How much tire clearance do these add?

The 40mm extension is designed to accommodate wider tires and slightly lowered suspension without rubbing the bodywork. Exact clearance depends on your tire width and ride height, so measure your setup before purchasing if you're running aggressive sizing.

Do I need to drill into my quarter panels?

No drilling required. These mount at factory mounting points using standard bolts, which keeps installation non-invasive and reversible if needed.

Will the edges rust where the flares meet the panels?

FRP won't rust, but the gap between the flare and body will collect dirt and moisture. Seal the edges with flexible trim sealant or weatherstripping during installation to prevent water pooling and corrosion on the underlying metal panels.