I went out yesterday morning all ready to ride to work. Added air to one tire then went while adding air to the back tire the stem broke. The tire went flat. I had a new tube so I tried changing it. Since I have only taken a class on changing flats and tried it there I do not have much faith in my skill. Well I went about undoing the back brake and taking off the tire. After changing out the tube I could not seat the tire correctly around the stem area. So I put the bike on the bike rack on the car and tire in the back seat. I took it to a bike kitchen, where the guy showed my that the stopper on the stem needed to be taken off the tube before putting on the tube. I did not realize that piece came attached to the tube. I thought that the guy in the bike store just added that piece. Anyway he let me do the work and I finished up the changing of the flat. I have more faith in my skills now!!