Will this diffuser scrape on driveways or steep inclines?

The Aerotune diffuser extends minimally from the bumper line. Test your approach angle before driving steep ramps or highly pitched driveways. If ground clearance is tight on your setup, verify rear overhang on your vehicle before installation.

Does this add functional downforce or is it cosmetic?

This is a styling diffuser designed for visual impact. Real aerodynamic gain requires full-body tuning (splitters, wings, underbody work). The Aerotune profile enhances the rear end's appearance without claiming performance benefits.

What surface prep do I need before painting?

Sand the surface with standard automotive sandpaper and clean thoroughly to remove dust before applying basecoat. Refer to your paint manufacturer's prep guidelines for primer, basecoat, and clear coat application.