So I did this medium fast 24 miler the yesterday, late morning. In the early afternoon I felt like taking another ride. On my second ride something started feeling weired in my bike handling. I stopped and found my rear tire was going flat. First flat I've had on my new Calfee since I finally got it back from it's factory fix-up. I checked for anything that might be imbeded in the tire, found nothing, then changed the tube and pumped the tire up. Since it held air fine, I went on my ride and put around 20 more miles on my bike. I've got over 300 miles on her now.