so i built up my first fixie recently... originally i was running 46/15... put on the chain, cut off some links, got decent chain tension, beautifully quiet drivetrain

yesterday, i took off the wheel, lockring, replaced the 15t cog w/ a 18t cog, but the wheel back on, got what i figured is good chain tension, but now i get this ratchety sound coming from the cog when im pedaling.

ive read in different places that fixed gears should have a very quiet drivetrain & that a noisy chain could be a few things: bad chainline, binding chain or just the interaction of certain components & their quality. ive heard that its bad for chain wear & if your chainline is off bad enough, obv. thats a problem

ive also read of people w/ noisy drivetrains who say it 'just happens' w/ some parts or that its a matter of breaking in the cog/chain/etc.

so whats the consensus here?

im pretty sure my chainline is decently good. i remeasured it last night & the math works out. also, since i had good chainline w/ the 46/15, i dont see why that would change just by replacing my cog.

i dont know if its a binding chain either. i would spin my wheel and try to position my wheel in different parts of the dropouts & at different angles to see if maybe the cog was making contact w/ the sidewalls of the chain, but the sound never went away

at this point im thinking maybe it just has something to do w/ the chain. like the # of links i took out when i was running 46/15 was perfect for that combo, but now that i have an additional 3 teeth on my cog, the chain runs weird or something.

when i spin the cranks & watch the chain, it wobbles back & forth. is this normal? my roommate was saying that if my chainline was off, he would expect the chain to be skewing in one constant direction, as opposed to wobbling back & forth. he thought maybe the cog was not flush or something, which may cause the chain to wobble. this made sense to me somewhat

i dunno.

is this even worth worrying about?

1) this is most likely because you are running a brand new cog with a chain that has mated to the other cog, how long have you ridden this chain? also if you are running this chain too tight it will only make it noisier.
2) are you running 3/32 or 1/8 on the chain and cog?
3) i have no idea what you mean by wobbles back and forth, i would check to make sure your wheel is centered.

yeah, this is what i was guessing. couldnt be sure though.... the chain is brand new. less than a week old. i cut the chain to fit w/ the 15t cog. i didnt decide to switch out the 15t for the 18t until yesterday...

is this an issue? will the chain 'adjust' for the new cog or is it better to just get a new chain?

chainring, cog & chain are all 3/32

well, i dont have a repair stand, so i flip my bike upside down to work on it. when i spin the cranks & just watch the chain move through the course of the drivetrain, i can see it slightly wobbling left to right, right to left as it moves from the chainring to the cog. like i said, mathematically, i should have good chainline. im not entirely sure whats accounting for the wobble

ok, i would get a new chain (i usually do this whenever i change drivetrain components, but not always, chains are cheap enough that it's usually worth it). If you don't get a new chain, clean yours, lube it and make sure there are no binding links. Then when you put your wheel back on, make sure it's centered in the stays/track ends(or dropouts). and components take time to mate, so give it some time.

also, i have a feeling that this noise might be coming from your chain being too tight, because 3 teeth is a big jump to make without adding links. get a new chain and see how that works, 3/32 chains are cheap as dirt so it can't hurt.

cool, thanks for the advice, man