# Sticky  CHAINLINE math



## scyule (Nov 8, 2009)

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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## Tone No Balone (Dec 11, 2004)

*chainline for dummies.....*

http://forums.mtbr.com/singlespeed/why-does-happen-736137.html


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## fishcreek (Apr 10, 2007)

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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## fishcreek (Apr 10, 2007)

i think this thread should be stickied. :thumbsup:


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## scyule (Nov 8, 2009)

Wow, the SKEWER METHOD is a thing of beauty.


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## Cygnus (Jan 7, 2004)

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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## jeremy524 (Jul 17, 2010)

*+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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## jeremy524 (Jul 17, 2010)

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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## iridetitus (Sep 16, 2004)

so, wait.....chain line matters?


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## fishcreek (Apr 10, 2007)

no. balls matters. or a ball, whatever is left.


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## Cygnus (Jan 7, 2004)

iridetitus said:


> so, wait.....chain line matters?


yes it does.

of all the reasons to ride SS or fixed, a perfect chainline is the 1st that comes to mind.


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## Node (Aug 12, 2008)

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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## scarkinsmel (Mar 18, 2004)

I like it. Thanks for making it sticky and even if it has been done, who cares? Good info is good info.


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## ancient rascal (Mar 2, 2010)

fishcreek said:


> no. balls matters. or a ball, whatever is left.


+ 1


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## 10speedbiopacefreewheel (Aug 19, 2008)

*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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## fishcreek (Apr 10, 2007)

what kind of cranks?


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## 10speedbiopacefreewheel (Aug 19, 2008)

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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## Tone No Balone (Dec 11, 2004)

oxymoron 

10speed/singlespeed?

no?


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## 10speedbiopacefreewheel (Aug 19, 2008)

Tone No Balone said:


> oxymoron
> 
> 10speed/singlespeed?
> 
> no?


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.


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## Tone No Balone (Dec 11, 2004)

10speedbiopacefreewheel said:


> 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.....


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## 10speedbiopacefreewheel (Aug 19, 2008)

Tone No Balone said:


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


thats right guy. My screen mocks the over complication of drive trains. I have 5 bikes right now: 3 SS, a 1x7 with friction shifting and a 3x9 friction. WHAT NOW!? say something! hahaha jk.


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## Tone No Balone (Dec 11, 2004)

10speedbiopacefreewheel said:


> thats right guy. My screen mocks the over complication of drive trains. I have 5 bikes right now: 3 SS, a 1x7 with friction shifting and a 3x9 friction. WHAT NOW!? say something! hahaha jk.


but are any 29er's?


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## 10speedbiopacefreewheel (Aug 19, 2008)

Tone No Balone said:


> but are any 29er's?


no. I tasted the kool aid and spit it out.


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## pursuiter (May 28, 2008)

Here's how I measure crank chainline:

1.) Measure seat tube diameter and divide by two.










Then measure from the far end of the seat tube to the middle of the chainring (in this picture I am off slightly due to bad picture taking skills, the caliper should measure to the middle of the chain, not the edge):










Then subtract the first measurement (1/2 the seat tube diameter) from the second measurement and you have the chainline.


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## TruTone (Jun 30, 2011)

I would like to add, and this is rather random information, that older triple cranks like Sugino ATs have a chainline, with properly sized bottom bracket, that lines up the outer ring more or less perfectly with a disc-mounted fixed gear cog with no spacers. This setup will allow a fixed/free setup on a disc brake freehub with a properly spaced cog and spacer set on the freehub side. Running this setup with a VeloSolo 3/32" cog and a 9 speed chain, I have had absolutely no problems with chain drop in fixed and free modes. Also, there is a possibility with these cranks to run an additional ring on the front and a more inboard cog on the freehub for a second gear ratio. However this can't be done with another fixed cog, as the cog is already flush with the hub shell.

Advantage being that Sugino AT cranks are vintage, clean, cheap and relatively easy to find on the secondhand market. They are very sturdy, and paired with a cartridge bearing bottom bracket, very low maintenance, near-zero drag and relatively average weight. With my Shimano M475 hub, the setup is dead silent when freewheeling.

Picture included for visual demonstration. Rear cog is a 17t VeloSolo and the front ring is a 36t Sugino. There is a 18t on the freehub side.


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## fishcreek (Apr 10, 2007)

TruTone said:


> older triple cranks like Sugino ATs have a chainline, *with properly sized bottom bracket*, that lines up the outer ring more or less perfectly with a disc-mounted fixed gear cog with no spacers.


nice conversion. but like you said "with the properly sized bottom bracket" is always the question for rear chainlines that is not adjustable (i.e. fixed, freewheel).

and to answer 10speedbiopacefreewheel's question, there is a database of chainline for specific cranks from guru Sheldon Brown (mostly older cranks though):

Sheldon Brown's Bottom Bracket Size Database

i don't really own enough cranks here to measure and figure out crank chainline. even if i did, it will be tricky because you have a variable spindle length on the drive side according to bottom bracket models and manufacturers.


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## TruTone (Jun 30, 2011)

fishcreek said:


> nice conversion. but like you said "with the properly sized bottom bracket" is always the question for rear chainlines that is not adjustable (i.e. fixed, freewheel).
> 
> i don't really own enough cranks here to measure and figure out crank chainline. even if i did, it will be tricky because you have a variable spindle length on the drive side according to bottom bracket models and manufacturers.


I will measure the bottom bracket next time I get to my bike and get back to you on that. It looks like it's a rather long spindle length, which may be difficult to find with modern bottom brackets, but really, the cranks only clear the chainstays with the suggested length. My point being, the cranks work stock (if you happen across a bb/crank combo by itself or on a bike) with the configuration in an aesthetically pleasing manner. :thumbsup:


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## SpryIP (Nov 8, 2011)

Used Pursuiter's method. Perfect!

Thanks


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## bourdlay (Mar 28, 2012)

post


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## cheepnis (Aug 26, 2005)

*Skewer Method.. needs improved*

I like the Skewer Method, but I think eyeballing the skewer over top of the rear drop out can introduce some error. If your eyeball is not directly over the drop out line then the 3 or so vertical inches from the chain down to drop-out will multiply this error.

Would it be possible to improve the rear cog measurement by tightening a piece of something flat and rigid between the frame and hub. Something that won't bend and would bring the measurement up to the chain and square with hub nut.


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## Ponsoldt (Dec 12, 2011)

I see a chain guide in the back. Does everyone use them?


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## ZXFT (Oct 17, 2010)

Is a 4mm offset in chain line going to hurt anything? I know some will say it causes premature wear, but is 4 mm's really enough to fret about?


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## rob1035 (Apr 20, 2007)

I prefer the "float" method, since Im not so hot at math...


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## shreddr (Oct 10, 2009)

i built up my CCFSS and eyeballed the chainline. I rode it and the chain stayed on, so I guess it was ok. I put on a new chainring and was eyeballing it again and thought it looked off a little. I remembered this thread and thought "those guys are killing a mouse with an elephant gun!". I got out a 4' straight edge and layed it along the bashguard in line with the chain and then measured the distance to the chain at the chainring and the cog. I was off by 1 spacer and a thin wave washer. It is perfect now and the whole process took about 2 minutes. too many engineers in here......


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## pentlandexile (Jan 4, 2013)

Redid my SS with new crankset and chain today using this method.... Perfect. Thanks for the post.


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## skiinnyboy (Mar 12, 2013)

wow, sweet advice, that made it so simple to get things right, thanks!!!!


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## sdmtb (Mar 27, 2009)

Thanks for posting this, just did this method when setting up my sawyer with a new crankset and it worked perfectly!


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## brotherpaidjo (Jun 17, 2013)

Tried the method last night to realise my eyeballed setup was 5mm off. My Lynskey is dead on now thanks to this post !


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## danorano (Nov 14, 2012)

Or, you can just get a long straight edge, take the chain off your front and rear sprockets, lay the straight edge flush on the front sprocket side facing away from the frame, then rotate the sprocket until the other end goes down towards your rear cog. The perfecet alignment is when the straight edge just touches flush with the outside of the cog. There's a video on youtube showing exactly how this is done.
Check: How to check the chainline on your single speed bicycle or fixie - YouTube


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## nagmok (Jun 17, 2014)

duct tape laser pen atop drive sprocket…swap spacers until cog lights up


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## NordieBoy (Sep 26, 2004)

Straight edge against side of chain ring is the easiest and doesn't hurt your head with numbers.


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## kennderbender (Oct 31, 2015)

The " end of you hub " , do you mean measure in from the lock ring once installed and tightend hand tight ? sorry if sounding like a rookie, because when it comes to bike building... I am. but this method sounds way better than one eye method. I am building ss from vertical dropout Marin and am having some chain slipping. Trying to dial in, you advise would be great wise one


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## yzedf (Apr 22, 2014)

Motion-Pro chain alignment tool for motorcycles. Not sure why the idea never caught on in the pedal world. Too simple I guess...


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## NordieBoy (Sep 26, 2004)

Tried my motorbike chain alignment tool on the mtb.
Now I use the straight edge on the motorbike as well.


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## mouricesimo (Jul 10, 2008)

i have a chain line cker for motorcycle
rule for bicycles is if you want to make a SS - you can


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## retro74 (Jul 30, 2016)

I was a mechanic for 8 years and there are cases where this matters more to me like a road bike where you want lots of silence and we would use 1/2mm or 1mm spacers on the bottom brackets for that. But mountain biking is dirty and we replace parts more often. Super hilly where I live and I am in the bigger cogs in the rear more, so I go a bit inside the center-line on my alignments when I can. The theory is that 50% of your time is high and 50% is low and you are going for the middle. I spend most of my time in the bigger (low-gear) rear cassette cogs.

Here is the FAST trick to get this done and not go nuts measuring. I mean FAST.

Get a steel or aluminum yardstick or just a flat piece of steel stock that will fit between the rear cassette gear spacing.

You are going to wiggle this between the middle rear cogs up to the front center chainring (follow the path of the chain with the flat metal stock). On a 1X setup that chainring is the ONLY chainring up front.

- For 9 speeds, place the flat metal between 4 and 5 and then 5 and 6 The center front chainring should be in the middle of those two.

- For 10 speeds, the center is between 5 and 6

- For 11 speeds, place the flat metal between 5 and 6 and then 6 and 7 The center front chainring should be in the middle of those two.

The metal might flex a little, but you can go slow, calm down the metal flex and see. Flip the metal 180 degrees (bottom edge to top edge) if you think it is not perfectly straight. The middle is the middle of the two if it differs. 

Move your bottom bracket shims as needed, but account for 100% of the space if you go thinner on one side, that means thicker on the other side of the bottom bracket with the torque-tubes used today. There are some torque-tube shims (think thin washers that fit the Torque tube axle) that can be purchased to make up the difference. Your LBS might have what you need for that.


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## NordieBoy (Sep 26, 2004)

What is a rear cassette?


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## retro74 (Jul 30, 2016)

NordieBoy said:


> What is a rear cassette?


LOL... The entire set of rear cogs is sometimes called a _*cassette*_.


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## edubfromktown (Sep 7, 2010)

Somethin that's not on a single speed LOL


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## retro74 (Jul 30, 2016)

Good point. Single speed alignment you have more toys to play with. Even the 9-10-11 speed folks can use spacers between the crankarm spider and the chainring. You need to make sure the bolts are long enough if you use spacers on the spider. Companies like Surly have spacer kits to move the rear cog out. WAY-back in the age of 10 and 12 speed road bikes and early mountain bikes, the rear gears (freewheel now a modern free-hub+cassette) was threaded on and we could put spacers behind those too.

Overall, you have an arsenal of ways to move the rear single speed cog or front chainring spacers or bottom bracket alignment around. Some combination will get you good alignment, lower chain wear, lower chain noise and that hypnotic sewing machine and well oiled sound as you pedal.


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## erichwic (Mar 3, 2004)

Can't one just use a metal straight edge (like a T-square), hold it flush against the front chain/chainring and make sure it's flush with chain at rear cog? If it needs adjusting I just rework my spacers on rear wheel. That's pretty much what I do and haven't had an issue.


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## NordieBoy (Sep 26, 2004)

NordieBoy said:


> Straight edge against side of chain ring is the easiest and doesn't hurt your head with numbers.


Yep...


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## erichwic (Mar 3, 2004)

100%


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## redwarrior (Apr 12, 2007)

Math is your friend but I’m allergic to numbers & simply sight down the top chain run from the rear wheel. In the past though, I built a bike with a freewheel & square taper cranks & had to use the maths to figure out how much to offset the BB with spacers I didn’t yet have.


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## buffet (Oct 7, 2018)

If the wear on the inner side of my chainring is noticeably more than on the outer side, does it mean that the chainring needs to be moved *outwards* to correct the chainline?


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## retro74 (Jul 30, 2016)

It can mean that you favor one side of the rear cog:
- Flat-Lander -- You use the smaller "high" gears most
- Hilly-Lander -- You tend to use the larger "low" gears most

In general, I would say that it indicates a chain-line problem. On my MTB, I use a Shimano XT crank and a OneUp 30t front to get that little bit of extra inside (low gear) offset and the wear is even on the front chainring. 

You can swap around the bottom bracket spacers if you have a threaded BB. Swap left to right or right to left to move the bearing shell. You can get a couple of mm with what I did with a OneUp front chainring (not cheap, just being honest). You can use washers or spacers to move the chainring if you have enough thread on the bolts or you can also get longer bolts to make sure it has thread purchase. You can seek out such spacers for bikes.

Finally, there is that off-chance that you have a frame that was built crooked or miss-aligned. The straight edge idea should line up with the rear cogs forward and rear facing teeth at the same distance (parallel to cogs), it should follow a line. Misalignment could be from a crash, from manufacturing welds or carbon layup or even a badly threaded bottom bracket. Crashes are not rare, but frame build quality is generally great to reasonable on alignment. If you have a carbon frame that is not in alignment, that is a manufacturing defect that you can't correct and your dealer should swap in a replacement frame. In one case, I had to contact the manufacturer, explain that the bike was purchased with the kid's savings from odd-jobs and then they contacted the uncooperative shop that sold him the bike.


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## mack_turtle (Jan 6, 2009)

retro74 said:


> It can mean that you favor one side of the rear cog:


thank you for the detailed response, but you missed the point. this is the singlespeed forum. one speed = one chainring and one cog. buffet is asking if his single cog needs to be moved in or out to correct a chainline that does not line up straight.



buffet said:


> If the wear on the inner side of my chainring is noticeably more than on the outer side, does it mean that the chainring needs to be moved *outwards* to correct the chainline?


it sounds like your cog is pulling your chain to the right, away from the center of the bike. that would put more friction on the inside of the ring. move your cog inward.

better yet, use the simple measurements and basic arithmetic outlined in this thread to take out the guess work.


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## mack_turtle (Jan 6, 2009)

here's my method for freehubs with spacers:
• take the diameter of your seat tube and divide by 2. (example: if you have a 34mm seat tube, the distance to the center of the tube is 17mm.) basic math!
• measure from the right side of the seatube to the center of the chainring teeth. add that to the number above. again, BASIC math. (continuing the example, if the distance is 32mm, 32 + 17 = 49. 49mm is a common mtb chainline for pre-boost setups, so that makes sense.) that is your *chainline*. you want your rear cog to line up with 49mm from the center of the bike.*
•now take the OLD measurement of your hub. on most older mountain bikes, that's either 135 or 142mm. boost would be 148. divide that by 2 to find the center of the axle. that's 67.5, 71, or 74mm by the examples above.
•subtract your chainline from half axle. (if you have a 49mm chainline and a 148mm boost hub, that number is 74-49 = 25.) that is the distance you want to get from the right end of your axle to the center of the cog teeth.
•put some spacers and your cog on the freehub. put a flat edge against the end of the axle ("lock nut") and measure horizontally from the end of axle to the teeth with the cog pressed gently against the spacer stack behind it. adjust spacers until the cog lines up with the number you've generated.

this is basic, simple, obvious math. it makes more sense when you do it in person. no more eyeballing and guessing, waiting to notice chainring wear. set it up mathematically right the first time and forget about it.

*your chainline is determined by your frame, bottom bracket, cranks, and chainring. if you want to change your chainline, you might be able to do so by changing the spacing of your BB cups, using a different length spindle (on square tape cranks), placing the ring on a different orientation on the spider, flipping the chainring over to change the offset, putting spacers on the ring, etc. since there are so many different types of cranksets on the market, it would be pointless for me to list all possible permutations of this.


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## NordieBoy (Sep 26, 2004)

I still put a straight edge up against the chainring and see how close it is to the rear cog.
No maths and easy to get within a mm or so.


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## Onegear3619 (Jul 23, 2014)

Amazon.com: Motion Pro 08-0048 Chain Alignment Tool: Automotive


Buy Motion Pro 08-0048 Chain Alignment Tool: Tool Kits - Amazon.com ✓ FREE DELIVERY possible on eligible purchases



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It's for a Moto but should work or just get it close and ride. If the chain doesn't come off it's lined up.


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## jay91_ss (Apr 7, 2019)

Wrong thread 🙄


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