Uneven chain tension

[Gerry Attrick]

I sometimes wonder why I bother answering technical queries. Like I said earlier, Catrike is absolutely correct. He has thirty years of experience, I have forty years in. I have been involved with cycles, motorcycles and industrial (marine engine) chain drives all this time. Where an exposed chain is operating under load, this uneven wear pattern is manifested. Period. You amateurs can pontificate all you like about eccentric chainrings, but modern chainsets are manufactured to very tight tolerances and it is highly unlikely to be the cause of the symptoms described by the OP.

Changing the chain has solved the OP's problem, and yes the problem may or may not recur in the future, but replacing brake blocks is only a "temporary" repair for ineffective brakes.

"There is none so deaf as those who won't hear" is a true adage. Those who are clearly stone deaf see fit to tell the orchestra it is out of tune!

In my previous post I asked Zoiders for the basis of his assertion. He failed to respond to that question. Catrike and I have proffered our credentials. Now is his oportunity.

 

[mickle]

I sometimes wonder why I bother answering technical queries. Like I said earlier, Catrike is absolutely correct. He has thirty years of experience, I have forty years in. I have been involved with cycles, motorcycles and industrial (marine engine) chain drives all this time. Where an exposed chain is operating under load, this uneven wear pattern is manifested. Period. You amateurs can pontificate all you like about eccentric chainrings, but modern chainsets are manufactured to very tight tolerances and it is highly unlikely to be the cause of the symptoms described by the OP.

Changing the chain has solved the OP's problem, and yes the problem may or may not recur in the future, but replacing brake blocks is only a "temporary" repair for ineffective brakes.

"There is none so deaf as those who won't hear" is a true adage. Those who are clearly stone deaf see fit to tell the orchestra it is out of tune!

In my previous post I asked Zoiders for the basis of his assertion. He failed to respond to that question. Catrike and I have proffered our credentials. Now is his oportunity.

Neither of you 'experts' has yet explained how uneven chain wear occurs.

Correction: Many modern chain-rings are not manufactured to tight tolerances.

 

[Gerry Attrick]

Neither of you 'experts' has yet explained how uneven chain wear occurs.

Correction: Many modern chain-rings are not manufactured to tight tolerances.

I am an engineer, not a physicist. I make my assertion from forty years of observation and getting my hands dirty. If you buy cheap, inaccurately machined chainsets, then you get what you paid for.

 

[Riding in Circles]

I am an engineer, not a physicist. I make my assertion from forty years of observation and getting my hands dirty. If you buy cheap, inaccurately machined chainsets, then you get what you paid for.

Indeed, you offer a bit of advice free of charge from your experience which turns out to be correct, then the "no good deed goes unpunished" brigade kick into overdrive, sad.

 

[mickle]

Indeed, you offer a bit of advice free of charge from your experience which turns out to be correct, then the "no good deed goes unpunished" brigade kick into overdrive, sad.

'Turns out to be correct'?

I ask again: What is the mechanism which causes this alleged uneven chainwear?

 

[Riding in Circles]

'Turns out to be correct'?

I ask again: What is the mechanism which causes this alleged uneven chainwear?

As in the OP has posted that the chain replacement has cured his issue?

Answer to your second query is "use".

Thank you and good night.

 

[dan_bo]

Has the chainring got 'boipace' written on it?

oh, he's fixed it.

 

[mickle]

As in the OP has posted that the chain replacement has cured his issue?

Answer to your second query is "use".

Thank you and good night.

Well it's rather oversimplifying it to say that it's 'use' which causes wear but lets not get picky.



I'll ask you again: What causes the alleged uneven wear?

If you don't know just say.



And you might convert more folk to your way of thinking if you moderated your tone.

 

[Riding in Circles]

Well it's rather oversimplifying it to say that it's 'use' which causes wear but lets not get picky.



I'll ask you again: What causes the alleged uneven wear?

If you don't know just say.



And you might convert more folk to your way of thinking if you moderated your tone.

I have already answered this question, it is based on real life experience, I have no wish to convert anyone, I simply offered advice based on said experience, I never expected the spanish inquisition.

 

[mickle]

No-one expects the Spanish Inquisition!

 

[mickle]

You haven't answered this question: What is the specific process which leads to uneven chain wear? If you don't know just say.

Zoiders and I are not idiots. We too have very many years of experience. You don't have a monopoly on that. Except that neither of us have experienced the phenomenon of uneven chain wear.

Nor can we imagine how such a thing occurs.

Now it may be that we haven't witnessed it because we weren't looking for it - after all if one part of a chain is worn, why measure a different section of it?

But the fact remains - he and I remain unconvinced because we cannot conceive of a set of circumstances which would lead to uneven chain wear occuring. It doesn't make sense.

So we remain unconvinced. Sorry if that gets up your goat.

Unless of course you have any theories.

 

[Dayvo]

I've enjoyed watching this little jousting session (too many toys being thrown, though).

Why not google and investigate for yourselves?

http://www.google.co.uk/search?sour...z=1T4ADBR_en-GBSE217SE218&q=uneven+chain+wear

 

[RecordAceFromNew]

Fwiw guys I think you are all correct.

Perhaps just a little physics will help put the issue in perspective.

Convention wisdom has it that one should set the chain tension of a ss/fixie so that the chain can flex around 1cm up and down mid way between the chainset and rear sprocket. Typically that is around 20cm from either axle (because most chainstays are roughly 40cm long). This ~1cm figure may or may not be consistently achievable depending on various things, but can be seen as a target in compromising between too tight (which wears the drivetrain out and zap energy unnecessarily) and too loose (which increase the likelihood of accidental chain derailment).

Geometry tells us that 1cm of vertical flex on such a 20cm horizontal requires an extension of 0.25mm [because it is ~20 x (1 - cosine (arctangent(1/20)))]. Conversely, what that means is with that drivetrain if chain tension is set at a point where the flex is maximum a mere half a mm out in chain length and/or out-of-roundness will give rise to extreme tightness and binding, likely less to make it capable of being felt.

To put 0.5mm in perspective, the recommended limit for chain stretch allowed before replacement is 1/16" for one foot or 12 complete links of chain, which is 2.1mm for 40cm of chain. Of course the 0.5mm uneveness can also be contributed by out of roundness of the sprocket, or spider arm, or chain ring, or axles etc.

The point though is that 0.5mm is very small, indicating only the tiniest imperfection is needed to cause similar drivetrains to have tight spots under tension, which explains why practically all good guides on this and related machines suggest chain tension to be set loose enough at the tight spot of a drivechain. Guides on EBB such as this and this come to mind. Park e.g. suggests targetting 6mm flex at the tightest spot. In other words, although they may differ by degree, tight spots practically invariably exist, and good mechanics know how to fix big ones and work around small ones properly.

In the case of the OP's bike, it is quite likely that it was never set up properly, because I think he said it had always behaved like that. Since the pins and plates of a chain are tiny and weak in relation to sprocket, chainset and their axles, it would have been inevitable that the chain got ruined through use. Hopefully when the new chain was installed, as Catrike and Gerry recommended, it was set up properly.

 

[Riding in Circles]

There are several reasons that chains and sprockets can wear unevenly. First of all, you might think that the delivery of energy from the pedals to rear wheel is a smooth flow, but cadence plays a part. The the through stroke of the crank is different for each leg, cadence alters depending on load, hills etc... and while those changes in cadence usually are impossible for the rider to perceive, they impose ever-varying taut-slack loads on the chain.

To a lesser degree, the same thing happens in reverse on using the pedals to slow down.


Next time you ride alongside another bicycle, watch the chain and you'll see that even when moving at a steady speed and seemingly smooth cadence, at least some part of the chain is usually fluttering up-and-down. As pedal revolutions increase in speed this fluttering is often more pronounced as the cadence becomes raggy.

These fluctuations change according to cadence, load and riding style, and they are not synchronized to the ratio of the sprockets. Consequently, the cumulative wear they impose on the chain and sprocket almost can't help being uneven.

Other factors compound this basic wear pattern. Water and dirt usually do not accumulate in equal amounts all around the chain and sprockets; a little more corrosive material in one place or another will cause uneven wear. Plus, after a ride when the chain is warm, some part of it cools on the straight runs between sprockets while the rest of it does so while wrapped around the sprockets. Depending upon the nature of any contamination that has accumulated on the chain, as well as the lubrication on or in it, that difference can easily cause a slight kink that usually goes away during the next ride but, in the process, still causes a little extra wear in those kinked areas. And once a wear pattern starts in one place on the chain or sprockets, the rate of wear tends to accelerate more there than on the rest of the chain.

 

[steve52]

mm i have to have a pennys worth, uneven chainwear dose happen,though i have not seen it to the extentent talked about what causes it, ive never though about it,could it be rust? getting more of a hold on some links and bearing sufaces? to me in theory i think it should not happen as the load should be delivered evenly but on a cycle there is deff tow power phases to a peddle turn, could this pulsing acount for uneven wear? anyway thats my thoughts on the why i now file it under od crap happens.