Are MagSafe car mounts strong enough to hold an iPhone Pro Max over bumps?

Mostly yes, but with caveats. Across r/MagSafe and r/Truckers threads in our source pool, owners of higher-magnet-count mounts (20+ N55 magnets, ~3000gf+ pull) generally report no drops on normal roads, while weaker generic mounts repeatedly fail on potholes and speed bumps. A heavy case, PopSocket, or wallet attachment significantly increases the risk of detachment, so match the mount's stated pull force to your setup.