The smallest sprocket is usually the driver or input sprocket. As the chain enters and exits, it rises and falls as each pitch engages and disengages the sprockets. This movement, called chordal action, causes chain-speed variations (drive roughness) that may be objectionable in some applications. These variations can normally be minimized by increasing the size of the sprockets. To minimize the negative effects of chordal action, the following are suggested guidelines for the minimum number of teeth in the smallest sprockets:

  • Slow speed drive (drip type lubrication) – 12 teeth
  • Medium speed drive (oil bath type lubrication) – 17 teeth
  • High speed drive (pumped lubrication) – 25 teeth