Uneven chain tension

[McrJ64]

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?

 

[Alien8]

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.

 

[Zoiders]

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.

 

[McrJ64]

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.

 

[totallyfixed]

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.

 

[mickle]

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

 

[Deleted member 1258]

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.

 

[Riding in Circles]

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.

 

[mickle]

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.

 

[Zoiders]

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.

 

[Gerry Attrick]

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.

 

[Zoiders]

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.

 

[Gerry Attrick]

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?

 

[Zoiders]

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?.

 

[Gerry Attrick]

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

Lost me there Zoiders.