# Uneven chain tension



## McrJ64 (20 Feb 2011)

When I turn my pedal, the chain tension changes. At one point it is much tighter than at other points. At one point it's particularly loose. Putting the wheel back in takes ages. I have to set the tension so that it's a compromise between the tightest and loosest points. Does anyone else have this problem and does anyone have a solution?


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## Alien8 (20 Feb 2011)

It's because the chainring isn't mounted centrally and probably also because it isn't perfectly round. Slacken the chainring bolts a touch so that the ring doesn't move when you rotate the crank but will if you give it a bit of a nudge. You can then work your way round moving the chainring a touch here and there until you're happy then tighten the bolts. Another method that I prefer is to remove the chain from the chainring then stick a bit of paper with a marker on it behind the ring on the chain stay. You can then see how the ring edge moves with respect to the marker and adjust it as above to get it central. That's what I do anyway.


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## Zoiders (20 Feb 2011)

Try a better quality ring.

A ring that actualy has a lump on one side - as in it's not round and the lump increases the circumfrence - that will cause a tight spot. It's a manufacturing fault that you can only fix with a replacement ring, if the circumfrence is wrong for the amount of teeth you can't change it by having a fiddle with the chain ring bolts.


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## McrJ64 (21 Feb 2011)

Thanks for the suggestions. It's not a 5 minute job to correct so I think it'll have to wait till I get a day off. Thanks again.


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## totallyfixed (21 Feb 2011)

It's the nature of chainrings, never had one that is perfectly round yet, I just remember what position my cranks are in at the tightest spot and always tension the chain in that position.


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## mickle (21 Feb 2011)

Your chainring might be perfectly circular but attached to a poorly machined chainset whose BCD was machined out of round.


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## dave r (21 Feb 2011)

Look about half way down this page http://www.sheldonbrown.com/fixed.html for centring the chainring on the spider. Your tight spots in the chain are probably a combination of a chainring, or cog, that isn't quite round and a chainring that's not totally centred on the spider. You might find that centring the chainring improves things but doesn't totally get rid of the tight spots. You might also find that after a few months the chainring wants centring again, they can move on the spider after they have been centred.


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## Riding in Circles (23 Feb 2011)

Your chain has stretched. It does not always happen uniformly, the odds are that the chain has stretched over a few links and now after adjustment the un-stretched portion has turned into a tight spot, you have to use a good quality chain on a fixed as you do not have a nice tensioner on the derailleur to look after the chain.


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## mickle (23 Feb 2011)

Catrike UK said:


> Your chain has stretched. It does not always happen uniformly, the odds are that the chain has stretched over a few links and now after adjustment the un-stretched portion has turned into a tight spot, you have to use a good quality chain on a fixed as you do not have a nice tensioner on the derailleur to look after the chain.



I've never heard of this and cannot imagine any circumstances which would allow this to occur. 

There's a simple way to find out. Spin the wheel and if the oscilation is in time with the cranks it has everything to do with the chainring/cranks/chainset. If it is in time with the rotation of the chain then Catrike's theory is correct.

I know what my money is on.


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## Zoiders (23 Feb 2011)

Catrike UK said:


> Your chain has stretched. It does not always happen uniformly, the odds are that the chain has stretched over a few links and now after adjustment the un-stretched portion has turned into a tight spot, you have to use a good quality chain on a fixed as you do not have a nice tensioner on the derailleur to look after the chain.


Not possible.

You would have to running a direct drive - perhaps a 20t sprocket on 20t ring to see a direct connection in wear like that.

Tight spots would cause more chain stretch perhaps but the tight spot would go away as the chain stretched, not the other way around as you suggest.


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## Gerry Attrick (23 Feb 2011)

Zoiders said:


> Not possible.
> 
> You would have to running a direct drive - perhaps a 20t sprocket on 20t ring to see a direct connection in wear like that.
> 
> Tight spots would cause more chain stretch perhaps but the tight spot would go away as the chain stretched, not the other way around as you suggest.


Catrike is perfectly correct.

When I was involved with vintage motorcycles, it was common to find chains which were worn unevenly. In fact I'd go so far as to suggest that that is the most likely cause of the problem, assuming the rear chainset and sprockets are of good quality. The relative sizes of the sprockets was irrelevant, but the quality of the chain did make a difference. I understand that modern o-ring sealed motorcycle chains suffer less from this problem than the old unsealed type which was and is still used on some motorcycles today. Cycle chains are most certainly not exempt from this type of wear.


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## Zoiders (23 Feb 2011)

Gerry Attrick said:


> Catrike is perfectly correct.
> 
> When I was involved with vintage motorcycles, it was common to find chains which were worn unevenly. In fact I'd go so far as to suggest that that is the most likely cause of the problem, assuming the rear chainset and sprockets are of good quality. The relative sizes of the sprockets was irrelevant, but the quality of the chain did make a difference. I understand that modern o-ring sealed motorcycle chains suffer less from this problem than the old unsealed type which was and is still used on some motorcycles today. Cycle chains are most certainly not exempt from this type of wear.


Thats not what I said.

I said that uneven chain stretch is caused by tight spots and the tight spots go away as the chain wears and will remain gone until you have to retension the chain, they will vanish pretty much all together as the ring wears with the chain and the sprocket/ring ratio - not the other way around.

Think about it, what catrike suggests has no logic to it.


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## Gerry Attrick (23 Feb 2011)

No.

In my extensive experience, tight spots do not "go away". In fact they become more obtrusive as the chain wears. This will eventually result in total failure.

On what basis do you make your assertion?


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## Zoiders (23 Feb 2011)

Gerry Attrick said:


> No.
> 
> In my extensive experience, tight spots do not "go away". In fact they become more obtrusive as the chain wears. This will eventually result in total failure.
> 
> On what basis do you make your assertion?


You are suggesting one-to-one wear ratios, that's not the case is it?.


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## Gerry Attrick (23 Feb 2011)

Zoiders said:


> You are suggesting one-to-one wear ratios, that's not the case is it?.



Lost me there Zoiders.


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## Zoiders (23 Feb 2011)

Gerry Attrick said:


> Lost me there Zoiders.


Chain wear does not occur on a one to one basis, you aren't getting the tight spot at the same point on every revolution and you arent getting it in one place on each chain.

Rings cause tight spots, not uneven chain quality.

See also Sheldons article about skid stops.


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## Gerry Attrick (23 Feb 2011)

Exactly. The tight spot positions will appear to change due to different sprocket size. If the tight spot did appear say every time the left crank was horizontal forward, then yes the ring may be suspect, but when the position of the tight spot appears to change in relation to the crank position, the tight spot is chain related.


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## McrJ64 (24 Feb 2011)

The bike has a 42 tooth chainwheel, 16 tooth sprocket, 100+ tooth chain. I think we can agree that the chain will be 'shifting' on the chainwheel and sprocket, i.e any given link in the chain will not consistently meet the same tooth on the chainwheel and/or sprocket. The chain is however tight at the same spot on every revolution of the chainwheel.

I tend to agree that the problem is therefore with either the sprocket or the chainwheel.

The bike has always been like this, even though I have changed the sprocket a couple of times, and regularly change between freewheel (commuting) and fixed (weekend), so I and tending to doubt that chain wear is significant (it may well be contributing).

Thanks for all the thoughts. They are really interesting.


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## McrJ64 (28 Feb 2011)

Apologies to Catrike. Last week he said that the uneven tension was due to chain wear and I doubted him. Well, I changed the chain on Saturday and the tension was much more even. I still don't understand why but I like it. I think I'll have to change it more frequently in future.


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## Riding in Circles (28 Feb 2011)

McrJ64 said:


> Apologies to Catrike. Last week he said that the uneven tension was due to chain wear and I doubted him. Well, I changed the chain on Saturday and the tension was much more even. I still don't understand why but I like it. I think I'll have to change it more frequently in future.




No worries, I am in the trade and have 30 years of experience, so I know fine well that everyone knows better than me until they do what I suggest, glad you have it sorted.


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## Zoiders (28 Feb 2011)

Catrikes still wrong.

Abritrary answers based on "because I said so" usualy are.


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## Riding in Circles (28 Feb 2011)

Where is the zombie smilie?


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## Zoiders (28 Feb 2011)

You have given an answer with no explanation other than "I'm in the trade so I must be right".

It's tosh.


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## Riding in Circles (28 Feb 2011)

Zoiders said:


> You have given an answer with no explanation other than "I'm in the trade so I must be right".
> 
> It's tosh.



You seem to have missed the fact that my answer fixed the issue, go and sit in the corner and argue with yourself, there's a good boy.

I am just happy to have helped the chap, you seem upset that he was helped by someone other than you, perhaps a case for self examination on your part.

My criteria for my hypothesis is not based on being in the trade but rather my experience with pedal cycles and nine times out of ten the issue described has been caused by the chain having stretched in all but a few links, sorry if that is not good enough for you but it is what it is and it is correct.


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## Zoiders (28 Feb 2011)

Now you are changing your story.

Before you were adamant that it was a chain with a few worn links, suddenly you are saying it's chain that has reached the end of it's life.

On a good condition chain tight spots are caused by ring and spider issues, not the mythical patchy chain wear, everyone else said you were wrong not just me, and you remain wrong.

If you don't know the answer don't make stuff up, 30 years "in the trade" or not.


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## Riding in Circles (28 Feb 2011)

Ok, I'm wrong, the chap should return his bike to the condition it was and try all your expensive solutions quite clearly, the people who agreed with me are idiots and the damaged chain is obviously damned to hell for disagreeing with you as well. 

Your a funny little sausage, I'll give you that.


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## Zoiders (28 Feb 2011)

x-hundred miles from now there will be the same wear pattern and the same problems because the chain ring is out of true.

It's a common fault and it's a cheap fix compared to endless chain replacement.

"Funny little sausage"?

Go and patronize another member.


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## mickle (28 Feb 2011)

The only thing that I can think of which could cause uneven chain wear is uneven application of lube. Unless Catrike has any other ideas. Do people really lube one part of a chain and not the other?


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## Riding in Circles (28 Feb 2011)

mickle said:


> The only thing that I can think of which could cause uneven chain wear is uneven application of lube. Unless Catrike has any other ideas. Do people really lube one part of a chain and not the other?



I have seen the issue on motorcycles as well, especially ones that people wheelie, so I suspect it is some sort of issue with shock on the chain and lets face it, bicycle chain is quite light weight considering its application, there is certainly more stress on a chain on a fixie than any other bicycle, of course the ideal is to change chain and sprockets together but sometimes it is possible to just have a wrecked chain.


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## mickle (28 Feb 2011)

Catrike UK said:


> I have seen the issue on motorcycles as well, especially ones that people wheelie, so I suspect it is some sort of issue with shock on the chain and lets face it, bicycle chain is quite light weight considering its application, there is certainly more stress on a chain on a fixie than any other bicycle, of course the ideal is to change chain and sprockets together but sometimes it is possible to just have a wrecked chain.



I disagree entirely that there is more strain on a fixie than any other bicycle. My fixed chains always last longer than those on my geared bikes by virtue of not having to deflect across a block. 

On an upright bike the load on the chain is affected by the relative diameters of the sprockets and chain-rings and by the weight of the rider. As you'll no doubt be aware the load on the chain of a recumbent isn't limited by the rider's weight since a rider can exert a force on the pedals in excess of his body weight by pushing back against the seat.. 

You still haven't explained the mechanism by which bicycle chains wear unevenly.


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## Gerry Attrick (28 Feb 2011)

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.


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## mickle (28 Feb 2011)

Gerry Attrick said:


> 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.
> 
> ...




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

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


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## Gerry Attrick (28 Feb 2011)

mickle said:


> 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.


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## Riding in Circles (1 Mar 2011)

Gerry Attrick said:


> 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.


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## mickle (1 Mar 2011)

Catrike UK said:


> 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?


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## Riding in Circles (1 Mar 2011)

mickle said:


> '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.


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## dan_bo (1 Mar 2011)

Has the chainring got 'boipace' written on it?

oh, he's fixed it.


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## mickle (1 Mar 2011)

Catrike UK said:


> 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.


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## Riding in Circles (1 Mar 2011)

mickle said:


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



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.


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## mickle (1 Mar 2011)

No-one expects the Spanish Inquisition!


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## mickle (1 Mar 2011)

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.


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## Dayvo (1 Mar 2011)

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


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## RecordAceFromNew (1 Mar 2011)

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.


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## Riding in Circles (1 Mar 2011)

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.


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## steve52 (1 Mar 2011)

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.


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## steve52 (1 Mar 2011)

oh i typed these thoughts without reading the post above, we seem to have a conscensus,


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## Gerry Attrick (1 Mar 2011)

Catrike UK said:


> 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.
> 
> ...




You have far more patience than I!


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## Riding in Circles (1 Mar 2011)

Gerry Attrick said:


> You have far more patience than I!



I had some time while I was setting some stuff up so I thought I would explain how bicycles function.


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## mickle (1 Mar 2011)

Catrike UK said:


> I had some time while I was setting some stuff up so I thought I would explain how bicycles function.




Making shoot up doesn't qualify as facts. Just so you're aware.


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## Riding in Circles (1 Mar 2011)

mickle said:


> Making shoot up doesn't qualify as facts. Just so you're aware.




So what you are saying is that despite asking for some sort of explanation you are not really interested anyway as you have got your special la la blinkers on, ok, I'll ensure I will not provide any advise if you suffer problems, everyone else is fine though, I am sure that will upset you as you keep throwing all your toys out of your pram on every other post.

You can have the last word now as I am washing my hands of you, bye bye.


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## Zoiders (1 Mar 2011)

Firstly - stop comparing motorbike chains with bike chains.

Yes they are both roller chains and both experience roller wear, a motorbike chain however is getting such an amount of tourque through it that doing things like pulling a wheely which gives a short sharp tug on the chain against the weight of the rider and bike can actualy stretch and elongate the pin hole so you really are stretching the metal and making the link longer, especialy if you keep gunning the throttle to keep the wheel in the air and keep yanking at that chain.

You aren't going to do this with a correctly linked bike chain, even with variations in the heat treatment process you aren't exceding the pull strength of the side plates, what is possible is for roller wear to become excelerated by a badly machined ring.

I don't have to defend myself against people who make shoot up - as Mickle said.


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## Gerry Attrick (1 Mar 2011)

Zoiders said:


> Firstly - stop comparing motorbike chains with bike chains.
> 
> Yes they are both roller chains and both experience roller wear, a motorbike chain however is getting such an amount of tourque through it that doing things like pulling a wheely which gives a short sharp tug on the chain against the weight of the rider and bike can actualy stretch and elongate the pin hole so you really are stretching the metal and making the link longer, especialy if you keep gunning the throttle to keep the wheel in the air and keep yanking at that chain.
> 
> ...



For the third time of asking, your qualifications for asserting this are what, exactly?


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## Zoiders (1 Mar 2011)

Gerry Attrick said:


> For the third time of asking, your qualifications for asserting this are what, exactly?


Youre just pissed of that mickle and I can look at the problem, have a quick think and then explain the problem correctly in laymans terms when the lengthy preachy answers the other guys and you gave are a load of arbitrary nonsense.


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## Gerry Attrick (1 Mar 2011)

Thank you Zoiders. I have no need of further comment.


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## mickle (1 Mar 2011)

What Zoiders said.


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## Norm (1 Mar 2011)

Catrike UK said:


> 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.


I don't get this bit. Because the fluctuations are not synchronised (pah, how can you have UK in your name and use the z version  ) does that not mean that the wear occurs at a different part of the chain with each revolution, which means that the chain would wear evenly?


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