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Old 10-23-08, 05:43 PM   #1
Autobus
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Who makes the roundest chainrings?

I hate when the chain slackens/unslackens on my fixie due to my sucky rocket chainring

Who has a rep for making quality, round chainrings?
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Old 10-23-08, 06:01 PM   #2
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What you want are Shimano Biopace chainrings.
Just the thing for a fixie.

"People are often astonished to learn that I ride Biopace chainrings on fixed-gear bikes. They imagine that there will be tremendous changes in chain tension as the chainring rotates. In practice, this is not the case. A 42 tooth chainring will generally engage 21 teeth against 21 chain rollers, regardless of its shape.

There is a slight variation in tension resulting from the varying angle between the two straight runs of chain as the axis of the chainring rotates, but this has not generally been of a sufficient magnitude to cause any problem in practice for me."
Sheldon Brown.

If Sheldon didn't have troubles with Biopace you shouldn't have trouble with round Rocket Rings.
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Old 10-23-08, 06:15 PM   #3
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Does the slackening happen when you pedal lightly with the bike in a stand? If not, maybe frame flex is the problem.

I hope my rocket ring is round, I just got it to replace a Biopace... on a derailleur-having bike, however.
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Old 10-23-08, 06:19 PM   #4
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expensive track rings. Any ring made for use with a derailleur need not be all that round.

But then, a certain amount of unroundiness is really not a problem.

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Old 10-23-08, 06:42 PM   #5
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Are you sure you have it centred just right on the crank?

I usually have to play around with this to get it right. Sheldon has a method on his site somewhere.

Basically you have the bolts finger tight, mount the rear wheel, rotate the crank until the chain is at the tightest point and tap the chain to move the chainring a bit, keep doing this until there is no tightest point.
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Old 10-23-08, 06:44 PM   #6
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this is just my experience. but so far sugino mighty comps are very round. suntour superbe pro are also very good. shimano 105s not so much. shimano 600s aren't bad.
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Old 10-23-08, 07:05 PM   #7
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Are you sure you have it centred just right on the crank?

I usually have to play around with this to get it right. Sheldon has a method on his site somewhere.

Basically you have the bolts finger tight, mount the rear wheel, rotate the crank until the chain is at the tightest point and tap the chain to move the chainring a bit, keep doing this until there is no tightest point.
That's what I think too. Get your chainring concentric with the BB spindle and your problem will go away.

I can't imagine anyway of manufacturing a chainring that would result in out-of-roundness sufficient to cause chain tension problems.
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Old 10-23-08, 07:14 PM   #8
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Gee, they all look pretty much round to me. The round ones, anyway.
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Old 10-23-08, 07:50 PM   #9
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Originally Posted by top506 View Post
What you want are Shimano Biopace chainrings.
Just the thing for a fixie.

"People are often astonished to learn that I ride Biopace chainrings on fixed-gear bikes. They imagine that there will be tremendous changes in chain tension as the chainring rotates. In practice, this is not the case. A 42 tooth chainring will generally engage 21 teeth against 21 chain rollers, regardless of its shape.

There is a slight variation in tension resulting from the varying angle between the two straight runs of chain as the axis of the chainring rotates, but this has not generally been of a sufficient magnitude to cause any problem in practice for me."
Sheldon Brown.

If Sheldon didn't have troubles with Biopace you shouldn't have trouble with round Rocket Rings.
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Old 10-23-08, 07:51 PM   #10
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Originally Posted by Autobus View Post
I hate when the chain slackens/unslackens on my fixie due to my sucky rocket chainring

Who has a rep for making quality, round chainrings?
It's not just about the chainring. It's also the crank, bb, rear hub and cog. This combo has no variation in chain tension -

Dura ace track crank + Dura ace BB + Phil wood rear hub + phil wood cog.
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Old 10-23-08, 07:53 PM   #11
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Originally Posted by Retro Grouch View Post
That's what I think too. Get your chainring concentric with the BB spindle and your problem will go away.

I can't imagine anyway of manufacturing a chainring that would result in out-of-roundness sufficient to cause chain tension problems.
He didn't say it was a problem. My guess is that the normal vairation in chan tension with shyzor components is making the OP cocerned. All he needs to learn is that if the tension variation is not great enough to be bind/loose enough to fall off the ring then it's fine.

"centering the chainring" on the spider sometimes helps and most of the times doesn't.
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Old 10-23-08, 08:00 PM   #12
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Originally Posted by LesterOfPuppets View Post
If not, maybe frame flex is the problem.
This has nothing to do with chain tension variation.
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Old 10-23-08, 08:21 PM   #13
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He didn't say it was a problem.
Oops, you're right.

I can't imagine any way of manufacturing a chainring that would result in out-of-roundness sufficient to cause chain tension issues.

Happy now?
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Old 10-23-08, 08:34 PM   #14
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I can't imagine any way of manufacturing a chainring that would result in out-of-roundness sufficient to cause chain tension issues.
I'll have to agree with this. But a borderline whacked out chainring with crappy crank/bb/cog combo in total may be sufficent enough to cause problems.
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Old 10-23-08, 08:37 PM   #15
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I am partial to Sugino chain rings... even their road rings are remarkably true (for lack of a better term) and with a good crank they provide really consistent chain tension on ss and fixed gear bikes.

Stronglight and TA also make incredibly nice chain rings.

I am also a fan of Biopace rings on ss and fixed gear bikes as they do work really well and my longbike also uses them for that extra bit of torque it needs for climbing when it is loaded with 100 plus pounds of stuff.

I have not been as pleased with Surly ss chain rings as they seem to have a lot of variance.
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Old 10-23-08, 09:59 PM   #16
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Geez, is it just me, or is everyone here missing the intent of the OP's question (it's a little vague)?

When you do the chain tensioning adjustment on a BMX, or fixie, or single speed, you try to find the "tight" position of the chainring and then lock down your axle nuts with the rear wheel pulled as tight as you can get it. It's always going to loosen a little bit when you tighten the drive side nut. That way, when the chainring allows the chain to go to the "slack" position, it's as minimally slack as you can get it.

By searching for "round" chainrings, I am assuming that the the OP is looking for a more uniform chain tension throughout the rotation of the chainring. I can see where this could be important to a really critical rider.

OK, to address the OP's original question ...

I'd say that the difference between "tight" and "slack" on almost all chainrings is soooooo small (as far as the roundness of the chainring goes) that, to get it rounder", it would cost a tremendous amount (i.e. = machine shop precision and the accompanying price).

So, I'm kind of shooting in the dark here, as I don't know the full intent of the original question.

Comments? OP? others? It IS an interesting question.
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Old 10-23-08, 11:19 PM   #17
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I actually thought I should say something about biopace after reading the OP, firstly to be funny (and yeah, I do find it funny) and secondly because they actually do work on fixies, as counterintuitive as it seems.

In my experience, making sure the chainring is centered on the crank spindle is the biggest deal. I've had to carefully work on this with two bikes - because there is some play when you mount a chainring on a crankarm, before you tighten it down. And this can place teeth on one side further away from the axis of rotation.
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Old 10-24-08, 12:47 PM   #18
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In my experience, making sure the chainring is centered on the crank spindle is the biggest deal. I've had to carefully work on this with two bikes - because there is some play when you mount a chainring on a crankarm, before you tighten it down. And this can place teeth on one side further away from the axis of rotation.
Yeah, the hole in the crankarm is larger than the chainring bolts. If you install a chainring bolt/nut into a crankarm without any chainring, you can feel that there's a lot of radial-play available. If you identify the high-spots on the chainring, you can loose all the chainring bolts slightly and tap the chainring down slightly in that spot and tighten the bolts. Basically "truing" a chainring by centering it over the BB-spindle.

I wonder what problem the OP has that makes him think that the roundness of the chainring is the cause?
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