Originally Posted by
Andrew R Stewart
Another subtle flat cause we see more often than years ago is the wire puncture. The wire (from auto tire casings I think) get picked up in the tire and in time work their way through the casing to prick the tube. These holes are generally able to be seen, bubble track wise. But the wire can be hard to feel for, unless you reverse the direction you run your fingers along the inside of the tire. The wire is often at an angle that "lays flat" if brushed one way but will become "upright" if brushed the other way.
Having caught a few wires and tiny chips of glass with my fingertips while checking for embedded debris, I'll usually check with a microfibre cloth first to reduce the chance of lacerations. Also just work around the outside of the tyre pinching the tread so any small cut opens up, sometimes revealing a sharp or pointy thing in its depth - these are the ones that remain hidden in the tread when you feel for them, but manage to cut the tube when you ride with them.