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Old 09-04-2007, 08:37 AM   #1
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Calculate the Cd of your car - Instructable

via http://www.makezine.com/blog/ ...

Instructable: Measure the drag coefficient of your car
http://www.instructables.com/id/ELEE7STF5Y3TMFK/

Includes nifty MS Excel spreadsheet you can download and use to enter your own coastdown data.

The writer determined that for his 1992 Geo Metro ...

Cd = 0.370
Crr = 0.0106

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Old 09-04-2007, 08:43 AM   #2
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He's also a member on here too -- I thought he cross linked already
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Old 09-04-2007, 08:50 AM   #3
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Whoops. I must have missed that.

Who's the member? Must be using another name on GS vs Instructables.
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Old 09-04-2007, 09:18 AM   #4
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http://www.gassavers.org/member.php?u=1870


Looks like he didn't post it
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Bike Miles (Begin Aug. 20 - '07): ~433.2 miles

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Old 09-04-2007, 09:41 AM   #5
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That's just weird. I actually used the Garage search tool to look for a 92 Metro (trying to see if the writer had registered his car here) before posting the link. None came up - yet there it is in iwilltry's garage sig/link.

Ah well.

A belated "hello", iwilltry! You know you've got one of the rare combos in a mk3 suzukiclone: 4 doors, 5 gears. The majority of 4-doors were sold as automatics.
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Old 09-04-2007, 11:27 AM   #6
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Quote:
Originally Posted by MetroMPG View Post
The writer determined that for his 1992 Geo Metro ...

Cd = 0.370
FYI, pretty close to Cd = 0.360 for a '92 Metro given here:
http://web.archive.org/web/200410240...drmayf/geo.htm
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Old 09-04-2007, 02:27 PM   #7
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I plugged the results of the coastdown test I did this spring on I-26 in the SC coastal plains into the formula (had to convert from my sec per 10mph drop to the spreadsheet's mph drop per 10 secs) and got a Cd of 0.18. I used the air density and Crr values given in the spreadsheet. To fine tune it better, I'll need to calculate my density altitude for 100 ft elevation, 78F, and 75% RH.
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Old 09-04-2007, 05:34 PM   #8
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Nice. Did you also use the spreadsheet's frontal (A)rea value?
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Old 09-04-2007, 05:58 PM   #9
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No, I couldn't find my car's frontal area listed anywhere on the web, so I measured my car's height (minus ground clearance) and average width and calculated its frontal area.
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Old 09-04-2007, 06:08 PM   #10
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http://web.archive.org/web/200412101...mayf/honda.htm

Note, he was guessing on the area , he guessed 20.56 feet sq. at a cd of 0.360

(and a cd of .18 is AWESOME!!!)
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