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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 01-07-05, 04:32 PM   #1
wunder
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Cog width, chainline, chainring and tension.

Alright, I've been able to deal with it for the past few rides, but it's starting to get on my nerves now.

This is on a Specialized Langster.

When the chain is off, it seems like the chainline should be decent, but the moment I put the chain on...the chainline is obviously not on. It seems as if my chainring is slightly warped, because when I look down while pedaling I notice that the chainring sucks towards the frame a bit, then goes back out. Would this be affecting my ability to get decent tension on the chain as well? Is it time for a new chainring?

The cog I am using is 3/32". Which is skinnier than the freewheel that came on the bike, which leads me to believe that I should've got a 1/8" cog instead?

I've been searching the forums and toying with my bike all afternoon and I am starting to get bummed out.
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Old 01-07-05, 05:46 PM   #2
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Do you still have the freewheel? If so, measure the difference in shoulder to teeth distance between the freewheel and cog. That's the difference in chainline.
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Old 01-07-05, 06:37 PM   #3
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If the ring is wobbling back and forth it's either loose, the cranks are loose, or the ring is bent. The first two will give you noticeable play in the drivetrain. For the latter you can straighten it out and make it better though it'll probably never be perfect. I believe there was a thread in the mechanics forum a while back about the many ways to straighten a chainring.
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Old 01-08-05, 02:21 AM   #4
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Quote:
Originally Posted by BlastRadius
Do you still have the freewheel? If so, measure the difference in shoulder to teeth distance between the freewheel and cog. That's the difference in chainline.
!!!!

The freewheel's teeth sit like a shade over 1/4", where as the center of the cog's teeth sit just a shade below 1/4".

So do I just put an appropriately sized spacer between the hub body and the cog?
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Old 01-08-05, 02:28 AM   #5
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If you could find an appropriately sized spacer and there are enough threads on the hub body for all the cog threads to screw onto with the spacer, that would work. Does the hub have the reverse threaded lock ring threads?
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Old 01-08-05, 02:39 AM   #6
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Quote:
Originally Posted by BlastRadius
Does the hub have the reverse threaded lock ring threads?
Yes.
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Old 01-08-05, 12:06 PM   #7
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Addiding to what I said above, another possibility is that your crank spiders are bent. If you're really seeing some lateral eccentricity in the chain ring I would focus on that first and foremost. You won't ever get a consistently straght chainline if the ring doesn't stay put.

Tighten your stack bolts. Check the cranks for wiggle. Take the ring off the spiders to see if it can lay flat. If there is no wiggle and the ring is flat but the wobble continues then your spider's probably bent.

Oh, and 3/32 is smaller than 1/8.
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Old 01-08-05, 12:32 PM   #8
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Quote:
Originally Posted by bostontrevor
If the ring is wobbling back and forth it's either loose, the cranks are loose, or the ring is bent. The first two will give you noticeable play in the drivetrain. For the latter you can straighten it out and make it better though it'll probably never be perfect. I believe there was a thread in the mechanics forum a while back about the many ways to straighten a chainring.
yes, you can straighten a chainring fairly easily, although it's true it won't be perfect and it can be tedious. with the bike in a stand, take the chain off and look down over the chainring. spin the pedals and find where the "peak" of the bend is (look at the distance between the down tube and the edge of the ring as you spin). use an adjustable wrench (sized to fit easily over the chainring) to bend it the other direction at that spot. bend it little by little, not all at once, continually checking to see if the chainring is straight. another option is to hit it with a hammer, although i usually only do that if it's only a few teeth that are bent, and i reccomend using a large punch in that case. the guys at my shop do this. good luck

ps: you can also do this with disc brake discs, especially on cheaper ones that usually aren't "true"
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Old 01-08-05, 01:08 PM   #9
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Alright, I went and messed with it some more and here's what I found...

When taking the chainring on/off the spider I noticed I had to kind of "muscle" it on and off. It wouldn't just come loose when the stack bolts were removed, I had to pull it off the spider. Now could this be causing the chainring to warp in that certain spot, due to the un-needed tension?
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Old 01-08-05, 01:51 PM   #10
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Only if that unneeded tension were the result of the spiders being bent. That in and of itself won't be the problem. Lots of rings don't sit entirely cleanly on the landings, no big.
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Old 01-08-05, 02:18 PM   #11
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Quote:
Originally Posted by bostontrevor
Only if that unneeded tension were the result of the spiders being bent. That in and of itself won't be the problem. Lots of rings don't sit entirely cleanly on the landings, no big.
Thanks for the help. I'll work with the chainline today and then go from there.
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Old 01-08-05, 02:41 PM   #12
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Quote:
Originally Posted by BlastRadius
If you could find an appropriately sized spacer and there are enough threads on the hub body for all the cog threads to screw onto with the spacer, that would work. Does the hub have the reverse threaded lock ring threads?
Well, I got the lockring off, and not all of the cog threads screw on to the hub body without the spacer...so I guess the spacer idea is out. And I threw the spacer on the outside of the cog just to see if I could still get the lockring threaded on. I could, but there weren't a whole lot of threads holding it on.

So I need to somehow bring the chainring "in" to get the chainline centered.

Last edited by wunder; 01-08-05 at 03:46 PM.
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Old 01-08-05, 04:31 PM   #13
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Chainring spacers or shorter BB are the only options now.
http://harriscyclery.net/site/itemdetails.cfm?ID=681
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Old 01-09-05, 01:51 AM   #14
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Ugh, yeah...BB

I found this post just a bit ago:

Big Difference?
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Old 01-09-05, 02:01 AM   #15
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http://www.businesscycles.com/trcomp2.htm

look at the bottom of page.




S/F,
CEYA!
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Old 01-09-05, 10:21 AM   #16
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Quote:
Originally Posted by wunder
Ugh, yeah...BB

I found this post just a bit ago:

Big Difference?

If the '04 has the same spindle as the '05, it already has a very short BB, 103mm,
so you're unlikely to find a shorter spindled BB. You may have to just use spacers.
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Old 01-09-05, 12:26 PM   #17
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there is also a lot of good info on chainline at http://www.sheldonbrown.com/chainline/
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