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AndrewJ · 01-02-2008, 07:38 PM

So I actually got my lazy butt off of the couch today and went out and did some coastdown testing.
Here be the results.

Methodology:
using Iwilltrys' instructable "Measure the drag coefficient of your car"
I used a camera mounted on a tripod in the backseat to record the data points. I used my remote shutter control to take pictures of the speedometer every 10 seconds as indicated by my stopwatch.

Frontal area was measured using this technique but with photoshop's histogram tool instead of GIMP.

The Raw Data:

Vehicle Weight (with occupant) 2300lbs/1043.26kg

Frontal Area 1.768 m^2

Test run-----V1-----V2----V3----V4-----V5----V6
0 sec---------55-----55----55----55-----55----55 mph
10 sec-------49.5---51-----51----50----49.5--50 mph
20 sec-------44-----45.5---45----44----43----43 mph
30 sec-------38-----40-----40----38----37----38 mph
40 sec-------33-----35-----35----33----32----33 mph
50 sec-------29-----30------------28----27----27 mph
60 sec-------25--------------------23----22----23 mph
70 sec------------------------------------19----19.5 mph

The Results

Well, here's where it gets tricky. I used the solver function in the excel spreadsheet, but it keeps giving me really strange numbers, impossible numbers. So I tried my best to eyeball the numbers to get all of the data points to line up, here's what I got.

--------Solver-------Me eyeballing it
Cd------0.062-----------0.20
Crr-----0.0218----------0.018

Perhaps someone who has done this before can lend a hand?

01-02-2008, 07:38 PM	#22 (permalink)
AndrewJ Awesomeness personified Join Date: Dec 2007 Location: Columbia, MO Posts: 642 Harold - '94 Honda Civic CX 90 day: 54.51 mpg (US) Margot - '08 Surly Big Dummy Thanks: 0 Thanked 28 Times in 18 Posts	The Data is in..... So I actually got my lazy butt off of the couch today and went out and did some coastdown testing. Here be the results. Methodology: using Iwilltrys' instructable "Measure the drag coefficient of your car" I used a camera mounted on a tripod in the backseat to record the data points. I used my remote shutter control to take pictures of the speedometer every 10 seconds as indicated by my stopwatch. Frontal area was measured using this technique but with photoshop's histogram tool instead of GIMP. The Raw Data: Vehicle Weight (with occupant) 2300lbs/1043.26kg Frontal Area 1.768 m^2 Test run-----V1-----V2----V3----V4-----V5----V6 0 sec---------55-----55----55----55-----55----55 mph 10 sec-------49.5---51-----51----50----49.5--50 mph 20 sec-------44-----45.5---45----44----43----43 mph 30 sec-------38-----40-----40----38----37----38 mph 40 sec-------33-----35-----35----33----32----33 mph 50 sec-------29-----30------------28----27----27 mph 60 sec-------25--------------------23----22----23 mph 70 sec------------------------------------19----19.5 mph The Results Well, here's where it gets tricky. I used the solver function in the excel spreadsheet, but it keeps giving me really strange numbers, impossible numbers. So I tried my best to eyeball the numbers to get all of the data points to line up, here's what I got. --------Solver-------Me eyeballing it Cd------0.062-----------0.20 Crr-----0.0218----------0.018 Perhaps someone who has done this before can lend a hand? __________________ "I got 350 heads on a 305 engine. I get 10 miles to the gallon. I ain't got no good intentions." - The Drive By Truckers.