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one chain loop
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Discussion Starter · #1 ·
Since most of SS'ers start from DIY's, I added a little instructables on how to achieve the "perfect" chainline. No more guess works and eyeballing so grab that ruler.

The instruction is for SS conversion from geared cassette and having the front chainline as the constant, meaning that the chainring is fixed and the cog will be the one to follow/adjust.

1. Measure your front chainline. This is the distance between the center of the frame/tube and the chainring. It's a bit tricky to find the center of the frame, look for bottle mounts. I gave mine as an example, 50mm.


2. Measure your rear hub spacing. Most mountain bikes have 135mm rear hub spacing, when in doubt, measure from locknut to locknut. Image courtesy of Sheldon Brown.


3. Reminisce grade school.

135mm / 2 = 67.5mm, this is your imaginary center of your rear spacing.

I think you know what next. Subtract your front chainline to the center of rear spacing.

67.5 - 50 = 17.5mm

17.5mm is your "perfect chainline", measure this from your locknut to your hub similar to figure 2. Take note that the center of the cog must fall into this measurement.

Congratulations! I promise you that there will be no more skipping, no more guessing, no more headaches.

4. Congratulate yourself with a bottle of beer or two.:thumbsup:
 

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Too logical. I prefer the SWAG approach. Nothing beats slamming your chest into the stem or knee into the stem when you chain jumps off the cog... :)

Great instructions. Woulda been handy when I first started SSing.
 

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Made in Canada
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This'll be VERY useful for me... well that is if my parts order ever comes in for my conversion...:skep: ... Thanks! :D
 

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One prob with this idea: As tension pulls on my chain tensioner, the sprocket on the tensioner is not perfectly perpendicular (90 deg.) to the ground so my line is always off. Whats the best way to make my SS the most efficient?
 

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one chain loop
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Discussion Starter · #8 ·
flankwood said:
One prob with this idea: As tension pulls on my chain tensioner, the sprocket on the tensioner is not perfectly perpendicular (90 deg.) to the ground so my line is always off. Whats the best way to make my SS the most efficient?
i guess you have a bent derailleur hanger, its either replace it or straighten it back to normal.
 

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one chain loop
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2,360 Posts
Discussion Starter · #12 ·
67.5 Rule

Here's a quick tip to check whether your chainline is correct or not. Let's call it the 67.5 rule. 67.5mm is your number if you have 135mm hub spacing, 60mm if you have 120mm etc... you know the drill.

This instruction will take you less than a minute to do.

1. Measure front chainline. Center of the frame to middle of chainring. My example: 50mm



2. Measure rear chainline. Middle of cog to where the locknut of axle and frame touches. Mine: 17.5mm



3. Add the two measurements and it SHOULD be 67.5mm

4. Adjust cog/chainring accordingly to achieve your 67.5 number.

5. Celebrate and get drunk.
 

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Or the inveterate bodgers method....

Put the cog on the cassette without any spacers. Put on the chain. Turn the cranks a few times with a bit of drag from the brakes to put tension on the chain.

This will put the cog in the optimum position. Mark the cassette around the cog with a pencil. Add spacers to suit.

That's it. Perfect spacing.
 

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one chain loop
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Discussion Starter · #14 ·
Velobike said:
Or the inveterate bodgers method....

Put the cog on the cassette without any spacers. Put on the chain. Turn the cranks a few times with a bit of drag from the brakes to put tension on the chain.

This will put the cog in the optimum position. Mark the cassette around the cog with a pencil. Add spacers to suit.

That's it. Perfect spacing.
never thought of that, i guess mine is the anal method. :D
 

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on my current project......I have not gotten to this point yet....what if I have the screw on/bolt on rear wheel....do I add a spacer to the rear and then screw on the free wheel or will it be perfect?
 

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Keep on Rockin...
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I get chain drop often if I have a perfectly straight line. Power to the pedal pushes the BB "inward" away from the pedaling leg. Running my rear cog slightly inboard significantly alleviates the frequency of chaindrop on most of the SS frames I've owned.
 

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Just got my new Truvativ Noir 1.1 and wanted to make sure my chainline was right using the measurement method described above and turns out my cog was outboard the width of a 5mm spacer. My hubs are SS specific and only came with three spacers all 5mm so I knew I didn't have many options when I first set it up on the stylo 1.1 crankset. I ran that for a few hundred miles with my imperfect chainline. What I noticed on the aluminum bash ring from the stylos were tiny scrapes a various intervals around the edge, I assume from the chain nicking them when under heavy load and frame/bb deformation. I fixed it up so it's dead on by only swapping my Chris King stainless cog inboard a 5mm spacer and now everything measures up. 50mm from center of seat tube to chainring and 17.5mm from cog teeth to outside edge of the hub. I always thought it looked pretty straight before but now I know it's straight and it doesn't seem to make the chain track slightly to the outside of the front chainring like before. Glad I checked as the chain would have eaten up the carbon bash ring faster then the aluminum one I had.
 
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