On one-piece rim brake pads, I've always wondered how deep in the steel support bar is. Take a look at this one, cut away after about 4,000 miles of urban stop-and-go riding:
Changed just in time. In this case, an Avid pad, the casting seam lines up with the support. I don't know if that's the case with other brands. Maybe probing with a pushpin is a way of finding the safe point. The manufacturers really ought to put a mark on the outside.
You got to be very careful if you don't know where you're going, because you might not get there.
