EcoModder Forum Measure the drag coefficient of your car

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EcoModding Apprentice

Join Date: Feb 2008
Location: Italy, Morbegno (SO)
Posts: 151

tigra AERO - '96 opel tigra
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Measure the drag coefficient of your car

iwilltry has write a tool, for measure the drag coefficient of cars.
available at http://www.instructables.com/id/Meas...t-of-your-car/

After to have watched this one, I have modified it in order to greater precision.
The change, it is in the air density parameter: in origin, this value was fixed to 1.22 Kg/m^3, now, it is calculated in order of air density based on the climatic condition, and isnt' required to adjust it for altitude

for example, now, in Rome, with 15°C temperature, 48% of humidity and 1012mBar pressure, the air density is of 1.1735Kg/m^3.

New version, is avaible :http://forum.ecomodder.com/attachmen...1&d=1206974721

Attached Files
 stima cx fabrio.zip (82.1 KB, 384 views)
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 03-31-2008, 12:33 PM #2 (permalink) EcoModding Apprentice     Join Date: Feb 2008 Location: Italy, Morbegno (SO) Posts: 151 tigra AERO - '96 opel tigra Thanks: 9 Thanked 38 Times in 18 Posts no comment? __________________ .................................................. ................... http://aeroproject-fabrio.blogspot.it/
 04-05-2008, 06:37 PM #3 (permalink) EcoModding Apprentice     Join Date: Feb 2008 Location: Italy, Morbegno (SO) Posts: 151 tigra AERO - '96 opel tigra Thanks: 9 Thanked 38 Times in 18 Posts I am thinking: but the inertia moment of the wheels? and the gearbox (or only the differential) losses? The inertia wheels, isnt' a big problem: it is possible to add an ipotetical additional mass at the car, this system, translate up the total curve of deceleration. But the losses from gearbox? I have serch in the internet for to look the course of curve of loss for to know if it is liear or exponential. ah, after indagation, I discovered that the rolling resistence isnt' constant, but in functio of speed: Rr= F+K*Speed F= Crr*Mass K=??? __________________ .................................................. ................... http://aeroproject-fabrio.blogspot.it/
 04-05-2008, 08:39 PM #4 (permalink) Batman Junior     Join Date: Nov 2007 Location: 1000 Islands, Ontario, Canada Posts: 22,373 Blackfly - '98 Geo Metro Team Metro Last 3: 70.09 mpg (US) MPGiata - '90 Mazda Miata 90 day: 52.07 mpg (US) Winter beater Metro - '00 Chevrolet Metro 90 day: 61.98 mpg (US) Fancy Metro - '14 Mitsubishi Mirage top spec 90 day: 58.72 mpg (US) Even Fancier Metro - '14 Mitsubishi Mirage top spec 90 day: 70.75 mpg (US) Appliance car - '14 Mitsubishi Mirage ES (base) 90 day: 50.04 mpg (US) Thanks: 3,916 Thanked 6,766 Times in 3,509 Posts I've seen this spreadsheet before, but haven't used it. I think AndrewJ used it to estimate the change in Cd of his Civic. __________________ Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata Honda mods: Ecomodding my \$800 Honda Fit 5-speed beater Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage. Ecodriving test: Manual vs. automatic transmission MPG showdown EcoModder has launched a forum for the efficient new Mitsubishi Mirage www.MetroMPG.com - fuel efficiency info for Geo Metro owners www.ForkenSwift.com - electric car conversion on a beer budget
 04-05-2008, 08:45 PM #5 (permalink) Awesomeness personified     Join Date: Dec 2007 Location: Columbia, MO Posts: 642 Harold - '94 Honda Civic CX 90 day: 54.51 mpg (US) Margot - '08 Surly Big Dummy Thanks: 0 Thanked 28 Times in 18 Posts Yep, I used it to calculate my Cd a few times. I thought about changing the air density value, but I looked it up and it's based at sea level, Since I'm right at sea level, I didn't mess with it. __________________ "I got 350 heads on a 305 engine. I get 10 miles to the gallon. I ain't got no good intentions." - The Drive By Truckers.
 04-05-2008, 09:29 PM #6 (permalink) Liberti     Join Date: Feb 2008 Location: California Posts: 504 Thunderbird - '96 Ford Thunderbird 90 day: 27.75 mpg (US) Thanks: 0 Thanked 7 Times in 7 Posts Not 100% sure, but air density values pulled out of books tend to be at STP. Standard temperature and pressure are not common values one would see at sea level. For example, I believe standard temperature is 0C... I don't know how big a difference the true air density would make on Cd accuracy, but if the value was pulled out of a book it is probably off. - LostCause
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Quote:
 Originally Posted by LostCause Not 100% sure, but air density values pulled out of books tend to be at STP. Standard temperature and pressure are not common values one would see at sea level. For example, I believe standard temperature is 0C... I don't know how big a difference the true air density would make on Cd accuracy, but if the value was pulled out of a book it is probably off. - LostCause
In the aviation world standard temperature and pressure is 29.92 @15 C at seal level.
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Liberti

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Quote:
 Originally Posted by Lazarus In the aviation world standard temperature and pressure is 29.92 @15 C at seal level.
Well, in my world...

You are right, but the idea of inaccuracy is still there (albeit, lessened...).

- LostCause

Batman Junior

Join Date: Nov 2007
Posts: 22,373

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.07 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 50.04 mpg (US)
Thanks: 3,916
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Quote:
 Originally Posted by Lazarus ....at seal level.
I imagine that's usually pretty close to sea level?
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Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my \$800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown

EcoModder
has launched a forum for the efficient new Mitsubishi Mirage
www.MetroMPG.com - fuel efficiency info for Geo Metro owners
www.ForkenSwift.com - electric car conversion on a beer budget

 04-06-2008, 04:02 PM #10 (permalink) EcoModding Apprentice     Join Date: Feb 2008 Location: Italy, Morbegno (SO) Posts: 151 tigra AERO - '96 opel tigra Thanks: 9 Thanked 38 Times in 18 Posts boys, I have big esteem for you, but if you answer therefore, I take care myself ! the file "stima Cx fabrio.zip" is a my modified version from original by Iwilltry. Added new function for evaluating correct air density it is an improvement. You could try sone variation in climatic condition for know itse impact. This is, argument of my first post and you answers only after my second post when, I have exposed a new problem. I must cry or laugh? ah, Basjous has extimated drag coefficient of aerocivic using the original spreadsheet __________________ .................................................. ................... http://aeroproject-fabrio.blogspot.it/