On Feb 21, 8:18*am, Jeff Liebermann wrote:
On Thu, 21 Feb 2013 18:35:49 +1100, James
wrote:

I just came across this;
http://www.cantitoeroad.com/docs/con...ns_Stretch.pdf

I wish you wouldn't post interesting items just before I go to sleep.

I can't see whether the stretch was plastic or elastic. *The length
doesn't appear to have been measured again with a 10kg load.

Yeah, that's what I was thinking. *Are they measuring metal
deformation or are they measuring a spring.

If it's plastic ... ouch! *I hope it's not. *I don't think it can be..

It's not. *My guess(tm) is that they took brand new chains, out of the
box, and ran the test. *No breakin and a 10Kg preload is probably not
sufficient. *The new chains will still have microscopic stamping and
machining defects that need to be worked out before such a test.

0.5% under 150 kg load. *39 tooth CR has a radius of about 79mm, and
175mm cranks gives a force multiplier of 2.2. *A 75kg dude could easily
stretch a stretchy chain 0.5% just by standing on the pedals.

Ok, let's grind the numbers. *The worst chain (KMC X 10 SL Gold)
failed with a total stretch of 2.15mm @ 150Kg. *The test chains were
31 links long or about:
* 31 / 24 * 1ft * 30.48cm/ft = 39cm
Sanity check... the percent stretch should be:
* 2.15 / 39 * 100% = 5.5%
which agrees with the chart of test data.

According to conventional wisdom, a chain should be replaced when it
stretches 1/16" out of 24 links or 1ft. *That:
* 0.0625" / 12" * 100% = 0.52%

2% stretch is recommended as the limit by Wipperman (but perhaps not
strictly apply with silly small teeth on modern multi-sprocket
bikes). For 99% of the time all the chains will be below that level
of elongation taking both wear and active load into account.


So, by conventional wisdom, ALL the chains in the test should have
been immediately tossed because they had stretched up to 10 times the
acceptable limit for chain stretch. *Something is wrong, very wrong
(hopefully not with my logic because I'm almost asleep at the
keyboard).

I'll not be loading the chain of my "racing" bike with a consistent
load of 150kg anytime soon.

It's more realistic to measure the load at which one can sustain (for
at least 10 minutes) with purely nasal breathing.