Like the human skin, tires bump up against objects and they can be cut.  The difference is we heal, they don't.  A ruptured to flat tire is proof positive that the tire has been damaged and needs to be replaced.  The truly dangerous tire is the one that has had the outer layer of rubber skin cut to the cord but is still inflated (see our photo).  A deep cut weakens the tire and makes it vulnerable to a possible blow out because the cords (belts) are not properly supported.  Make sure all your tires are inspected inside and out before heading out for your summer vacation.  Have you ever experienced a tire blow out?