[aerohead]

I won't even try 'em anymore.The wind hasn't stopped blowing in Texas since Hurricane Katrina.I think some of the members have access to a software program to reduce the data.You need a very flat stretch of road,with no traffic,fully-warmed-up-car,and do a minimum of twenty runs,ten in each direction,to cancel out any effects grades might present.There cannot be any wind.NONE!!!!!!!! The gas tank ( diesel ) has to be topped-off before every run,as mass and inertia have tremendous impacts on the coast-downs.You must have complete weather data for the entire test period,as air density and its effect on air drag can vary during the test.Dry-bulb temp,wet-bulb temp,and barometric pressure must be in the bag.You can use a psychrometric chart from an air conditioning company to determine your local air density ( in slugs for US units) by dividing your air's specific weight by the gravitational constant ( 32.2 Ft per second per second ).Test speeds are typically run,coasting down from 70-mph,to 20-mph.You can use a cassette-recorder,calibrated to a stop-watch to record velocities,at one-mph-intervals.Later,you can replay the tape,listen to yourself yelling speeds at the recorder and construct your velocity/time curves on graph-paper.How the vehicle coasts at the lower velocities, establishes your rolling resistance force coefficient,which is fairly constant from 20-to-70,necessary to deduct from your power-curve,to reveal your aero drag component.Newton's F=MA is basically at work here,as it requires so much power( force per unit time ) to alter the momentum of the vehicle from any point to another point.By knowing the mass of the vehicle,air density ,and frontal area ( can be estimated ) ,your drag coefficient will fall out of the equations after the rolling resistance is factored out.I never did it with software,as P.C.s were pretty rare back then.I paid CAR and DRIVER Magazine engineers to test my CRX at the Chrysler Proving Grounds and they kept track of all the worms.It was a bargain! Good luck on that one!