Singlespeed & Fixed Gear - Fixed Gear Chain Tension

Hello:

I've put together a fixed gear bike and am having a bit of trouble with chain tension.

The chain is much tighter at one point of the crank revolution than the rest.

I tried rotating the chainring on the spider, thinking that the ring was out-of round (this is a heavily worn chainring). Unfortunately this had no discernable effect.

My next thought is that the spider arms are out of round, but i am not quite sure what the best method of checking that would be.

Anyone have any ideas for me?

Thanks,
Matt

PS. No, the chainring is not a BIOPACE.

I was going to ask if it was a Biopace (there are other similar rings, too), but there are other things it could be.
Have you checked the chain for a tight link? Fixed gear bikes are very sensitive to tight links, and when I attached my half link, it took me a half-dozen adjustments to the pins to get the links riding smoothly (actually used a small screwdriver to loosen a link up a bit.
Here's something else to check: Is your BB spindle bent? Does the cog run true? Are you sure the chainring is true? Maybe the ring is too worn out-do you have another ring to try?

Alex:

I am pretty sure that my new track cog is good and round.

I checked the chain for stretch and it appears to be a nearly new chain. This could be part of the problem as the chainring is so worn that the new chain does not seat properly between the teeth.

I believe that my bottom bracket spindle is fine. The cranks spin nice and balanced.

I think I should get a new chainring to match with the newer chain.

I was hoping not to have to spend $30 more dollars on a bike that was supposed to be a very cheap project. But I must say, I really enjoyed riding her this weekend. It is so simple and elemental... and fast. I feel as though the bike is pushing me to go faster.

Anyone have a good cheap source for a 41 or 42T 144BCD chainring?

Thanks,

Matt

world class cycles (http://www.worldclasscycles.com)

Originally posted by SpotmaticF
I tried rotating the chainring on the spider, thinking that the ring was out-of round (this is a heavily worn chainring). Unfortunately this had no discernable effect.

My next thought is that the spider arms are out of round, but i am not quite sure what the best method of checking that would be.

Anyone have any ideas for me?

I don't know if you've tried this but in case you haven't, Sheldon Brown suggests a technique for getting the chainring well centered on the spider:

http://www.sheldonbrown.com/fixed-conversion.html#chainline

Even if you do get a new chainring (which is probably a good idea anyway), this technique should still be useful.

Thanks,

I did do as Sheldon suggested to no avail.

I am not sure that replacing the chainring will fix my problem, but it won't hurt. Besides, the ring is so worn that it is probably stressing my chain.

In the event that anyone is still following this thread.....

I bought a lightly used 42T 144BCD chainring at the Palmer Swap Meet yesterday.

This did NOT fix my chain tension problem. I should have suspected that it would not.

I must have either a bent bottom bracket spindle or out-of-round cranks.

I have an old crank that I can try, but I need to get a crank puller before I can get the suspect crank off the bike.



BTW:

Many good deals on used stuff to be found at the Palmer MA swap meet. I will be sure to go again next year.

Spot - unless you are dropping the chain, don't worry about it. No chainring is perfectly round. Sheldon's advice (listed above) is a help, but as you have noticed, won't always correct the problem 100%.

Here's what to do: Engage Sheldon's proceedure. When you feel you've done the best you can, find the spot where the chain is tightest, pull the rear wheel back to snug things up and tighten up your rear wheel. Go ride and have some fun. Your chain should not be loose enough to worry about. My fixed gear is like this and I've never lost the chain. Just make sure your chainline is right.

update:

I bought a crank puller and installed a different crank arm on the drive side.

The problem still exists, the chain is slack in exactly the same segement of the stroke.

I now believe that my bottom bracket spindle is bent. Just to be sure, I will remove both crank arms, and replace rotated 180 degrees on the crank spindle. If my theory is correct, the slack should occur 180 degrees from were it is occuring now.

Then I will prob need some more new tools to remove the bottom bracket. :)

It takes finesse and practice to get it right. You have to adjust your chainring according to good old Sheldonbrown's instructions.

it's probably your chainring, they are hardly concentrically perfect.

Exactly how bad is the tension variation? That would answer a lot. If it is a huge variation, then I am guessing the chainring can't be installed THAT far off center.

there will always be some offset. slightly loose is ok if your chainline is straight. don't let any one point bind (if it does, loosen more). a new/quality chainring WILL help resolve this

Yeah just get it the correct tension where it's tightest and "SET IT AND FORGET IT"

Holy necro thread. 6 years old might be a record.