Chain skipping on large chain ring.

Ron Ruff wrote:


[...] and the chainring isn't worn.


I'm not so sure, or, more strongly, I think it's worn out.

I've taken a chain ring off my bike that had its teeth worn into an
assymetrical shape similar to the one shown, although not so extreme.
Some areas of the ring were worn more than others. The teeth were
symmetrical when new. The symptom I had was that with a new chain it
would run very noisily under heavy load (climbing).


Either the chainring is defective,


This isn't a new ring. I can't believe that it did this when the bike
was new, or Mike would have mentioned it.


or it wasn't designed to go backward in the first place
(or both). I'm more interested in how it is performing in the forward
direction: What does "hooking action" mean? Is noisier in the large
ring vs. the small, and how would you describe the sound? When you
pedal backward, does it ride up in all the gears, or only when
cross-chained?



-- Andy Heninger

Ron Ruff writes:

Well, we're still not to the bottom of the phenomenon.

Maybe we are getting close...

The OP wrote in his original post "The big ring, however, has a bit
of hooking action going on when pedalling forwards, and if I pedal
backwards the chain rides up the teeth every once in a while and
then plops back down where it is supposed to be."

Pedaling backwards with this odd tooth form should cause tooth
climbing. That is not a reasonable test of the chain in normal use.

So, except for the "bit of hooking action", which I'd like to know
more about, the problem is when pedaling backwards. Since the teeth
on the large ring are cut in such an extreme way, isn't it possible
that it simply doesn't work well going backwards?

As I mentioned, this is not a worn CW but it has a saw tooth profile
for some imagined benefit as seen by Cannondale. The chain skip
occurrs pedaling forward if I understood it correctly. If that is not
the case then this whole episode was a misunderstanding for me and
there is and was no problem.

The chain is good, and the chainring isn't worn. Either the
chainring is defective, or it wasn't designed to go backward in the
first place (or both). I'm more interested in how it is performing
in the forward direction: What does "hooking action" mean? Is
noisier in the large ring vs. the small, and how would you describe
the sound? When you pedal backward, does it ride up in all the
gears, or only when cross-chained?

We don't need no steenkin backpedaling. I want to know the
circumstances under which the chain skips over the CW under forward
pedaling load.

Jobst Brandt

Andy Heninger wrote:
[...] and the chainring isn't worn.


I'm not so sure, or, more strongly, I think it's worn out.


The OP stated that the bike only had 4,000 miles and he basically never
used the large ring. His old chain was not excessively worn either, so
if the ring is weird, it must have been made that way.

The teeth were symmetrical when new.

My Dura Ace large ring came new with hooked teeth and machining,
supposedly to improve shifting. I don't know how common this is on
chainrings these days, but the machining on the Cannondale ring's teeth
looks even more extreme. My small DA ring is symetrical.


I can't believe that it did this when the bike
was new, or Mike would have mentioned it.


Something about the new chain made it worse, but if the chain is ok...
then it must be the ring... and if the ring is barely used, then...

The OP wrote in his original post "The big ring, however, has a bit
of hooking action going on when pedalling forwards, and if I pedal
backwards the chain rides up the teeth every once in a while and
then plops back down where it is supposed to be."

Pedaling backwards with this odd tooth form should cause tooth
climbing. That is not a reasonable test of the chain in normal use.

Exactly, but that was the only significant problem ever reported by the
original poster. Therefore things are actually behaving normally and
the OP shouldn't replace any components but just enjoy riding his bike.
My guess is that the riding up while pedaling backwards may be the
result of a combination of rather short chainstays, a rear derailer
(sp. by Sheldon) jockey wheel cage that may be slightly askew (aimed
slightly inward), and a new chain that's stiffer laterally and has less
rounded edges on the side plates. But since normal riding involves
forward rather than backward pedaling, I wouldn't worry about it.

We don't need no steenkin backpedaling. I want to know the
circumstances under which the chain skips over the CW under forward
pedaling load.

The original poster never reported any such skipping under normal
pedaling - only the riding up behavior when pedaling backward.

Ron Ruff wrote:
Andy Heninger wrote:

[...] and the chainring isn't worn.


I'm not so sure, or, more strongly, I think it's worn out.



The OP stated that the bike only had 4,000 miles and he basically never
used the large ring. His old chain was not excessively worn either, so
if the ring is weird, it must have been made that way.


The original poster also said

I ride 99% of the time in the small ring. I can only think of 3 or 4
times, since I bought the bike, where I have used the big ring.

Sorry, I overlooked this before. So the problem remains a mystery. I
had taken the 4000 miles to be for the chain, not the ring, which could
have seen many chains in its lifetime.

-- Andy Heninger

wrote:
Marvin Meredith writes:

SNIP

As I've said, your chainrings are atypical - I see *no* rings like
that at the LBS where I work and many, many with sharper ramps like
the one of Carl Fogel's I keep dragging up as a convenient example.
I believe this is related to the amount of care taken replacing worn
chains.

Maybe in your circle of riders, but for mine it is typical.

In which case your circle of riders is still not typical of the average
cyclist. I think I can claim to see more "average cyclists" than you
in a day...

We ride
bike to ride and don't mind riding on less than new components.
Carl's CW has no teeth. Those are only stubs of teeth that could not
drive a new chain.

Yes, and that chainring got like that under relatively low mileage. It
is entirely possible for a chainring to be worn to the point of
slipping with low mileage, this is my point.

This might be a long example, so bear with me:

Assume we have a new chain and chainwheel. As the chain rolls on to
the chainwheel, each roller will come into contact at a certain
point. If the chain is the correct pitch, it will contact at the
same point as the previous roller, which should be the base of the
tooth profile, and all is well.

Now the chain wears faster than the chainwheel, so in due time we
have a worn chain and new chainwheel. Now when each roller engages
it is slightly further from the previous roller than it should be,
so it starts taking load and wearing some way up the tooth profile.

That assumption of wear rate is immaterial because the pitch of the CW
remains constant while its pressure pocket in its teeth increases in
height above the base circle as chain pitch increases from wear.

Assume we don't replace either, and continue riding. The worn chain on
the worn chainring is now running steadily higher on the tooth profile,
and as it wears there will be less and less teeth taking any load so
the wear gets faster. The profile of the tooth is gaining a relatively
straight ramp until it wears right to the top of the tooth, sharpening
the top of the tooth quite nicely and slipping under any load at all.

From elastic considerations only the first few teeth of the CW bear
any significant load. You can test this by lifting the chain off the
CW starting at its exit end.

If, on the other hand, the chainring never gets used with an
appreciably worn chain, the wear stays low on the tooth profile. It
still moves up slightly as shown by your extreme example, but by no
means as fast as with a worn chain.

So, in conclusion, the wear moves up the tooth faster with a worn
chain, and the wear is faster with a worn chain.

Yes??? and now what?

Just as an aside, the difference in wear between heavily and
lightly loaded chainring teeth is quite a good indicator of riding
style - big difference = stomper, small difference = spinner. I
regularly impress easily impressed customers with this particular
sleight of hand :-).

I think you should explain how you believe this comes to pass.

It's very simple, more load at a given point on the chainwheel equals
more wear. Worn chains don't spread the load anywhere near as evenly
between teeth and therefore wear chainrings faster. I don't see why
this is contentious.

It isn't, but you seem to suggest one should ride the lowest gear
possible for the benefit of bicycle components, modifying one's riding
to something other than what might come naturally? I believe the
bicycle is the riders servant, not the converse. Besides, this does
not affect the problem at hand.

Actually I do think (and practise) that, but I'm pretty sure I didn't
advise it in this thread :-)

My worn chainring has about 100,000 miles on it, that is, it was in
use for about 10 years and looks much like many others I have seen
that were not changed out by equipment fanatics.

I'll say it again, if someone is careful about changing their chain
they can indeed expect their chainrings to last for ludicrous numbers
of miles. If they aren't, well, 10,000 miles is a closer par for the
course.

So what is wrong with riding a CW for 10x as long by replacing the chain
at 0.5-1.0% chain wear?

This would be my entire point - not everyone does that. Hence
chainrings wear out, and wear out quickly.

Let's get back to the failure analysis at hand. I find it mysterious.
In fact every time I read of chains jumping over CW's in this forum, I
wonder how it is done, not having had this occur on my bicycle or
those of my riding companions since I got my first derailleur bicycle
in the 1950's.

Here is how it is done: try *not* replacing your chain religiously,
like an awful lot of people don't. Then you'll wear your chainring out
within about 10,000 miles, and hey presto, it'll start slipping.

Yes, I know, that's a silly thing to do, but I'm telling you it
happens. If someone comes into the shop and tells me their gears are
slipping despite a new chain and sprockets, I look straight at their
chainring for wear, and at least 95% of the time I'm right. Over the
past three years that adds up to a pretty big pile of experimental
evidence, not to mention worn out chainrings.

Okay, I think this is a big enough diversion just to argue about
whether chainrings wear out or not. I'll go back to scratching my head
about the OP's problem now.

Xyzzy wrote:

That would be handy, actually. Then we can see the wear on all the
teeth much more clearly.


http://www.teamendorphin.com/jpg/53.jpg
http://www.teamendorphin.com/jpg/39.jpg

I found out last night the spider on the crankset is a regular 130mm
BCD deal, so I will most likely just order new chain rings... I really
don't want to destroy my new chain or my cassettes... My guess is
Cannondale may have tried a little too hard to shave weight on these
rings and either didn't use enough material or used a material that is
too soft...

The chain ring bolts are pretty wild too... They thread into the 39,
not into little nuts like most I have seen...

If I continue using the 39 for a few rides do you think I will harm
anything? It will take me a week or so to order and receive new
rings... I don't have a backup bike to ride in the meantime... I'll
most likely put 300 or so miles on the bike before the new stuff comes
in...

Finally, apparently I have a lot of choices for replacements... Are
there any particular ones I should consider? So far I have seen Campy
rings, FSA rings and TA rings... I'll most likely get 53/39 sizes
although I am very tempted to get 52/42, since I could use a tiny bit
more top end on the small ring... Going from a 39 to a 42 would give me
one more gear higher across the board...

BTW, I do know I must match the rings for shifting purposes... IOW, the
53 for the 39 is different than the 53 for the 42...

No, manufacturers tell you to match sets but we haven't seen
any advantage.

You write " chain ring bolts . . . thread into the 39" but
your photo doesn't show that at all . ?? Could you clarify?

Except for a few fast-wearing brands (Vuelta) any 130mm
chainring will do. More expensive rings can be longer
wearing but there is not always a correlation.

Your concern about those soft aluminum rings wearing your
steel chain or cassette cogs is unfounded.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

You write " chain ring bolts . . . thread into the 39" but
your photo doesn't show that at all . ?? Could you clarify?

The chain ring bolt holes on the 39 are threaded... The chain ring
bolts pass through the 53 and then the spider and are then threaded
into the 39... I've never seen a setup like this before but maybe it is
common?

If it would help I can remove the rings again and photograph one of the
bolts...

--
Mike (Xyzzy)

In article .com,
says...
The way to avoid this is to religiously change chain every time the
faintest bit of stretch occurs. That way the rollers are always
sitting in the base of the tooth. The fact that only Jobst can report
chainrings that are worn but still with symmetric teeth suggests that
the vast majority of us aren't as careful about chain replacement as we
should be...

but Jobst said he rotates the chainring (as well as changing chains) to
spread the wear around the ring. Does he reverse the ring as well to get
symmetric wear? I wouldn't do this as my rings have shifting profiles
and I'd be happy to say I've worn out a chainring anyway. My touring
bike's chainring looks a bit worn - probably a lot less than half way to
Carl's example at 17,000 Km.

Bruce G

Bruce Graham writes:

The way to avoid this is to religiously change chain every time the
faintest bit of stretch occurs. That way the rollers are always
sitting in the base of the tooth. The fact that only Jobst can
report chainrings that are worn but still with symmetric teeth
suggests that the vast majority of us aren't as careful about chain
replacement as we should be...

but Jobst said he rotates the chainring (as well as changing chains)
to spread the wear around the ring. Does he reverse the ring as
well to get symmetric wear? I wouldn't do this as my rings have
shifting profiles and I'd be happy to say I've worn out a chainring
anyway. My touring bike's chainring looks a bit worn - probably a
lot less than half way to Carl's example at 17,000 Km.

There being 5-bolts on the kind of CW I use, rotating them is an
imprecise art since 90 degrees is the desired rotation and that isn't
available. Reversing the CW doesn't work because the bolt holes are
countersunk from one side and would not survive a double countersink.
As you can see in the wear picture, that isn't necessary, both sides
of the teeth being worn equally. Wearing forward and reverse faces of
each tooth would not lengthen their life so that has no benefit in my
perception.

Just replace the chain when it gets out of pitch. Chainwheels are the
least worry since they don't begin to skip when worn normally. It's
the driven sprockets that skip and the reason for that is obvious. A
new chain that is in perfect pitch cannot enter a sprocket if the
exiting roller is riding up into a wear pocket made by a longer
chain... so it skips over into a new engagement.

Jobst Brandt