Originally Posted by cny-bikeman

The combination of the large chainwheel in front and the smallest cog in back should only be ridden when you are going over 20mph. When riding your feet should be turning the pedals at least one revolution per second (60 rev's per minute - rpm). The reason for shifting is to keep that rate relatively constant. Between 70 and 90 is generally considerd ideal. Any lower is hard on your knees and equipment and inefficient.