On 9/15/2017 5:48 AM, John B. wrote:

I've been thinking about chain wear, sometimes called chain stretch,
and have done a bit of research on the subject.

One method is to lay the chain on a flat surface and measure the wear
over, perhaps 12 inches of chain length, from the head of one pin to
another. But modern multi speed chains are a bit more complex then the
old fashioned chains and the rollers on a modern chain are not
supported by the pins but by protrusions on the inner surface of the
inner links thus does the distance from roller to roller relate to
distance from pin to pin?

Another method is to ignore the pin to pin distance and simply measure
the roller to roller distance using a chain gauge. But I have also
read that when comparing roller to roller measurement to pin to pin
measurement there is not necessarily a correlation, or in other words
a pin to pin measurement might show one thing while the roller to
roller might show a totally different wear pattern. In addition I read
that in at least one case the roller to roller wear was not constant
and varied from place to place in the length of the chain

Brandt, I believe, wrote a treatise on chain measuring gauges and
argued that nearly all of them gave an incorrect figure for wear, or
perhaps, did it the wrong way.

So the question is what is the best system to use to avoid unnecessary
sprocket wear, assuming that sprockets cost more and are more trouble
to change than chains.

There seems to be three options. One, to use a ruler and measure from
pin to pin. Two to use a chain tool and measure from roller to roller.
Or three, to use some combination of the two.

Or perhaps there is a fourth - ignore the whole thing as a tempest in
a tea pot :-)

I vote for "tempest in a tea pot."

I understand that measuring pin to pin might give slightly different
results than measuring using a chain gauge. But ISTM the difference
must be minimal. If (say) your standard for chain replacement is 1/2%,
and pin-to-pin gives 0.6% while chain gauge gave just under 0.5%,
wouldn't it usually be sensible to replace the chain anyway?

BTW, as Andrew said, I think it's worth while to put tension on the
chain, not lay it out on a table. If the chain's off, perhaps hanging it
from a nail would do. I measure mine on the bike and apply tension by
blocking the rear wheel while applying a little force to the cranks.

--
- Frank Krygowski