[QUOTE=dddd;14686727]Are your tubes perhaps stretching greatly to fill the inside of the inflated tire? This would tug at the edges of the patch, so can eventually lead to a creeping failure of the bond surface.

Thanks for your comments. The tire size is an odd 28x1.75 or 700x45c but the lbs sales the closest tube 700x35-44c. It works but when I need to patch, I wonder if the tube expanding to fill the 45c circumference stretches past the amount the patch stretches and boom. If so, the same could be happening to op.