Help with chain tension
 

I'm putting my new bike together and i'm trying to even out the chain tension. I know what i'm supposed to do with loosening ring bolts and then micro adjusting the tension, but it doesnt work. I checked and the chainring seems to be free of wobble, the cog has zero wobble, but there is still a big difference in tension between two opposite crank positions. I tried rotating the chainring position around to see if that was causing, but each time the tight/slack occurs at the same points. So what else? Chain tension is just about the worst thing about the fixed gear :notamused:

I just get the chain just under tight on the "loose spot" of the ring so it's tight on "tight spot" but not extremely

Chainrings aren't perfectly circular. It's just something you have to deal with. You just need to make sure that the chain doesn't bind at the tight spot or else you'll wear your drivetrain out quicker.

I understand that but the problem is that the difference is just too big. My previous bike had uneven chain tension too, but not this much. I'm just wondering what else can i check?

Do you notice it while you ride?

If you've already tried the chainring trick there is nothing else to do besides new components and a new frame. Some combinations will be worse than others. Live with it or start spending money which may or may not "fix" it. If you're not dropping the chain on bumps with correctly tensioned chain then there isn't a functional problem.

This is not correct.

The drivetrain should not result in a laser tight, binding drivetrain at any point of the rotation.

this is probably a dumb question, but it happened to me once... are you sure that your chainring is not biopace?

it was a dumb question... didn't read the op closely, e.g. "new" bike, etc...

If the tight spot follows crank position even with rotating the ring one bolt position, that would suggest something like a bent crank spindle or ecentricity somehow with the BB.

Yep tried rotating the chaining around and the loose/tight positions are the same. The frame and bb are brand new, and the bb was installed by the shop a few days ago.

Or it might suggest something with the spider. I guess ill live with it for a while but i'd always worried about dropping the chain.

Can you force the chain off at the loosest point (push the chain to the side while turning the cranks, as though you were derailing the chain)? If not, or if it's pretty difficult, then I wouldn't worry too much about it. Also, make sure you don't have any stiff links in your chain. Chances are, the issue is probably not something worth paying attention to.

Yeah maybe you're right. Its just that i know the chain tension should be more even, like it was with my previous bike. Oh well. Ive never had a chain come off, what exactly happens when it does?

http://files.turbosquid.com/Preview/...3.jpgLarge.jpg..

Well i measured the chain travel and the loose spot moves ~10-12mm more than the tight spot (total travel up+down). Not sure if this is a lot, but sure looks a lot.

If it doesn't derail easily, it's fine. 10-12 mm sounds about right.

the "extremely" tight part is what I meant for laser tight, binding.

There is an easier way to determine if a paritcuarly drivetrain will drop a chain. Manually try to derail the chain to the inside while pedalling the bike on the stand. If the chain does not come off while doing this test, then it won't come off on the road.

i like at the tightest point to have at least 5mm of travel. 10 is fine imo. i like max under 20mm or so

if it's still bothering you, have you tried rotating your chainring (like unbolting it from the arm, then rebolting it one hole over). maybe the arm and the ring are each a little out of round, but they're lined up and working against each other.

i wouldn't worry about it though.

Yes i tried all five position and still the same thing at the same place. So i dont know what the problem is, its just annoying visually seeing the chain go tight and then go slack :twitchy: