Singlespeed & Fixed Gear - Light tension; Heavy tension.

I am having a problem with the chain tension on my SS. I have a 17" steel Specialized Stumpjummper. I am running a 32t ring and a 18t cog. I am able to do this without a tensioner. The problem is the tension is greater at certain points in the cranks revolution. It looks like the chain is actually going up also. Is the chainring squashed? I cant tell by looking at it. Any ideas would be great. It isn't really causing a problem besides probably wearing the ring out faster.

Also I am using an older 9 speed chain(about 300 miles). I held the chain up tp another 9 speed with more miles(road) and the one I have on the singlespeed is about a 1/4'" longer at the same link. Can a chain stretch that much? I tried the chain off the road bike and it was so tight the wheel wouldn't go all the way into its groove. I was hoping to be able to go without a tensioner. Would it be a better idea to just put a tensioner on and buy a new chain and add 2 links?

sounds like your chainring is worn, or just poorly made to begin with. no chainring is perfectly round, but some are better than others. salsa rings arent too much money and are pretty round. if you can, avoid tensioners.

if you replace your chainring, you might as well get a new chain and freewheel to avoid compatibility problems due to worn parts.

Its very normal to have tightspots, but if you are using one of the original ramped rings from your crankset, they are very poorly made (the stamped steel ones anyways). Mine on my ghetto beater SS is ovalized to the point where I had to file the crank to fit it. If you order a good Surly steel CNC'd ring it will be about as perfect as possible and very resistant to bending/warping.

For the chain, you can add a KMC Half Link to the chain which is just as it sounds, a half a chainlink to replace a full link, so you can get that new chain to fit. It might make it too long as the chain wears, however. I usually use a PC1 BMX chain since they stretch very minimally in my experience.

did you bolt the chainring on tightening one bolt at a time? that usually sets up the chainring off center. you should tighten each bolt a little at a time in a star pattern until they are all tight.

also, if you are using a thead-on freewheel, most have tight/loose spots in them. from all the white industries eno freewheels i have seen or heard of, none have this problem. cassettes usually do not have this problem either.

check out http://www.sheldonbrown.com/fixed.html#tension
he describes a method for centering your chainring. i've yet to actually try it but i need to cause i'm having the same issue on a bike.
still sounds like you need a new chain though.

Thanks everyone. I figured it was a poorly made ring. It is a middle ring off a Race Face Prodigy crank. It is a stamped ring.

I have never heard of a half link I will look into that thanks.

I was planning on getting a new ring as soon as possible. I will get a chain at the same time. The cog is a DX cog with less than 50 miles so I figure it will be fine.

sweet. im always glad to hear of new SS MTB converts. this forum is mostly fixxers, not enough SS MTBrs. fixed gears are the best training tool for SS MTBing though, IMO.

I think I will post some pics.

Oh yeah, bought a Salsa ring and a new chain today.

There is a clearance around the spider where it butts against the chain ring too. This accounts for a lot of the variation. I actually used shim stock and shimmed my chain ring to the exact middle. This does not help any off center in the rear wheel, but I am able to run my chain a little tighter without having to have an extremely loose spot. I think that helps keep the chain on at high rpm or stress. There will always be a little variation due to manufacturing tolerances of all the parts.