Things that I recently learned about bike tires:

1. A tire is made up of an outer shell and an inner tube.


2. When and if you have a flat, it's typically because the inner tube has been punctured.


3. It is important to note, however, that all bike tires "breathe" and as such, it is typical to need to pump up mountain bike tires every few days and road bikes even more often


4. A thorn or other sharp object may puncture the outside "tire" as well as the inner "tube" since the inflated tube presses up against the inside wall of the tire. In which case it will be necessary to replace the tube, even if you only bought it a few days before after incorrectly buying a bike pump thinking that the tire just needed air.

I hope that this information proves didactic for someone.