Chain wear

father_jack
father_jack Posts: 3,509
edited September 2012 in Workshop
9 speed chain. I have park tool cc-3, it shows it is stretched, but I heard these ready made tools aren't exactly accurate.

I have also measured it. One measured 29.4mm from outer link pin center to outer link pin center

I have a couple of bikes, the other one which is quite new measures 29.2mm from outer link pin center to outer link pin center

Does 29.4mm sound like it's stretched?
Say... That's a nice bike..
Trax T700 with Lew Racing Pro VT-1 ;-)

Comments

  • pdw
    pdw Posts: 315
    Do you mean 25.4mm? 29.4mm is 1.16" which would be 16% stretch, which sounds unlikely.

    How many links are you measuring? You'll never get an accurate enough reading measuring just a single link. You should measure at least 10, preferrably more.

    Up to 0.5% stretch is OK. More than 1% is past the point of no return (you'll definitely need a new cassette too).
  • 10 links outer , 241 mm.

    That sound right?

    measuring a a brand new chain, 12 outer links is 293 mm

    ok I placed brand new chain alongside the old one, after 12 outer plates it was 1 or 2mm longer.
    Say... That's a nice bike..
    Trax T700 with Lew Racing Pro VT-1 ;-)
  • pdw
    pdw Posts: 315
    10 links outer , 241 mm.

    That sound right?

    Not really - that's 9.5 inches. Should be 10 inches plus the stretch.
    ok I placed brand new chain alongside the old one, after 12 outer plates it was 1 or 2mm longer.

    12 links = 12 inches = 304.8mm.

    1 / 304.8 = 0.003 = 0.3%

    So 1mm longer would be 0.3% stretch (i.e. fine), 2mm longer would be 0.6% (i.e. time to change).
  • sungod
    sungod Posts: 16,845
    using an imperial ruler, with the chain taut...

    rivets on an unworn chain will line up with 0" and 12" marks

    on a worn chain, the rivets will measure further apart

    if the excess is < 1/16" it's ok
    if >= 1/16" replace chain before it gets much worse
    if it gets to 1/8" the cassette is probably trashed
    my bike - faster than god's and twice as shiny