I had a flat that sounds annoying but wasn't. I hadn't ridden my Lemond with 650b tires in a long time. I grabbed it to take it to class today, and the rear was flat. It's the tube I patched earlier this year. Failure? I took the tube out and didn't find a leak. The good news is that 1. I had my bike stand ready to go and enough space to use it in, 2. the tires are loose and easy to remove and replace, 3. it's easy to put in 50 psi with a floor pump. I didn't even get my hands very dirty. The tire seems to be holding air. Maybe it's a very slow leak at the patch. No big deal with low-pressure tires.