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Old 05-28-2015, 01:39 AM   #1 (permalink)
BabyDiesel
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Thumbs up Coastdown test for an aeromodded 1998 Ford Escort ZX2: Determining Cd & Crr

*Test performed on 05/27/2015*

I was able to get the ZX2 out to do some coastdown testing yesterday morning! This test was to determine the drag coefficient (Cd) and the coefficient of rolling resistance (Crr) of the Ecoscort, a 1998 Ford Escort ZX2. I am using the "measure your drag coefficient" at Instructables.com.

The conditions are as follows: Start/End

Time: 10:44 a.m. - 11:17 a.m.
Temperature: 77*/79*
Dewpoint: 72*
Relative Humidity: 83%/79%
Winds: WSW @ 3/WSW @ 9
Elevation: 197 feet
Air Density (rho): 1.156 kg/m^3
Engine Coolant Temperatures: 205* - 220*
Tire psi: 70 front, 60 rear
Weight: ~2500 pounds

The car has the following aerodynamic modifications:

85% grill block
Covered foglight holes
Windshield wiper cover
front & rear belly pans
Smooth 14x4 space saver wheels
Rear wheel skirts
Driver side and passenger side mirror delete

Stock Cd for an Escort ZX2 is 0.33, stock frontal area is 20.8 square feet, and the stock CdA is 6.9 square feet.

The test was a series of 6 runs in ABABAB fashion. A 7th run was done to test a common effect on aerodynamics(will say more at the end). The road I was testing on was surrounded by trees, thereby negating much of the effects of the light winds. All test were started at 55 m.p.h. and coasted in Neutral for 60 seconds, recording the speed every 10 seconds.

t=0 is when time was started. It is always at 55 m.p.h. t=1 is 10 seconds, t=2 is 20 seconds in, and so forth.

Run #1
t=0 - 55
t=1 - 49
t=2 - 44
t=3 - 40
t=4 - 36
t=5 - 33
t=6 - 28

Run #2
t=0 - 55
t=1 - 50
t=2 - 45
t=3 - 40
t=4 - 36
t=5 - 32
t=6 - 30

Run #3
t=0 - 55
t=1 - 49
t=2 - 44
t=3 - 39
t=4 - 36
t=5 - 33
t=6 - 30

Run #4
t=0 - 55
t=1 - 50
t=2 - 45
t=3 - 41
t=4 - 36
t=5 - 33
t=6 - 29

Run #5
t=0 - 55
t=1 - 49
t=2 - 44
t=3 - 40
t=4 - 36
t=5 - 32
t=6 - 29

Run #6
t=0 - 55
t=1 - 50
t=2 - 45
t=3 - 40
t=4 - 36
t=5 - 33
t=6 - 29

Very consistent!

On the Instructables website, an Excel document is given. The top part is simply plug in your values.



The bottom part is where things get fun! You are in charge of figuring out your Cd and Crr. The objective is to get the line as close to the dots on the graph as possible. The Sum of Error^2 will show how close you are to matching. The lower, the better.



According to my calculations, my new Cd is an amazing 0.269! while my Crr comes in at exactly 0.01. The Crr number is a typical value for a non-LRR car tire's rolling resistance. My coefficient of drag has dropped over six hundredths with only the few mods listed, and I have not yet anything to the rear of the car except for the rear belly pan.

To put it in perspective, a 2nd-gen Toyota Prius has a Cd of 0.26 and the 1st-gen Honda Insight has a Cd of 0.25

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Past threads:
ZX2 modding thread
Ecomodder's Top 10: How they do it!
ZX2 Aerodynamics: Shooting for 0.15 Cd
ZX2 coast-down testing for Cd & Crr

Last edited by BabyDiesel; 05-29-2015 at 05:13 PM..
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