[Big Dave]

If this spreadsheet is valid, I must be doing a bang-up job of improving my aerodynamics and improving engine efficiency by slowing down engine RPM.

Last summer I went to Nashville, TN and back. Slightly cool weather - roughly 70 degrees F. Out and back to same fuel pump so delta y = 0.

I had the full aero treatment: "fastback" bed fairing, air dam, and side skirts.

The trip was entirely an Interstate run and set the cruise on 1700 RPM (70 MPH).

Thev truck weighs 7000 lb. Figure Crr of 0.011 for worn 235-85x16 E-Rated tires pumped up to 100 psi Estimate frontal area at 41 sq. ft. 95% drivetrain efficiency for an overdrive manual. Summer No. 2 diesel.

I got a documented 28.1 MPG over that trip of 600 miles. Playing the variables to duplicate that performance says my Cd is 0.30 and my engine efficiency is 35%.

Am I that good? I figure a open-bed pickup to have a Cd of 0.45 and a diesel engine to have 33% efficency.