Cadillac XLR validating frontal area calculation

2009 Cadillac XLR

2009 Cadillac XLR

I did a bit more work on frontal area, which appears to support the short-cut we took earlier.

From a thread on Virtual Dyno on HpTuners, The quick way to calculate frontal area is (((w*h)(0.85))/12)/12 = Frontal Area.

For the 2007 base XLR, W=72.3in,  H=50.4in so for a first approximation (((72.3*50.4)*.85)/12/12)= 21.5 ft2.

The question then is the 0.85 factor.  To test that, I downloaded a diagram of the 2007 Cadillac XLR from and pulled just the frontal area into a photo editor.

cadillac-xlr-2007 frontal

Next, I selected the parts of the diagram that were NOT XLR

xlr outline of not xlr

Then I used the photo editor (GIMP) to tell me how many pixels were shaded (20,668) of the total pixels size (149,464) which resolves to 20668/149464 = 13.8%, or 86.2% for the XLR.

That makes the frontal area for the 2007 base XLR, (((72.3*50.4)*.862)/12/12)= 21.8 ft2.  In this case the approximation was good, but I will update my Virtual Dyno XLR profile to 21.8 ft2.

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