I have BOntrager Hard Case and when my shoe got caught in my wheel and ripped my fender off and ground it into the tire... it still held air. Should have been slashed to ribbons. (I did replace the tire, though, because it had been pretty shredded... just not past the top layer). The only flat I've had in a few thousand miles was last week when the tube failed... oh, and trying to put the tube back in when I replaced the tire. THey are *hard* to get on, tho' I think I might have figred out the secret (to put the tube in with *no air*).