After a scary moment in a corner, I was forced to examine the front tire more closely. It had plenty of tread, but there was some evidence of cracks in places. It was a Metzeler from long ago, and it was time for a replacement. I settled on an IRC. Upon removal of the tire, I discovered that it had no rim strip, and the tube had deformed into the rim with perfect rust circles where it met the spoke nipples! A rim strip and a new tube was quickly acquired and installed.