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PSYCHOLUST
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485 Posts
Discussion Starter · #1 ·
I don't know how most of us would determine positioning rings and spacing cogs to get a perfect chainline, but I had used the "One-eye -closed, look-down-past-the-top-tube" method until I recently became curious as to how accurate such a method might be.

I'm sure alot of you have, at some point, been riding behind another SS or checked one out on a roof rack at a trail head and thought,

" That's one crazy looking chainline."



So I decided to check my own work in a more scientific way and found my ONE-EYED method to be surprisingly inaccurate.

So I came up with this......

1)Measure BB shell ( 68mm or 73 in MOST cases )

2)Apply masking tape to bottom of shell and mark the center (34mm or 36.5mm from one side)

3)Using a set-square,( set against the center mark on the BB shell) Measure the distance to the center of the chain ring teeth and write down the measurement . ( eg 55mm)

4)Determine the rear hub spacing of your frame ( 135mm in MOST mtb cases) With 135mm hub spacing, that puts the inside face of the right drop out 67.5mm from center

5)Simple MATH… 67.5mm – 55mm = 12.5mm

6)Using spacers you would position your rear COG’S CENTER 12.5mm from the end of your HUB or the inside edge of your right drop out.
( in a case of a wide based cog, like a Chris King, Niner or Surly measure to the center of the teeth, not the edge of the cog

Note: If, by chance, I am the last guy on the planet to figure this out and EVERYONE has been doing this all along, Be gentle in your flaming.
 

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one chain loop
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2,360 Posts
thanks Tone, actually three years ago I made a thread very similar to scyule. but scyule's approach is better since he actually marked the center of the bb shell rather than me eyeballing the center of the seat tube. using the mounting holes for the bottle cages as a reference works too, if there's any.

http://forums.mtbr.com/singlespeed/perfect-chainline-426690.html
 

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483 Posts
for chainline up front, i'd rather work from the seat tube. measure seat tube diameter with calipers.

chainline = chainring to seat tube distance + 1/2 diam of seat tube
 

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+1 for sticky.

I just converted my A9C over to SS and aligned everything via a straight edge. I was close, but now I'm dead on. Great job to both of you :thumbsup: and +1 for making this a sticky. I read both, but used the ruler/math version.
 

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92 Posts
I went for a ride today and wanted to post a follow up. The first two rides, I dropped my chain three times. After using the method previously mentioned, I did not drop the chain at all. Thanks again guys.
 

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I've been dealing with chain line issues since I started changing around my gearing.
I like to ride w/o a chainguard for the look of the singlespeed chainline. The chain popping off from the chain tension slipping, the bushings in the chain deforming, or from just being to loose from my own adjustments on top of the chainline.

I just ended up taking a 2 ft level and squaring it up against my chainring and go like that. I think I've got it down to around 1/64th of an inch off in either direction with the spacers I am using.

It's a surly cog offset with the flat side out and a 2.5mm alum spacer with a very thin metal spacer. The thin metal spacer is about double the thickness to make it spot on to my eyes.

I am unsure if I will get fanatical enough to get it exact.


I also sourced out a KMC K810SL chain, was a total PITA....Only like 4 online retailers carry this thing. It's a 3/32 singlespeed specific lightweight chain.
I wanted to spring for the ti coat but bought two nickel coated instead.

I hope the new chain and chainline holds up well. I am able to stretch 9speed chains in what the LBS tells me is way sooner than they should be wearing.
 

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346 Posts
the post I'm waiting for:

What about this:
I buy a rear SS hub, threaded for freewheel. I thread on a freewheel. I have a SS crankset, but now I need a BB. How do I figure out the spindle length without returning 2 BBs?

Anyone?
 

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346 Posts
any and all.

It's the spindle length that always hangs me up, not the spacing of the cog on a freehub. Anyone using a freehub has got it easy. Since this is a sticky, it should cover chain line in as many situations as possible, IMHO.

love,
10speed
 

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singletrack bound
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3,134 Posts
Not if I have 10 bikes sucka!

jk, It actually refers to a prank call I made to the LBS, that I was working for. I told "Someone called me and said my part was in, you got it or what? It's a ten speed biopace freewheel." The kid was clueless.

thanks for asking.
OK......

now that we know the story behind your screen name.....

it's cool....

carry on....

in the SS forum.....

:D
 
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