listen, i am a competitive biker with alott of experience- and i hate getting a flat. If you think your bike is not working properly, then stop on the side of a trail, road ect. and check your tires. if the tire does'nt have any air or the tire is losing air, you have a flat. If the tire is losing air then it is possible to fix using a repair kit, but is mostly eaiser to walk it home. now if the tire is completely out of air then search for where you think it might be leaking Ex: glass, screw, or simply a loose connection. Next time you happen to be by a repair shop, drop it off and ask them to patch it up or get a new tire.