Funny you say that..... When I set out this morning, something was rubbing. I took the bike into the house and saw that the bead had acually popped over to the outside of the rim.... but the tube was still holding air! I knew the tire was not perfectly centered radially because there was a hop to it. I hadn't gotten around to fixing it yet. The tires can be pumped up to 115 psi and I pumped them up to just about that pressure before going to bed last night. I guess the bead popped without the tube letting go. I decided I'll only go to 100-105 from now on.