Chain Selection

Overview

  • Two standard sizes in FIRST
    • ANSI 25: 1/4" pitch, 115 lb working load (McMaster-Carr)
    • ANSI 35: 3/8" pitch, 269 lb working load (McMaster-Carr)
  • Chain stretches/wears over time
    • If lengthening is significant chain will skip teeth
      • If this happens, chain will need to be tensioned
  • Higher tension causes chain lengthening to occur faster
  • If large sprockets are used with 35 chain, tensioning can be avoided
    • If tensioning is not used, it is important to space wheels such that a whole number of chain links are need to span the distance
    • The distance between wheels should be a multiple of the chain pitch
      • If the distance between two wheels is 15.5" when using 35 chain (0.375" pitch), 41.33 links are needs, so 42 links will be used, which totals 15.75". There will now be 0.25" of slack which is enough for the chain to skip teeth and a tensioning system will be needed to correct this, defeating the purpose of using thick chain and large sprockets. It would be better to use a wheel spacing of 15.375" or 15.75" so a whole number of chain links are needed.