Will this diffuser clear speed bumps and driveway inclines?

The diffuser mounts at the OEM rear bumper line, so clearance depends on your vehicle's existing ground clearance and driving style. Approach steep inclines at an angle and avoid abrupt transitions. The three-piece design lets you remove individual sections if you need to assess fitment on your specific driveway or parking area.

Is this functional downforce or cosmetic?

This is a functional diffuser designed to create downforce at speed by managing air flow under the rear of the vehicle. You'll see the aerodynamic benefit during spirited driving or track use. At street speeds, it contributes to the overall look while providing real airflow management.

What prep work is needed before painting?

Sand the surface with fine-grit paper to scuff and clean away any dust or release agent before applying your chosen base coat and clear. The three-piece assembly can be painted as individual panels or fully assembled — both approaches work well depending on your spray setup and masking preference.