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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 08-17-10, 11:55 PM   #1
leslieliang
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Different Chain Tensions at Different Points

When I first got my Dawes SST AL and gave my chain absolutely no slack, I found that I would be able to pedal until my drive side is at about 12 - 2 o'clock. At this point, the chain tension was so tight, that I would not be able to pedal. Then, I loosened the chain tension a bit and the pedal can spin, but not freely. When I got to that same spot, I would get a lot of friction and the chain gets a lot tighter. I have no idea why this is happening.

At first I thought maybe it is my freewheel because it's a generic freewheel, but it occurs at the same spot everytime, so maybe not.

Then I thought maybe it's the chainring. Maybe the chainring is not a true circle and like an oval or something. Does anyone think I am correct?
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Old 08-17-10, 11:57 PM   #2
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Originally Posted by leslieliang View Post
When I first got my Dawes SST AL and gave my chain absolutely no slack, I found that I would be able to pedal until my drive side is at about 12 - 2 o'clock. At this point, the chain tension was so tight, that I would not be able to pedal. Then, I loosened the chain tension a bit and the pedal can spin, but not freely. When I got to that same spot, I would get a lot of friction and the chain gets a lot tighter. I have no idea why this is happening.

At first I thought maybe it is my freewheel because it's a generic freewheel, but it occurs at the same spot everytime, so maybe not.

Then I thought maybe it's the chainring. Maybe the chainring is not a true circle and like an oval or something. Does anyone think I am correct?
This, yes.

And you don't need to run super high tension on the chain. It creates unnecessary wear and tear on the drivetrain.

Last edited by rustybrown; 08-18-10 at 12:00 AM. Reason: heil seitan
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Old 08-18-10, 12:02 AM   #3
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You are correct, sir.

Sometimes chainrings are warped and your chain will have different tensions at different spots on your chainring. You could get a different chainring if the warped is really noticeable.
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Old 08-18-10, 12:06 AM   #4
leslieliang
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I get the perfect tension on the other spots of the pedal, but when I hit like 12-2o'clock, the tension is too much to spin freely. I think I am going to get a new chainring as I want to run 47/16. What are some companies that make good chainrings? (that won't break the bank, something like 20-50 dollars)?
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Old 08-18-10, 12:16 AM   #5
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Sometimes there's a bit of play in the bolts that hold the chainring allowing it to be held a bit off-center. With the cranks in the position where you get the most chain tension, try loosening all the chainring bolts just a little and then retighten them. See if that results in more even chain tension as you rotate the cranks.
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Old 08-18-10, 12:24 AM   #6
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Good point prathmann.

That was my case when I had a random tension problem, I still have different tension but it is so minimal that it's not really noticeable.
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Old 08-18-10, 12:30 AM   #7
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You are correct, sir.

Sometimes chainrings are warped and your chain will have different tensions at different spots on your chainring. You could get a different chainring if the warped is really noticeable.
Thanks for the suggestion. I just tried it, but it's still having tension problems.
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Old 08-18-10, 12:32 AM   #8
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http://www.sheldonbrown.com/fixed-co...html#chainline


http://www.bikeforums.net/archive/in...p/t-17337.html
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Old 08-18-10, 12:37 AM   #9
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Could also be the chain. I had an old chain that was stretched out in certain spots, so I got a new one and it immensely helped. (I had/have the exact same problem.)
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Old 08-18-10, 12:46 AM   #10
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A common issue with newbs is that they run their chains too tight... most drives with have some variance throughout the rotation as very few chain rings and cogs are perfectly round.

Back things off from the tightest point and then check it where it is loosest... you should be able to move the chain about half an inch at this point or see a little chain drop off the top.

Any more than this means you should try repositioning the chain ring or replacing it with a better one.
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Old 08-18-10, 09:31 AM   #11
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The chain rings are probably close to perfectly round when they are brand new. The thing is that the bolt holes are built with clearances so that there can be some tolerances for differently manufactured cranks. A laser precision super exact diameter bolt hole in your chain ring is no good if the person making the crank doesn't do the same thing. You would only be able to use it on specially made bikes. Also the bolts themselves are not always exactly the same diameter. So you need to have some slop in the size of your bolt holes. The result is that your chain ring can move around a bit when you tighten it down and won't be centred perfectly over the centre of your cranks.
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