Tires not seating properly on rims. Challenge Parigi Roubaix tires, VO Raid rims. The rear tire lifted off and flatted on a downhill at 30+ mph. -holiday76 was riding it at the time. The front tire lifted off the bead just sitting in the garage. I figured out that both tubes were to large for the tire size (35mm+ vs. 28mm) and I re-applied both rim strips. Problem seems to have gone away. Maybe I can have -holiday76 do a test ride down the side of Mt. Diablo to make sure........