[E.Roy]

Cool discussion on this topic. I have a theory that older fullsize vans are likely more susceptible to underbody drag without a deep valence because of their flatter face causing the underbody air path to become a path of less resistance, and thus forcing air underneath and increasing drag. This theory would mean vans might benefit from a deep valence more than other body styles.

Also, I wonder if this played into Ford's Econoline redesign in 2008 where they elongated and stretched the grill 5" forward from the windshield