New bike inner tube problem. Help?

[cheerypie]

Hi, so I just changed my bike's inner tube last weekend and rode the bike for the first time yesterday. Now the bike tire is flat. There are no punctures in the tire itself. Does anyone know what's wrong? Why would the bike tire go flat after one use with the new inner tube?

 

[JamieM]

your tire pressure was too low or you installed the innertube incorrectly. This is known as a pinch flat. The innertube got caught in between the rim and the tire and got pinched