How much total drag does my truck create while moving down the highway?
Measure it indirectly!
Run cellphone GPS logger at 1-second interval. Get truck up to speed on flat section of highway, put transmission in neutral, foot off the gas. Let the truck slow down 30 - 45 seconds to get a decent number of data points. Make another data run on same section, but opposite direction to average out effects of wind and any slope.
Import GPS log into spreadsheet.
A linear fit gives you a straight line slope...good enough to determine deceleration...then apply that to F = m * a (you need to know truck's weight) Now you know total drag force at one speed.
Total drag is air resistance (varies with square of speed) plus rolling friction (assume it's constant). OK, do a quadratic/polynomial fit. Now you know rolling friction. Subtract from total drag, and you can determine area-drag (Cd * frontal area) of your truck.
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