Chain measurement the dark art

Kingsmill1 Posts: 103
edited December 2012 in Road beginners
I'm looking to replace my chain on my allez sport as its stretched I'm going for a direct replacement which is a kmc x9 chain now the next bit is how can I insure I measure it correctly and not totally bugger the job up. Can I just measure off the old chain or would this cause problems as its stretched a little. I'm a total bike mechanic novice so please excuse the dumb question but want to learn how to do it myself rather than pay £8 a time to my lbs.
Giant TCR Comp 2
Specialized Allez Sport


  • 16mm
    16mm Posts: 545
    Just measure against your current chain. You want the same number of links, but you old one won't be so stretched that you can't measure side by side.
  • Mad_Malx
    Mad_Malx Posts: 5,005
    ... so lie them down next to each other (on something clean) and kink the old one slightly so that the links stay roughly aligned.

    Edit - and make sure you have the outside link at one end and end up with an inside link at the other.
  • sungod
    sungod Posts: 16,551
    before you remove the old chain, use a 12 inch ruler and measure the distance from one of the pins to the pin that will now be slightly past the 12 inch mark - see how here...

    if it's less than 1/16" past the mark, chain is ok

    if it's reached 1/16" but is still less than 1/8" past, it's time to change the chain

    if it's 1/8" or beyond then the old chain has worn so far that it has probably damaged the cassette, in this case you'll find a new chain may slip on the old cassette or you'll get accelerated chain wear - if the chain has reached this point, you may as well run it a while longer because when you change it you'll need to change the casssette (which costs a lot more)

    moral - check the chain every few weeks, otherwise the cassette may be worn out much sooner than it should be
    my bike - faster than god's and twice as shiny
  • damov2
    damov2 Posts: 66
    It's as simple as counting the pitches, just count each pin (pitch) do the same for the new chain and your sorted.
  • Thanks for the advice I got a kmc chain checker off flee bay chain is still ok for the moment
    Giant TCR Comp 2
    Specialized Allez Sport
  • simon_e
    simon_e Posts: 1,706
    damov2 wrote:
    It's as simple as counting the pitches, just count each pin (pitch) do the same for the new chain and your sorted.
    Yes - count pins, don't measure.

    As for wear, I would err on the side of caution and change it sooner rather than later.
    Aspire not to have more, but to be more.