I am first time bicycle buyer and I'm starting my search for a new bicycle and I don't understand how the stores mention that a bicycle is for example a "single" speed. I always thought a bicycle can go as fast as your feet can pedal. Now, a vehicle, it would make sense if a car dealer would say, oh "that car can go up to 150mph" or something in that manner.. but on a bicycle? Speed is your feet on the pedal right?