Chain skipping

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

Mark South said:

Quoted message said:

It's mainly because they're larger (on a road bike at
least). I think being at the *front* might make a
difference as well, though I don't understand why.

The pressure load at the front is shared over many more
teeth. The wear is a nonlinear function of the pressure
on the teeth.

Yes but what about when the chainring happens to be
*smaller* than the largest rear sprockets (as in the case
with some triple inner chainrings)? I think they still
wear slower in that case as well.

Well, ride around for a few months in your 22x34 gear,
measure the wear and report back :-)

Quoted message said:

Quoted message said:

Quoted message said:

> Are sprockets softer?

Nope, usually harder!

Depends. If they are hard, they are generally case
hardened. Once the hardened layer wears through, the
softer metal beneath wears very rapidly.

Chainrings are often aluminium. Rear sprockets are usually
steel. Just have a go at filing them if you doubt which
are harder.

A. Case-hardened aluminium can be way harder than mild
steel.
B. Filing is a very poor way to judge hardness - titanium,
for example, cannot be made much harder (without being
ridiculously brittle) than around 48-50 Rc, but filing it
is a pain because it work-hardens under the file and the
soft bits that do go into the file clog the teeth. This
is what Rockwell gauges are for.
C. Actual hardness does relate very well to wear
resistance though.
--
Mark South Citizen of the World, Denizen of the Net <<Tiens!
Ce poulet a une grenade!

"Just zis Guy, you know?" <[email hidden]> wrote in message
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Quoted message said:

On Tue, 18 May 2004 19:03:37 +0100, "Pete Biggs"
<[email hidden]> wrote in message <2gv1f7F705jvU1@uni-
berlin.de>:

Quoted message said:

Chainrings are often aluminium. Rear sprockets are
usually steel. Just have a go at filing them if you doubt
which are harder.

Maybe wear particles become embedded in the soft
material, causing it to wear the chain rather than the
chain to wear it?

Chain steel is probably the hardest stuff on your bike apart
possibly from the ball bearings. Chains as a consequence can
be brittle - most of us have seen chain plates fail
catastrophically.

But frankly, it's less work to replace one's chain every
3000 km than it is to try to work out what the wear
patterns are....
--
Mark South Citizen of the World, Denizen of the Net <<Tiens!
Ce poulet a une grenade!

In article said:

Mark South said:

Quoted message said:

It's mainly because they're larger (on a road bike at
least). I think being at the *front* might make a
difference as well, though I don't understand why.

The pressure load at the front is shared over many more
teeth. The wear is a nonlinear function of the pressure
on the teeth.

Yes but what about when the chainring happens to be
*smaller* than the largest rear sprockets (as in the case
with some triple inner chainrings)? I think they still wear
slower in that case as well.

Probably used less in those cases.

In article said:

Mark South said:

Quoted message said:

It's mainly because they're larger (on a road bike at
least). I think being at the *front* might make a
difference as well, though I don't understand why.

The pressure load at the front is shared over many more
teeth. The wear is a nonlinear function of the pressure
on the teeth.

Yes but what about when the chainring happens to be
*smaller* than the largest rear sprockets (as in the case
with some triple inner chainrings)? I think they still wear
slower in that case as well.

Probably used less in those cases.

Mark South said:

A. Case-hardened aluminium can be way harder than mild
steel.
B. Filing is a very poor way to judge hardness - titanium,
for example, cannot be made much harder (without being
ridiculously brittle) than around 48-50 Rc, but filing
it is a pain because it work-hardens under the file and
the soft bits that do go into the file clog the teeth.
This is what Rockwell gauges are for. C. Actual
hardness does relate very well to wear resistance
though.

Thanks for the info. Which make/model chainrings use case-
hardened aluminium?

~PB

Mark South said:

B. Filing is a very poor way to judge hardness - titanium,
for example, cannot be made much harder (without being
ridiculously brittle) than around 48-50 Rc, but filing
it is a pain because it work-hardens under the file and
the soft bits that do go into the file clog the teeth.

Why is steel that is hardened and very hard, like that used
in tools, much more difficult to file or saw than mild steel
(which in turn is more difficult to file than typical
aluminium alloys used on bikes)?

What is so different in principle about the action of a
chain on a sprocket than a that of a file?

~PB

Pete Biggs said:

What is so different in principle about the action of a
chain on a sprocket than a that of a file?

The fact that wear particles will embed in the softer
material and cause wear on the harder (just as white-metal
bearings can wear hardened steel crankshafts). But I don't
necessarily think that's what's happening here.

--
Guy
===
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When I first saw this thread's title, I wondered if it was
an extreme sport for the school playground!

I was sure it meant there was a set of 8yo girlies who were
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"Pete Biggs" <[email hidden]> wrote in message
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Quoted message said:

Mark South said:

A. Case-hardened aluminium can be way harder than mild
steel.
B. Filing is a very poor way to judge hardness -
titanium, for example, cannot be made much harder
(without being ridiculously brittle) than around 48-
50 Rc, but filing it is a pain because it work-
hardens under the file and the soft bits that do go
into the file clog the teeth. This is what Rockwell
gauges are for. C. Actual hardness does relate very
well to wear resistance though.

Thanks for the info. Which make/model chainrings use case-
hardened aluminium?

I'd expect any half-decent industrial aluminium bits to be
correctly hardened for their application. Mild aluminium
chainrings probably wouldn't last more than about 5 miles
before the teeth wore off.
--
Mark South Citizen of the World, Denizen of the Net <<Tiens!
Ce poulet a une grenade!

"Pete Biggs" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

Mark South said:

B. Filing is a very poor way to judge hardness -
titanium, for example, cannot be made much harder
(without being ridiculously brittle) than around 48-
50 Rc, but filing it is a pain because it work-
hardens under the file and the soft bits that do go
into the file clog the teeth.

Why is steel that is hardened and very hard, like that
used in tools, much more difficult to file or saw than
mild steel (which in turn is more difficult to file than
typical aluminium alloys used on bikes)?

Well, tools are made of tool steels which are often hardened
about as far as they will go. 64-66 Rc is not uncommon. At
that hardness they are very brittle and do not bend before
breaking. Many tools will shatter like glass when dropped on
a workshop floor.

Basically, the harder the material the harder it is to file.
(But as I said, there are softer materials that are also a
pain to file.)

It also depends on how hard your files are. You need very
good quality files to make an impression on a well-hardened
piece of carbon steel.

For example, I have a knife blade that appears to be
hardened to about 61-63 Rc (not uncommon for decent knives)
and some medium quality files that are rated as 62-64 Rc. As
you can imagine, it's a hell of a lot of work to get the
files to make any mark at all on the blade and the files
wear pretty quickly at the work.

Quoted message said:

What is so different in principle about the action of a
chain on a sprocket than a that of a file?

The pressure load is qualitatively even greater. A file or
saw concentrates all the force onto a tooth or two that then
presses impressively hard on the piece being worked.

A chain is designed to spread the load evenly over a
reasonable tooth area, and over several teeth at a time. The
irony is that as the metallurgy improves, the gains are
squandered on using narrower and smaller sprockets and
chains....
--
Mark South Citizen of the World, Denizen of the Net <<Tiens!
Ce poulet a une grenade!