Knew I was losing a few PSI in one of my rear tires. Finally found a skinny nail in the middle of the tread, right next to one of the wear bars. Son of a beotch! I haven't had a nail in a tire in 8 years, I guess I was due. The local tire shop charges $15 to patch it, hopefully they don't care the tire is a F1 Supercar. I don't go over 100mph, so not worried about having a patch.