My 2008 Honda Fit got pushed around by the wakes of semis, strong sidewinds, and the like. Then I put a Beatrush undertray on it and, to my surprise, it all went away. Smoothing out the airflow under the front of the car apparently reduced lift there, and stabilized the vehicle. I give it credit for a 1 or 2 MPG improvement as well. It also hung on like a leech when I hooned the offramps!
