Coldest day so far this year. Thirty degrees at start was in full winter gear. At the 9 mile mark had a flat! It was a moonless morning and could not see much. C02 did not work. Blew two cartriges. They would just expell contents when engaged. In the end they would not have helped because the hole in the tube was too big. Rode home standing to keep weight on front wheel and walked some. The question is calories burned