Re: Increase mpg. Undertray?
An underplate definitely improves MPG, but the whole aerodynamics of the vehicle need to be designed in concert with it. I don't think just adding one is going to help you.
2011 Jeep Grand Cherokee Laredo X. Natural Green Pearl w/ Black interior. QT1, moonroof, 430N, trailer tow.
2013 Lexus GS350