Darnest thing - I discovered a flat on the rear wheel of my Specialized Roubaix yesterday before my ride, or planned ride.
I put in a new tube and pumped her up. The tire is riding out of the rim at the valve hole. I didn't notice it, so I had 120 lbs. of pressure before I realized the tube was coming out of the tire. Now I can't get the tire to stay down in the wheel. Can't figure it out- never had this occur before with the same wheel and tire.
It's as if there's an extra layer or two of tube there at the valve, keeping the tire from seating down in the wheel.