Mike said: ----- Aerodynamic drag is calculated as follows:(courtesy of SAE papers) Aerodynamic drag = 0.5 x (air mass)x(drag coefficient)x(max vehicle cross section)x(road speed+head wind velocity)2 ----- Well, close, but not quite. Change "air mass" to "air density" and you've got it. Eric T. '86 5kS erict@ra.cta.com