I drive a Lumina Van, and it definitely gets it's best fuel mileage at 70 - 72 MPH. It has really clean aerodynamics, about the same as an F15 fighter, and is actually more aerodynamic than a Ferrari.
- At 55 MPH, I get 27 MPG.
- At 65, I get 29 MPG
- At 70, I average 32 MPG and all the aerodynamic factors kick in, it develops it's best partial vacuum underneath, and settles down into the suspension and rides at it's most stable as well.