Chain Length

Mystique Posts: 342
edited May 2008 in Road beginners

Is there some kind of formula/ rule for Chain Length?? I need to fit a new chain on my roadie (compact chainset, 12-24 cassette) & want to get it right first time...for once :wink:



  • keef66
    keef66 Posts: 13,123
    Although you probably would never do it, the theory is that you set the chain length so you can just use the largest chainring and the largest rear sprocket.
  • Mystique
    Mystique Posts: 342
    That make a lot of sense - Thanks Keef.
  • dennisn
    dennisn Posts: 10,601
    In theory and usually in practice you also need to be able to shift onto the smallest
    front ring and the smallest rear cog without an excess of chain to clog things up.
    As keef66 says, you would not normally use biggest ring-biggest rear cog, it is also
    true of smallest ring-smallest cog not being used normally. However, on the off chance that you do shift into one of these two combinations things need to work or chain and or
    rear mech binding can occur and that's not good. Chain length is really something to pay attention to. Get some help if you are not sure. Chain is cheap but rear mechs are not.

    Dennis Noward
  • Zendog1
    Zendog1 Posts: 816
    The easiest way is to cut it to the same number of links as the old chain - lay them side by side on a bit of clean flat ground. The old chain will be a bit longer but only a small fraction of a complete link.


    With the chain on the largest chainring, smallest cog cut the chain until the jockey wheels (on the rear derailier|) align vercically - straight up and down. A nail to hold the two cut ends together helps in judging this. This works for a standard double - not 100% sure about a compact (never owned one).