MTB had a front flat this morning. couldn't find the cause by eye balling the outside of the tire. used some soapy water to make a bubble & found the puncture in the tube. marked it w grease pencil but then sanded it & patched it. found the minuscule offending wire spec inside the tire & flicked it w/ my fingernail. wasn't big enough to grab. patch holds great & I had a nice ride