I am just 15, I have a dyno bike with back brakes, no front ones, but back pedal brakes which is kind of peculiar sounding. The problem is with the back brake. Now I don't know anything about bikes, I couldn't even tell you what a crank is. The brake pads have constantly been rubbing against my back tire slowing me down increibly. I am so used to it now that I can't even tell when it is rubbing against it or not. It's been going on for about 2 years. I took it to the bike shop near me, and they said nothing was wrong with it which was completely stupid. If you hold up the back of the bike and pedal for some seconds and stop, the tire will stop moving within 3 seconds. I am completely desperate, there is nowhere to take my bike, I know nothiung about bikes, and my life is biking. I need help really bad.