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Old 05-26-2014, 10:26 AM   #109 (permalink)
California98Civic
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Join Date: Mar 2011
Location: Coastal Southern California
Posts: 6,299

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 66.42 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
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Quote:
Originally Posted by johnlvs2run View Post
Most of the belly of my car is 8" from the ground, 20% is 7" from the ground, and less than 3% is 6" from the ground. If I'm understanding this correctly, the nose provides drag just like anything under the car, except the belly has more turbulence. Considering the drag would be equal, maybe a nose height of 7 or 7.5 inches would be good, low enough to keep drag away from the bulk of the belly, but not so low to create additional drag. With this in mind, a nose height of 6 inches would be too low is it creates more frontage & drag than is already under the car. Is this right?
I was told to project the airdam only as low as the the lowest protrusions under the car. I did that and it looked more like 4", but I do have my Civic on 13" wheels with 175/70 tires. Cars will seem to vary a little. Not sure why. Probably my measurements!

To my knowledge no one has shown where the balance point if for an airdam--the point at which the aero benefit gets outweighed by the aero penalties. There are informed opinions. And everybody recognizes there is a point at which you begin making more problems for overall drag. But whether 3" or 5" is that pivot point or not... I don't think anyone here has precise enough data. You'll have to judge what seems to be reasonable and workable.
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.



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