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Old 02-09-2016, 11:57 PM   #1 (permalink)
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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)

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Old 02-10-2016, 01:55 AM   #2 (permalink)
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Quote:
Originally Posted by arklan View Post
is it better to have a car with low cd or low frontal area?
Yes.

All kidding aside, it's much easier to lower the Cd of an existing vehicle than to change the frontal area.
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Old 02-10-2016, 02:09 AM   #3 (permalink)
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How fast do you drive in your electric car? I would think that cd would be more important the faster one went.
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Old 02-10-2016, 07:02 AM   #4 (permalink)
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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..
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Old 02-10-2016, 07:08 AM   #5 (permalink)
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Quote:
Originally Posted by arklan View Post
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)
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.
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Old 02-10-2016, 01:02 PM   #6 (permalink)
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How are you getting the 1.5 square meters? That is pretty tiny - on par with the VW XL1.
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Old 02-10-2016, 01:18 PM   #7 (permalink)
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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.
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Old 02-10-2016, 01:29 PM   #8 (permalink)
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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.
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Old 02-10-2016, 05:39 PM   #9 (permalink)
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upgrade

Quote:
Originally Posted by arklan View Post
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)
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%.
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Old 02-10-2016, 06:02 PM   #10 (permalink)
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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.


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