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Bend, OR
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Discussion Starter #1
Okay, I know this has been asked about before, but what causes the eneven chain tension at different points in the pedalstroke? Chainring placement? How do you get rid of this? I have tried moving the chainring to avoid this but I always end up with the tension perfect when one pedal is forward and too tight when the other is forward. This happens on two of my singlespeeds.

Obviously, I could just make it loose enough so that it doesn't bother too much, which is what I have done with one of the bikes, but this isn't really an option on the other one.

Any suggestions?
 

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i would guess that your chainrings are not perfectly round or symmetrical, which i believe is somewhat common. that would give you different tensions thru out the pedal stroke.

i have seen this on my ss's with chainrings made by raceface, eno and boone.
 

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Basically once the chainring is mounted to the crankarm, there is a slight difference in the 2 centerpoints. Even the slightest difference will cause this. You don't want you chain to be super tight, but instead with just a hair of play (just enough to not cause the chain to get tight when pedaling). This will make you're bike pedal more efficiently.

Do this. Make your chain super tight and spin your cranks backwards and see how much they spin. Now do it again but with a little less chain tension.
 

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I found the chainring on my SS could be installed on the crank arm spider so that it wasn't centred perfectly. This lead to uneven chain tension, unless it was REALLY carefully installed. I've had better luck with Salsa chainrings - the inside part of the chainring seems to butt up against the crank arm spider, so it's pretty much impossible to install off centre.

The worst solution is to slacken off the chain tension. It seems like a good idea until you drop a chain and go straight over the bars :eek:
 

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It's everything, Hub, freewheel, Bottom bracket, crank, chain ring. all of these things have tolerances on how round they are. if any one thing is not perfectly round it will cause this. More often then not, multiple things are not perfect and they can either lessen or intensify the effects. In 10 years working in shops I have yet to build a SS mtb, bmx bike or beach cruiser that didn't have this issue.

Loosen the chain enough so there is no binding and go ride.

Even on geared bikes you'll see the cassette move a bit as it is freewheeling do to imperfections in manufacturing.
 

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bike dork
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You can eliminate some of the uneven tension by "walking" the chain. Sheldon Brown gives a nice description of how to do this. Basically you loosen all the CR bolts to ~ finger tight. Next spin the cranks and find the tight spot, or spots. Whack the chain with a screwdriver handle, etc. Keep spinning the crank, finding the tight spot(s) and striking the chain. Repeat until the tension is more even. Now tighten the bolts like you would lugnuts and test it out. The idea is that by striking the chain you move the chainring a little bit to help remove the tension. It definitely works, it may take a while but the more you do it the easier it gets.
 

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Try indexing the chain ring around the crank. You may get lucky and find a spot where the bad tolerances get close to canceling each other out.
 
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