Will this scrape on steep driveways or inclines?

The LBW design extends the rear profile, so approach angle changes at steep inclines. Measure your current driveway clearance and compare against the OEM bumper's lowest point. If your vehicle already scrapes entering steep driveways, this diffuser will compound that. Otherwise, daily driving clearance remains normal.

Is this functional downforce or cosmetic?

This is functional downforce geometry. The three-piece design creates genuine aerodynamic pressure at sustained highway speeds. You'll notice it most on track or high-speed cornering; street driving benefits are stability-focused rather than dramatic.

What prep work should I do before installation?

Clean the rear bumper mounting surface thoroughly to remove any dirt or old sealant. Inspect your existing hardware for corrosion and replace as needed. Verify all bolt holes align before final tightening. After installation, a UV-protective clear coat layer over the carbon will extend the finish life and protect against oxidation.