Singlespeed & Fixed Gear - Odd Chainring Question

PLEASE forgive me if some kind of search might help me here, none of the terms I tried turned up anything.

Basically my chain will go slack and then tight with each revolution of the chainring, not so much that I notice when riding other than the sound changing, but still enough that it can go from almost totally tight to about 1/2 inch of slack (based on my perception, not actual measurement). I tried loosening all the chainring bolts and shifting the chainring around, but that didn't help.

I guess I'm trying to see if anyone else has experienced this and/or might have some sort of advice about it. Thanks!

That's a lot of slack, what kind of chainring is it? Turn the bike on its side and pedal the crank, if the chain doesn't fall off it should be ok but I'd just go buy another chainring.

Does your chainring say "biopace" on it?

But seriously, a lot of "round" chainrings are not exactly so. I wouldn't worry about it.

When you tighten your back wheel, pay attention to how the cranks are positioned. If you like your chain tension piano-wire tight, position your cranks where they would be on the slack side. If you like a little slack (as I do) then position them where they would be when the chain tightens up.

Its a Rocket that came on my IRO. Yeah it doesn't fall off. Seems like a pretty structurally substantial ring, there's not any way I warped it somehow?

I just got a rocket, and it is surprisingly ovalized for such a large chunk of aluminium. and yeah, i noticed it before i rode on it, so it isn't anything you did to it while riding. i think it's just the manufacturing.

this can be alleviated by recentering the chainring on the crank spider. sheldon has instructions here (http://sheldonbrown.com/fixed.html) under the "Chain Tension" section.

i had the same problem with my iro crankset, and I could never get it to the point where the chain tension didn't vary considerably. i ended up replacing it with a sugino 75 crankset & ring and I couldn't be happier.

I suppose I may be being too sensitive about it, it all still works I guess.

Cool, thanks for the link, might help.

I don't think you are being too sensitive, it [I]is[I] annoying. It shouldn't cause any major problems, as long as it isn't super tight at its tightest point.

All this means is that your chainring is not perfectly round. I've heard about these problems with alot of low-mid range rings. My TA Spec was a little oblate right out of the box, it pissed me off. The only real option you have is to upgrade the ring. But this is not really necessery if it doesn't both you that much. Just make sure that when you check your chain tension as part of scheduled maintainence that you check it all the way around the ring.

Yep I'm definitely still learning about all this stuff. I think I improved the situation and in any case it seems like something that is live-withable unless I want to buy a more pricey chainring (which at the moment I cannot)

Thanks for the input.

I had the same problem with my Rocket Ring.

well, my rocket ring seems to be doing the same, perhaps I'm not insane.