[Cd]

I might someday lower my car ( around 2.5" )
I'd like to do an A-B-A coast down test of the results, but it would have to be over a period of several weeks, since I can't do the testing all on one day.

From what I understand, there are a lot of factors that effect a coast down test such as weight, the rolling resistance factor on the tires* , tire pressure as well as tire temperature, the barometric pressure at the time of the test, the exact grade angle of the road, wind velocity and direction, mechanical friction ,....
as well as others that I can't remember.
*( how does a person even find that kind of information ? )

I had read that coast down testing results can fluctuate from run to run even based on the decreased weight of the gas in the tank.

How would you go about doing an accurate test since there are so many factors that change day to day ( or even moment to moment really )

One huge difference that I would have to account for would be the added resistance due to any wheel alignment differences.

A big problem that I have run into in the past, has been the lack of hills where I do my testing.
Can a test be done on a flat surface, or is a hill needed ?