So, I went and did a bit more coastdown testing this morning. I started with a much higher top speed, 80mph, so that any aerodynamic drag would be much more pronounced. Hopefully the Excel spreadsheet would be able to produce a much more accurate drag coefficient for my car that way.
I tested at a different site today, there was a slight incline, so I made sure that there were equal data points on opposing runs to average each-other out.
So once again, the raw numbers:
Vehicle Weight (with occupant) 2300lbs/1043.26kg
Frontal Area 1.768 m^2
Crr 0.0169
Test run-----V1-----V2----V3----V4-----V5----V6
0 sec---------80-----80----80----80-----80----80 mph
10 sec-------69-----68-----70----68----70----68 mph
20 sec-------61-----59-----62----59----62----58 mph
30 sec-------54-----50-----55----51----55----51 mph
40 sec-------46-----43-----49----42----49----42 mph
50 sec----------------------42----37----43----38 mph
60 sec----------------------34----35----31----36 mph
70 sec----------------------30----31------------- mph
Solve for the Cd and it spits out a very reasonable 0.254
Looks like I've already beat my goal of besting an Insight's 0.26