the point where the area is greatest. Obviously, for anything except maybe a cabover semi, the area is greatest about where the driver sits, and much less at the front.

As for which matters, both are equally important. Drag depends on the product CdA. When designing or choosing a car, it's probably easiest to change A: you just buy e.g. a Miata instead of a Suburban.

upgrade
 

For an 'upgrade', it would not be practical to shrink the car by any means.
At Cd 0.4 and Af 1.5 m-sq you're at CdA 0.60 m-sq ( 6.456 sq-ft ).
If you went completely aerodynamically insane you could have a road-going Cambridge University CUER solar racer body of Cd 0.10. This would be 25% of your current drag coefficient.
Your new CdA would be 0.15 m-sq ( 1.614 sq-ft),25% of your current figure,for a 75% drag reduction.Your 'fuel economy' would increase about 37.5%.
http://i1271.photobucket.com/albums/...itled12_15.jpg

Aerodynamics - the 'art' of parting the air in front of you, slipping smoothly thru the separated air, and then merging the air back together behind you, as if you never were there.

Well, there's the old hotrod "chop & channel" approach: https://en.wikipedia.org/wiki/Chopping_and_channeling

Indeed, I've sometimes wondered how hard it would be to do that to a small 4WD like the (older) Honda CR-V or Toyota Rav4.

Is it the "Blue Turd" we are talking about?

DIY Electric Car Garage - show
http://www.diyelectriccar.com/garage...get_image/3874


DIY Electric Car Garage - index
I wonder if you could cut out some of the rear roof and do a bubble matching the Aero-Template.

Picture this as a starting point: Suzuki Mighty Boy
http://www.icbm.com.au/mightyboy/suzuki_history.htm
http://www.icbm.com.au/mightyboy/his...ages/rotty.jpg

What I just proposed would help eliminate a huge tapering cantilever of a rear end.

I was under the impression that Australia was pretty strict on what modifications they allow to road going vehicles. If this is the case, then unseen modifications such as a belly pan might be your better option.

That is the definition of frontal area: the largest area of the entire vehicle as you see it from the front. It includes the wheels, side mirrors, roof, any protrusions underneath - everything you can see from the front.

chop and channel
 

Man,you'd have to really brave to take on a unibody construction like that.The old body-on-frame construction modification would be a walk in the park in comparison.:p

IDK, it looks like this would really stiffen up a Yaris:

http://ecomodder.com/forum/member-fr...1-470-1108.jpg

There is not much on-line about the Monoposto, in English, at least.

Don't know who uses that definition, but it seems a misuse of language at best, since the area would be identical to everything you can see from the back.

I tell people it's like the hole Wile E. Coyote makes in the fake road painting* before he falls off the five-mile-high cliff.

*Or some such
http://i146.photobucket.com/albums/r...psyhh4qtqz.jpg

I... don't know anyone who would want to hear about it...

Ooooh! You are one of those people who insist on pronouncing those palendromes backwards.....i can't stand that. ;)

What? That's the definition of "frontal area" everyone uses here.

http://ecomodder.com/forum/showthrea...ement-462.html

http://ecomodder.com/forum/showthrea...etro-2439.html

http://ecomodder.com/forum/showthrea...hod-11690.html

"Frontal" because cars normally move forward through the air, so the high pressure is at the front....

Xist -- The picture was from SEMA, probably 2013. Titled 'sema cool 11 470 1108', from some car blog or another.

It was squirreled away in one of my albums. There's other stuff there in case I find some need or use for it.

Lowering frontal area.

1. The Chop
http://ecomodder.com/forum/showthrea...etro-4892.html
http://www.explodingdinosaurs.com/20.../IMAGE_441.jpg

2. The Tandem
Modified Metro XFi: throwing convention to the wind - MetroMPG.com
http://metrompg.com/posts/photos/1989xfiaerocar1-m.jpg


Lower Cd

1. The Rear Boat Tail
Aerodynamic tail makes Geo Metro even cooler | Hackaday
http://i.ytimg.com/vi/1sQFtd-bTfw/hqdefault.jpg

Subcompact Culture - The small car blog: Behold: The Boat tail Metro
http://2.bp.blogspot.com/-escIetFRaB...tail_metro.jpg

so the reason i ask, i was thinking of whether or not i should get a prius roller or maybe a daewoo matiz roller to transfer my electric goodies in to
the blue turds gearbox uses oil like it was petrol and has a few other things that come with a near 40 year old car
modifying cars here in australia is suppper strict, i put a belly pan and a kind of front air dam on it, and i took the passenger mirror off, thats as far as im able to go.
i was also looking in to making a car from scratch that looks like that solar racer but the amount of paperwork and regulations and stuff id have to go through... i dont have the time, the sun is going to turn in to a red giant in another 5bil years

also to add, i drive this car to work 6 days a week which is a 14km round trip, theres not much stop and go but its through the town and its hilly
on sunday i drive on the freeway for a 70km round trip on fairly flat ground,

No, what I understand when I hear "frontal area" is what you'd get if you drove straight into a brick wall - the area of the FRONT of the car.

I like to think of it as it relates to a train. Doesn't matter if it's a streamlined bullet train or an old box car. Doesn't matter if it's one car or 100, the frontal aera is the same...
And that's how big the entrance to the tunnel better be!

Now we have a scenario to respond to.

In the last few years, junkyards have quietly filled up with OEM electrical components that are likely superior to what you used in your conversion. Carefully evaluate what you have—batteries, controller and motor. Transferring the old stuff into a new body may not be the best option (although it may also be).

A stanced Prius would get my vote. but you're up against those fenderwell clearance rules.

Also, the frontal area of a pontoon-fendered car is greater that the cross-section at the B-pillar. It doesn't become important until you get to jet planes with their 'area rule'.

frontal area
 

'Frontal area' is a *******ization of 'projected frontal area'.It is the area of the shadow of the vehicle projected onto a screen,directly behind it,cast by parallel light (sunlight),from directly ahead.You'd get exactly the same shadow if the light source was from directly behind.It's merely a convention used in industry.
The area has nothing to do with the front of the vehicle.

If you backed the vehicle through a brick wall the result would be the same.

It shouldn't even be called frontal area but it is. We can't even call it "maximum cross-sectional area" because that wouldn't necessarily be right either. Ah well. People call engines "motors" all the time but we live with it.

Are we all being punked? How does someone who has been here as long as you not know what the rest of us mean when we talk about "frontal area"? In your definition, where does the "front" of the car end? Your two examples seem to contradict each other re: what constitutes frontal area.

Um...everyone here. The staff at the A2 wind tunnel. Cyclists. NASA. The EPA. Computer geeks. Pretty much anyone who talks about, works on, experiments with, or is interested in aerodynamic drag.

Of course, if you're just looking for a vocabulary crusade, there are more fruitful areas to address--starting with the general use of "aerodynamic" as a qualified property meaning "streamlined."

For that scenario it depends on the velocity and strength of the vehicle (amount of deformation) plus the strength of the wall (amount of penetration).

https://4.bp.blogspot.com/-4uBqJ9emp...18179305_n.jpg
http://justacarguy.blogspot.com/2016/02/even-gt-40-was-crash-tested-at-41-mph.html

Clarification: if "frontal area" is not the same as cross-section (as jamesqf's first post indicates: "It's not frontal area, but cross section"), where does the front end?

clarification
 

With quasi-streamline half-bodies and streamline half-bodies,the maximum area cross-section WOULD occur with the projected frontal area
http://i1271.photobucket.com/albums/...titled7_19.jpg
http://i1271.photobucket.com/albums/...Untitled_2.jpg
With something like the Morelli shape,the maximum cross-section would NOT occur with the projected frontal area.
http://i1271.photobucket.com/albums/...titled8_22.jpg
By establishing Cd based upon projected frontal area,we keep apples apples,and oranges oranges.

Just a small comment

Frontal area x CD gives drag for a non "streamlined" shape,

There are two types of drag - form drag and skin friction

If you can properly streamline a shape such that the air follows the surface, does not detach and rejoins nicely
Which is nearly impossible in a ground vehicle

Then you eliminate "form drag" and you end up with skin friction which is proportional to the "wetted area" and NOT related to the frontal area

Form drag isn't eliminated, it's minimized. So what are the relative proportions of drag/friction?

Attachment 19721
This is a good example the frontal area being at the rear. Frontal area will get smaller each time a stage is released

Frank Lee
Quote:
In your definition, where does the "front" of the car end?
on this 🚀 at the rear including the stabilizing fins just in front of the nosal

For that scenario it depends on the velocity and strength of the vehicle (amount of deformation) plus the strength of the wall (amount of penetration).

The way you described the hole should be 1-4" in Diameter with no penetration misconception

The brick wall ex would have a round hole 33' Diameter plus tailfins fact

Simples just go buy a car that starts with world class CDx, less than 6 SqFt.

from the Wiki

CdA sqft CdA m2 Automobile model
2.04 sq ft 0.190 m2 2011 Aptera 2 Series
2.10 sq ft 0.195 m2 2013 Urbee 2[
2.50 sq ft 0.232 m2 1986 Twike
2.54 sq ft 0.236 m2 2002 Opel Eco-Speedster
2.69 sq ft 0.250 m2 2009 Loremo
2.784 sq ft 0.2586 m2 2010 Edison2 Very Light Car
3.00 sq ft 0.279 m2 2011 Volkswagen XL1
3.95 sq ft 0.367 m2 1996 GM EV1
5.00 sq ft 0.465 m2 2005 Mercedes-Benz Bionic
5.10 sq ft 0.474 m2 1999 Honda Insight
5.40 sq ft 0.502 m2 1989 Opel Calibra (8 valve)
5.58 sq ft 0.518 m2 1993 Mazda RX-7 FD (base model)
5.70 sq ft 0.530 m2 1985 Subaru Alcyone/XT/Vortex
5.71 sq ft 0.530 m2 1990 Honda CR-X Si
5.74 sq ft 0.533 m2 2002 Acura NSX
5.76 sq ft 0.535 m2 1968 Toyota 2000GT
5.80 sq ft 0.539 m2 1986 Toyota MR2
5.81 sq ft 0.540 m2 1989 Mitsubishi Eclipse GSX
5.86 sq ft 0.544 m2 2001 Audi A2 1.2 TDI 3L
5.88 sq ft 0.546 m2 1990 Nissan 240SX / 200SX / 180SX
5.90 sq ft 0.548 m2 2015 BMW i8 [142]
5.92 sq ft 0.550 m2 1994 Porsche 911 Speedster
5.95 sq ft 0.553 m2 1990 Mazda RX7
5.96 sq ft 0.554 m2 1993 Mazda RX-7 FD R1(R2)

The first 9 on the list are rocking horse poo and unicorn horns. Others like the Toyota 2000GT are £1 million and/or very rare, less than 1000 Porsche speedsters. The i8 is a bit expensive to start chopping around.

Then make a choice between 2 seat or 2+2. But beware of the 8 valve Opel Calibra it's only got 1/2 a cooling system so most of it's advantage over the 16V/turbo/V6 models is cooling / engine bay drag. Honda Insight also has small radiator with blanking plate.

Mazda RX7 FD appears 3 times with different "aero" trim. So now you have a choice of about 10 cars.

Lowering a car only reduces the frontal area by the area of the tyre that is hidden. 25mm drop with a 205mm tyre = 4 x 0.205 x 0.025 = 0.02 m².

I'm interested in that question too but more thinking along the lines of :

Would it be plain stupid to add a perfectly shaped roof addition in order to get a better angle at the back ?

Thanks in advance.

Pretty much this. Go buy an Insight with a blown engine/crapped out CVT and a dead hybrid battery. Stick your electric bits in. Go.