Quote:
Originally Posted by 3-Wheeler
Regarding the Cd, I tried for quite some time to collect data from coast down testing, and ultimately came up empty handed.
It turns out the method used to collect data, like speedometer with a camera, or hand held GPS is not accurate enough to get good coast down readings. My coast down numbers were all over the place after two years of trying.
Oh well, we gave it good shot and now know how NOT to do it.
I would think that a sample rate of let's say 10 Hz or something similar would be needed to get good coast down data, and ultimately a good Cd of the car.
Jim.
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I printed off an enlargement of one of your photos (fabulous!) and compared to the Template and some values I assigned to the Template.
The original car has about 32.3% of Template aft-body.The Template would predict Cd 0.242 at this length and HONDA published 0.25.This is a 3.3% deviation.
From your photo it looks like the new tail brings the car out to 56% of Template aft-body.
At this length the data curve predicts Cd 0.1625.If we throw back in a 3.3% deviation it gives a drag coefficient for your car on the order of Cd 0.167.
This is just an estimate of course.
With a steady speed mpg baseline we could compare 'before' and 'after' mileage and use GM's Cd/mpg relationship to reverse-engineeer the new Cd.
0.167 doesn't seem unreasonable.This would have you in Daihatsu UFE III and GM Precept PNGV territory,a smidgeon below AeroCivic.Fun!
