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Old 06-20-2009, 04:57 PM   #1 (permalink)
MetroMPG
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Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,316

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)
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Tested: what's the resolution of coastdown testing? Can it register an open window?

I was curious to know what kind of "resolution" coastdown testing has: in other words, what magnitude of aerodynamic change can be revealed by repeated, timed coasting between two speeds.

We know that large changes will show up, eg, here's Skylark's coastdown results of his Versa's Coroplast boat tail:





But what about the smaller things people are doing? Would they show up in coastdowns?

To try to answer the question, I chose one open window as the aero modification I would try to detect.

The speeds tested were 100 km/h (~60 mph) to 50 km/h (~30 mph)

Test was AA-BBB-AA-B

The results seem to indicate that, for my vehicle, at those speeds, a single open window is just at the edge of detectability - the average difference between the A & B results is just above the standard deviation in the control (A) set.

Any smaller aero "mod" would certainly disappear into the statistical noise / variation of the control runs.

Higher test speeds would presumably result in greater resolution.


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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
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