Roxie, the casing is the body of the tyre ( the sides) my own wife kerbs her car tyres not once but many many times, this cannot do the body of the tyre any good, I have on many journeys seen Eggs on tyres ( A bulge in the tyre walls) I have had these on the HGVs that I used to drive, when they blew, you knew it, I always check my tyres on a visual basis daily & always check the pressures weekly ( No, I'm not bull shting) I value my wife's & my self's life & its the likes of bad tyres that can end your life quickly