[AndrewJ]

So, using the bathroom scale trick (zeroed at vertical) I found that my car takes 35lbs of force to keep it moving on a level surface.

*a note to people who try this method*
smoothing out your stride seems to be an important part of getting an accurate measurement. Just pushing normally produces quite an oscillation of force, making the measurement "jump around"
So focus on the dial of the scale and smooth out your power delivery to keep the dial steady.

So, 35lbs = 160.2 newtons, so on an so fourth. Voila! Crr for my car is 0.0169

Plug it in to Excel, set the solver to solve for Cd (cell F41 only) and it spits out a Cd of 0.194

Hmm, still seems low to me. If the "stock" car is 0.33 and I managed to knock that down to less than 0.20 with a mirror delete, airdam/radiator block , and rear skirts? Seems unlikely.

I think I'm gonna take all the aero goodies off the car tomorrow and run another set of coastdown tests in "stock" form. That way I'll have some idea of how accurate the 0.194 actually is.