Chain line and chain wear...

On 24 Jun 2005 08:29:11 -0700, "Xyzzy"
<[email hidden]> wrote:

[snip]

Quoted message said:

PPS - I'm not cross chaining from the 53 very much... On my bike the
chainstays are so short I get pretty big angles going from the 39...
And yes, it is set up properly...

Thanks!

Dear Xyzzy,

It's unlikely that the "pretty big angles" caused by a
shorter-than-usual chainstay between the 39 tooth and the
larger rear cogs are a problem.

In fact, the shortness of the chainstays is unlikely to make
a visible difference in the angle of the chain.

To expand on an example from a recent thread about shifting
problems being attributed to short chainstays . . .

If chainstay distance (bottom-bracket-to-axle) shrinks only
13 mm (412 mm to 399 mm), and the largest-to-smallest rear
cog width is about 40 mm, then the maximum chain arc widens
from 5.545 degrees for the long 412 mm chainstay to 5.725
degrees for the short 399 mm chainstay--only 0.18 degrees:

5.725 degrees 5.545 degrees
| |
.__. highest gear | 40 mm
front_______________________.__. lowest gear |
0 399 412 mm

Here's a list that gives some idea of the degrees of chain
arc for various chainstay lengths with a rear cluster 40 mm
wide:

chain chain
stay arc
length degrees
412 5.545
402 5.682
392 5.826
382 5.978
372 6.137
362 6.305
352 6.483
342 6.671

Starting with a fairly normal 412 mm chainstay, we have to
shorten the chainstay about 70 mm (almost 3 inches) to
increase the maximum chain angle 1 degree.

If you have a midget chainstay only 302 mm long, the arc
increases 2 degrees to 7.545 degrees

But these are maximum cross-chaining arcs--if you don't do
much cross-chaining, then these tiny differences are muc
smaller.

The whole derailleur concept took off only after people
realized that chain alignment was nowhere near as crucial as
originally thought:

"The rest of the 1930's derailleurs suffered from the false
assumptions of the period: Chains have to be perfectly
aligned. (Although the wide, stiff chains of the period gave
some support to this theory, it is not true in general.)"

--Frank Berto, "The Dancing Chain," p. 142, 2nd edition

Whatever's wearing out your gears, it's not likely that the
short chainstay is the culprit.

Good luck,

Carl Fogel

Quoted message said:

2) In the big picture, what "ranking" does chain cleanliness, chain
line, sprocket size and torque applied to the chain affect wear? I have
read that the smaller sprockets wear faster due to having less teeth to
distribute the wear and because the chain has to flex more when it
passes over them... I am guessing that how hard you pedal affects
sprocket wear too... I just wonder if torque is an order of magnitude
more important to chain/sprocket wear than chain line, or vice versa...
Like, would you say the wear breakdown is torque 70%, sprocket size
15%, chain line $10% and cleanliness 5%?

Two fairly recent tests were done, one by Spicer:
http://www.sdearthtimes.com/et1199/et1199s13.html,

and another by Kyle and Berto:
http://www.ihpva.org/pubs/HP52.pdf

Both showed that chainline made a negligible difference in the
efficiency... ie it was too small to quantify. Kyle and Berto tested a
Shimano LX system (MTB triple) in the big/big and small/small combos,
so the chainline should have been more extreme than you are seeing.

Seems strange to me... if it's not inefficient, then why does it make
so much *noise*? I avoid the two largest cogs with the big ring, and
the two smallest with the small ring, because it just sounds like
something is wrong. I suppose it is possible that wear could be
accelerated when cross-chaining even though there aren't increased
mechanical losses... though I'm having a hard time imagining how that
could be.

Spicer also found that efficiency *increases* with higher chain tension
(with power held constant), instead of decreasing or staying constant
as I would expect. In fact, this effect was so great that it more than
offset the increased losses from using smaller cogs/rings (ie a 39/14
may be more efficient than the equivalent 53/19, or a compact 50/34
crank may be more efficient than a 53/39). Though Kyle and Berto's data
also shows a slight trend in the same direction, it is less convincing
than Spicer's.

Spicer ran a test with a clean unlubricated chain as well, and guess
what... the efficiency didn't go down! On that one I suspect that he
did not get the chain *completely* clean... just a *little* residual
lubrication would have lasted the duration of the test.

I hope that helps... even though the results are a bit
counter-intuitive.

-Ron Ruff

I just discovered that the Spicer test report can also be downloaded:

http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf

Power inefficiency (wear ) requires force (tension) and relative motion.

<[email hidden]> wrote in message
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Quoted message said:

Quoted message said:

Spicer also found that efficiency *increases* with higher chain tension
(with power held constant), instead of decreasing or staying constant
as I would expect.