Chain wear

father_jack

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?

pdw

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).

father_jack

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.

pdw

Father Jack wrote:

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

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