Here is a real tunnel flip = not quite as smooth as the SLS commercial.

too bad it is Jeremy,,,

YouTube - Clarkson - Tunnel Loop

 

I was hoping the car would ride the outside wall like a plane in a 90 degree bank. With enough speed it might be possible. As kids we had electric Hot Wheels cars called sizzlers and they would ride the vertical wall of a huge round sink outside the bathrooms at school.