1. ## CHAINLINE math

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.

2. ## chainline for dummies.....

3. 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.

The Perfect Chainline

4. i think this thread should be stickied.

5. Wow, the SKEWER METHOD is a thing of beauty.

6. 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

7. ## +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 and +1 for making this a sticky. I read both, but used the ruler/math version.

8. 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.

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

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

11. Originally Posted by iridetitus
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.

12. 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.

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

14. Originally Posted by fishcreek
no. balls matters. or a ball, whatever is left.
+ 1

15. ## the post I'm waiting for:

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?

16. what kind of cranks?

17. 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

18. oxymoron

10speed/singlespeed?

no?

19. Originally Posted by Tone No Balone
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.

20. Originally Posted by 10speedbiopacefreewheel
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.

OK......

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

it's cool....

carry on....

in the SS forum.....

21. Originally Posted by Tone No Balone
OK......

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

it's cool....

carry on....

in the SS forum.....

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.

22. Originally Posted by 10speedbiopacefreewheel
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?

23. Originally Posted by Tone No Balone
but are any 29er's?
no. I tasted the kool aid and spit it out.

24. 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.

25. 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.

26. Originally Posted by TruTone
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.

27. Originally Posted by fishcreek
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.

28. Used Pursuiter's method. Perfect!

Thanks

29. post

30. ## 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.

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

32. 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?

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

34. 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......

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

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

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

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

39. 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

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

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

42. 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

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

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

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

46. 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.

47. What is a rear cassette?

48. Originally Posted by NordieBoy
What is a rear cassette?
LOL... The entire set of rear cogs is sometimes called a cassette.

49. Somethin that's not on a single speed LOL

50. 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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