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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 10-14-06, 09:25 AM   #1
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Chainring roundness (newb)

Have enjoyed building and riding my fixie conversion (and on a trackstand* it makes a great stationary bike too). I followed Sheldon Brown's loosen-the-chainring-bolts-and-tap-the-chain routine for getting the chainring concentric but, try as I might, I can't get the chain tension totally even - better, yes, but not perfect. I know, futz with how tight or loose the bolts are, etc. But still...

So, how "perfect" does it have to be? Hints and tips? Yes, the chainring itself is fine.

I'd just ask Sheldon but with his recent health issues he has bigger things to worry about I'm sure.

----

*Edit: I meant a trainer.

Last edited by bcoppola; 10-14-06 at 01:42 PM.
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Old 10-14-06, 09:54 AM   #2
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You probably won't be able to get it "even" but I wouldn't worry about it unless the chain is falling off. Spin the wheel to the point where the chain is the most slack and adjust the chain tension from the dropouts at this point.
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Old 10-14-06, 10:00 AM   #3
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totally even is very tough, as paule said. I try to just get the tightest point set so that's where my crank is when I trackstand on the street (usually L forward for me), that's the only time you're ever really going to know the difference between good enough and really freakin' perfect.
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Old 10-14-06, 10:38 AM   #4
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sheldons lying with that tap the chain ****. it's never worked at all for me.
what you don't want to do is over tighten your chain, to the point where it's loud as hell and actually slows down your momentum. my chain at it's slackest point has about half an inch or so of play. you don't notice any real sag, but you can move it around by hand. not an issue.
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Old 10-14-06, 01:42 PM   #5
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Thanks. Judging from the responses my chain slack is not enough to worry about. The bike rides very nicely.

But...can an old guy teach himself to do a trackstand without breaking bones??
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Old 10-14-06, 04:25 PM   #6
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Originally Posted by bcoppola
Thanks. Judging from the responses my chain slack is not enough to worry about. The bike rides very nicely.

But...can an old guy teach himself to do a trackstand without breaking bones??
You can teach yourself. Set your saddle a couple centimeters lower, don't use cleats or clips, and raise your bars if you're able to. Be sure it's a fixed gear to start with and don't get acclimated to adjusting with handbrakes -- just use your legs.

As for chain tension, some chainrings are more round than others but almost all are pretty bad. I've had significant out-of-roundness with Campy, Dura Ace, and all the rest. The best I've found have been the true Zen chainrings (144 BCD version in silver). Why there should be any eccentricity in a chainring is beyond me, what with modern milling practices, but at least part of the problem is in the crankarm itself. You don't want excessive chain slack (not much more than about an inch of vertical movement in the chain when the pedals are slack) nor excessive tightness (less than half an inch of movement, and no grinding or rattling noise while riding). If you have new equipment and it's really out of round, return it. If you have used equipment, since it's a good bet that both chainring and crankarm need help, just rotate the chainring a couple holes and reattach it. You may find that it improves matters (or makes them much worse); just find the best position. You may feel slack tension a bit more when you're trackstanding, but it's just a matter of feel -- what's more important is keeping tension as even as possible while you're actually pedaling. The consequences are a thrown chain or a broken one, and those are both bad events on a fixed gear.
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Old 10-14-06, 05:46 PM   #7
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when you guys are talking about an "inch and a half" of movement, is that side to side or up and down
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Old 10-14-06, 05:55 PM   #8
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Up and down.
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Old 10-14-06, 06:49 PM   #9
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But...can an old guy teach himself to do a trackstand without breaking bones??
Oh, if you're concerned about falling it helps to do it on grass (golf course, not the other kind, though both create a kind of slow motion while you're learning).
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Old 10-14-06, 06:54 PM   #10
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east point, represent.
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Old 10-14-06, 07:35 PM   #11
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east point, represent.
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Old 10-14-06, 10:09 PM   #12
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Originally Posted by 11.4
You can teach yourself. Set your saddle a couple centimeters lower, don't use cleats or clips, and raise your bars if you're able to. Be sure it's a fixed gear to start with and don't get acclimated to adjusting with handbrakes -- just use your legs.

As for chain tension, some chainrings are more round than others but almost all are pretty bad. I've had significant out-of-roundness with Campy, Dura Ace, and all the rest. The best I've found have been the true Zen chainrings (144 BCD version in silver). Why there should be any eccentricity in a chainring is beyond me, what with modern milling practices, but at least part of the problem is in the crankarm itself. You don't want excessive chain slack (not much more than about an inch of vertical movement in the chain when the pedals are slack) nor excessive tightness (less than half an inch of movement, and no grinding or rattling noise while riding). If you have new equipment and it's really out of round, return it. If you have used equipment, since it's a good bet that both chainring and crankarm need help, just rotate the chainring a couple holes and reattach it. You may find that it improves matters (or makes them much worse); just find the best position. You may feel slack tension a bit more when you're trackstanding, but it's just a matter of feel -- what's more important is keeping tension as even as possible while you're actually pedaling. The consequences are a thrown chain or a broken one, and those are both bad events on a fixed gear.

aren't the sugino s3 cubic and gigas rings guaranteed to be milled to a tolerance of 0.05mm?
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Old 10-14-06, 10:15 PM   #13
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aren't the sugino s3 cubic and gigas rings guaranteed to be milled to a tolerance of 0.05mm?
Doubtful...do you realize how incredibly tight that would be? I think the majority of cost comes from the hand finishing and alloys used, not necessarily the machining. Hell, why wouldn't they just make all of their chainrings round if all they had to do was press a button?
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Old 10-15-06, 12:13 AM   #14
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Doubtful...do you realize how incredibly tight that would be? I think the majority of cost comes from the hand finishing and alloys used, not necessarily the machining. Hell, why wouldn't they just make all of their chainrings round if all they had to do was press a button?
actually, I just got my S-Cubic today, and the piece of paper that came with it, although all in Japanese, has a bar graph that shows "S-Cubic" at 0.05 micrometers, and something else (in Japanese) at 0.50 micrometers. maybe it's referring to roundness?
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Old 10-15-06, 01:30 AM   #15
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0.5mm is the J.I.S. standard for runout. as i understand it, runout is the deviation between the rotational centerline of the chainring (crank spindle) and the rotational centerline of the teeth. all the tips of the teeth teeth should be equidistant from the center, but they can be up to 0.5mm off. the s3 and gigas are machined to a tenth of that. based on my limited understanding of machining, i'd say that the machinery and bits have to be capable of a certain tolerance, and the ones capable of doing 0.05 are more expensive than the ones that can do 0.5. i'm reasonably sure that the bits have a shorter lifespan, and that the machining process takes waaaay longer.

i'm pretty sure that sugino rings break down like this:

75 - $76.50
- 7075 t6 aluminum
- machined to 0.5mm tolerance
- bead blasted

zen - $87.50
- 7075 t6 aluminum
- machined to 0.5mm tolerance
- W-cut teeth
- relieving on the back

s3-cubic - $110
- 7075 t6 aluminum
- machined to 0.05mm tolerance
- bead blasted
- s3 smooth coating applied via electrochemical dip

gigas - $325
- high grade proprietary gigas alloy
- machined to 0.05mm tolerance
- bead blasted
- s3 smooth coating applied via electrochemical dip
- teeth hand finished
- chainring is fully polished

however, last time i had exchanged emails with john from business cycles, he didn't have any information on the machining tolerances for shimano, campy and the like. that said i'm still crossing my fingers that phil wood will come out with track chainrings someday.

Last edited by sers; 10-15-06 at 01:36 AM.
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Old 10-15-06, 07:24 AM   #16
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(snip)...
gigas - $325
- high grade proprietary gigas alloy
- machined to 0.05mm tolerance
- bead blasted
- s3 smooth coating applied via electrochemical dip
- teeth hand finished
- chainring is fully polished...(snip)
Sounds like just the thing for my $10 thrift shop conversion!

My chain slack at worst is no more than 1/2" and the drivetrain doesn't bind at its tightest so I'm good to go. And trackstanding would be fun but is actually low on the list of reasons I'm trying a fixie.

Hey, until this summer my only bike was the Trek 7200.

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Old 10-15-06, 08:36 AM   #17
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Do you have a chainring bolt tool? They cost about $3 and grip onto the back of the bolt so that you can really tighten them. You might want to try that too...Also, try tightening the bolts like you would on a car wheel (as reccomended by Sheldon Brown).

Here's one on nashbar, but your LBS probably has one.
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Old 10-15-06, 09:46 AM   #18
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your inability to trackstand has nothing to do with the roundness of your chainring.
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Old 10-15-06, 09:46 AM   #19
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I got a 48 tooth biospace that seems a little out of round.
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Old 10-15-06, 10:08 AM   #20
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Quote:
Originally Posted by rustang
your inability to trackstand has nothing to do with the roundness of your chainring.
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Old 10-15-06, 10:23 AM   #21
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Quote:
Originally Posted by bcoppola
But...can an old guy teach himself to do a trackstand without breaking bones??
On non-fixies, you need an uphill slope to do a trackstand: pedal forward, roll back. I learned using a wheelchair ramp...rails on both sides to grab onto as you practise. This may not apply to fixies.
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