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Chain tension keeps alternating between loose and taut on ss setup.

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Chain tension keeps alternating between loose and taut on ss setup.

Old 06-13-19, 07:51 PM
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krecik
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Chain tension keeps alternating between loose and taut on ss setup.

Here's another small issue that's been bothering me lately.

I'm riding a ss setup with a coaster hub and I can't get the chain tension to stay put.

I've adjusted it several times now to the tension I want and what happens is it won't stay the way I adjusted it.

After a long climb it becomes too tight and after a long descent it becomes too loose.

And I don't get why? I'm tightening the wheel bolts as tight as I can, the wheel shouldn't be moving or allowing for any play.

Is this normal?

Kret
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Old 06-13-19, 09:14 PM
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Cogs and rings (and the spiders the rings attach to) are rarely really close to round. Of course the more expensive stuff is closer, usually at least. The peaks and lows of the sprockets generally follow a rotational pattern. But the rear and front rotate at differing rates so the matching of the two sprockets varying highs and lows come at odd intervals (unless the ring is an even multiple of the rear cog).

I don't know why after an extended climb or decent the range of tension changes, unless it remains the same and the observation is what's off.

BTW the proper chain tension for non spring loaded systems (like a single speed or track set up) is NO TENSION. Andy
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Old 06-13-19, 09:24 PM
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Try centering the chainring.

https://sheldonbrown.com/no-derailers.html#centering


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Old 06-13-19, 09:37 PM
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After you install the rear wheel, do you rotate the crank and see if the chain gets too loose or too tight as you do ? I'll bet it does. As Andy said, drivetrain parts are rarely actually round with the holes for the chainring bolts exactly on a circle around the BB axle. The tapers that slide over the BB spindle may also be not quite on center. The BB spindle also. Fact is, careful machining to get all that "right" takes skill and accurate machines and that costs money. Manufacturers of road bike parts often cut corners here because on derailleur bikes, being round matters little. There has even been speculation over the years that a little out of round (or wobble) tends to speed up shifts in front a little.

Now if you seek out parts intended for track racing,you will find (in general) a real step up in roundness because now it matters. I'm guessing the weakest point of your system (chain "tension"-wise) is your crankset. (Pure guess since you have not told us what you are riding.) There are tricks to improve a mediocre crankset. Sheldon Brown spells out one approach. You also might try rotating the chainring say 2 bolt holes (on a 5-bolt crankset) and see if that helps.

Sheldon's chainring centering. Scroll down to almost the bottom.

https://www.sheldonbrown.com/no-derailers.html

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