Will this diffuser scrape on steep driveways or inclines?

The three-piece design sits close to the rear bumper line, but clearance depends on your vehicle's suspension geometry and approach angle. Inspect your driveway grade and compare it against your current bumper height before ordering. If you run lowered suspension, test fit before permanent installation.

Does this diffuser add downforce, or is it purely cosmetic?

This is a styling piece designed to match the A Spec aesthetic. It does not generate measurable aerodynamic downforce on its own. For functional aero, you'd need a full rear wing or splitter system paired with front aero elements.

What prep is needed before installing the diffuser?

Sand and clean the mounting surfaces on your rear bumper to ensure a solid bond. Degrease with isopropyl alcohol and let dry completely. Verify all three pieces fit flush before final fastening. Reference your vehicle's service manual for fastener torque values and any additional mounting hardware your bumper may require.