Results 1 to 44 of 44

Thread: CHAINLINE math

  1. #1
    PSYCHOLUST
    Reputation: scyule's Avatar
    Join Date
    Nov 2009
    Posts
    482

    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. #2
    singletrack bound
    Reputation: Tone No Balone's Avatar
    Join Date
    Dec 2004
    Posts
    2,498

    chainline for dummies.....

    Sorrel Seeker !!

  3. #3
    one chain loop
    Reputation: fishcreek's Avatar
    Join Date
    Apr 2007
    Posts
    2,346
    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
    everything sucks but my vacuum cleaner.

  4. #4
    one chain loop
    Reputation: fishcreek's Avatar
    Join Date
    Apr 2007
    Posts
    2,346

    Good job!

    i think this thread should be stickied.
    everything sucks but my vacuum cleaner.

  5. #5
    PSYCHOLUST
    Reputation: scyule's Avatar
    Join Date
    Nov 2009
    Posts
    482
    Wow, the SKEWER METHOD is a thing of beauty.

  6. #6
    mtbr member
    Reputation: Cygnus's Avatar
    Join Date
    Jan 2004
    Posts
    477
    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. #7
    mtbr member
    Reputation:
    Join Date
    Jul 2010
    Posts
    86

    +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. #8
    mtbr member
    Reputation:
    Join Date
    Jul 2010
    Posts
    86
    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. #9
    mtbr member
    Reputation:
    Join Date
    Sep 2004
    Posts
    644
    so, wait.....chain line matters?
    ride fast...take chances...

  10. #10
    one chain loop
    Reputation: fishcreek's Avatar
    Join Date
    Apr 2007
    Posts
    2,346
    no. balls matters. or a ball, whatever is left.
    everything sucks but my vacuum cleaner.

  11. #11
    mtbr member
    Reputation: Cygnus's Avatar
    Join Date
    Jan 2004
    Posts
    477
    Quote Originally Posted by iridetitus View Post
    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. #12
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    35
    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. #13
    mtbr member
    Reputation:
    Join Date
    Mar 2004
    Posts
    223
    I like it. Thanks for making it sticky and even if it has been done, who cares? Good info is good info.

  14. #14
    mtbr member
    Reputation: ancient rascal's Avatar
    Join Date
    Mar 2010
    Posts
    3,614
    Quote Originally Posted by fishcreek View Post
    no. balls matters. or a ball, whatever is left.
    + 1 CHAINLINE math-0928110917a.jpg
    Still searching for my red headed hairdresser Tiffany. "Economic Mother Nature" ... Knocks at door! -AR

  15. #15
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    335

    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?
    no chain no gain.

  16. #16
    one chain loop
    Reputation: fishcreek's Avatar
    Join Date
    Apr 2007
    Posts
    2,346
    what kind of cranks?
    everything sucks but my vacuum cleaner.

  17. #17
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    335
    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
    no chain no gain.

  18. #18
    singletrack bound
    Reputation: Tone No Balone's Avatar
    Join Date
    Dec 2004
    Posts
    2,498
    oxymoron

    10speed/singlespeed?

    no?

    Sorrel Seeker !!

  19. #19
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    335
    Quote Originally Posted by Tone No Balone View Post
    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.
    no chain no gain.

  20. #20
    singletrack bound
    Reputation: Tone No Balone's Avatar
    Join Date
    Dec 2004
    Posts
    2,498
    Quote Originally Posted by 10speedbiopacefreewheel View Post
    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.....

    Sorrel Seeker !!

  21. #21
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    335
    Quote Originally Posted by Tone No Balone View Post
    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.
    no chain no gain.

  22. #22
    singletrack bound
    Reputation: Tone No Balone's Avatar
    Join Date
    Dec 2004
    Posts
    2,498
    Quote Originally Posted by 10speedbiopacefreewheel View Post
    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?
    Sorrel Seeker !!

  23. #23
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    335
    Quote Originally Posted by Tone No Balone View Post
    but are any 29er's?
    no. I tasted the kool aid and spit it out.
    no chain no gain.

  24. #24
    Frt Range, CO
    Reputation: pursuiter's Avatar
    Join Date
    May 2008
    Posts
    2,570
    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. #25
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    85
    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. #26
    one chain loop
    Reputation: fishcreek's Avatar
    Join Date
    Apr 2007
    Posts
    2,346
    Quote Originally Posted by TruTone View Post
    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.
    everything sucks but my vacuum cleaner.

  27. #27
    mtbr member
    Reputation:
    Join Date
    Jun 2011
    Posts
    85
    Quote Originally Posted by fishcreek View Post
    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. #28
    mtbr member
    Reputation:
    Join Date
    Nov 2011
    Posts
    243
    Used Pursuiter's method. Perfect!

    Thanks

  29. #29
    mtbr member
    Reputation:
    Join Date
    Mar 2012
    Posts
    6
    post

  30. #30
    mtbr member
    Reputation:
    Join Date
    Aug 2005
    Posts
    111

    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. #31
    mtbr member
    Reputation:
    Join Date
    Dec 2011
    Posts
    12
    I see a chain guide in the back. Does everyone use them?

  32. #32
    mtbr member
    Reputation:
    Join Date
    Oct 2010
    Posts
    329
    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?
    Something wrong with your bike? Blame it on super human strength and sleep well at night knowing you are more than a man.

  33. #33
    mtbr member
    Reputation: rob1035's Avatar
    Join Date
    Apr 2007
    Posts
    912
    I prefer the "float" method, since Im not so hot at math...

  34. #34
    mtbr member
    Reputation:
    Join Date
    Oct 2009
    Posts
    262
    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. #35
    mtbr member
    Reputation: pentlandexile's Avatar
    Join Date
    Jan 2013
    Posts
    44
    Redid my SS with new crankset and chain today using this method.... Perfect. Thanks for the post.

  36. #36
    mtbr member
    Reputation:
    Join Date
    Mar 2013
    Posts
    22
    wow, sweet advice, that made it so simple to get things right, thanks!!!!

  37. #37
    mtbr member
    Reputation:
    Join Date
    Mar 2009
    Posts
    24
    Thanks for posting this, just did this method when setting up my sawyer with a new crankset and it worked perfectly!

  38. #38
    mtbr member
    Reputation:
    Join Date
    Jun 2013
    Posts
    14
    Tried the method last night to realise my eyeballed setup was 5mm off. My Lynskey is dead on now thanks to this post !

  39. #39
    mtbr member
    Reputation: danorano's Avatar
    Join Date
    Nov 2012
    Posts
    64
    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. #40
    mtbr member
    Reputation:
    Join Date
    Jun 2014
    Posts
    5
    duct tape laser pen atop drive sprocket…swap spacers until cog lights up

  41. #41
    Armature speller
    Reputation:
    Join Date
    Sep 2004
    Posts
    1,767
    Straight edge against side of chain ring is the easiest and doesn't hurt your head with numbers.

  42. #42
    mtbr member
    Reputation:
    Join Date
    Oct 2015
    Posts
    10
    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. #43
    mtbr member
    Reputation:
    Join Date
    Apr 2014
    Posts
    377
    Motion-Pro chain alignment tool for motorcycles. Not sure why the idea never caught on in the pedal world. Too simple I guess...
    Specialized Stumpjumper HT

  44. #44
    Armature speller
    Reputation:
    Join Date
    Sep 2004
    Posts
    1,767
    Tried my motorbike chain alignment tool on the mtb.
    Now I use the straight edge on the motorbike as well.

Similar Threads

  1. SS math
    By scyule in forum Singlespeed
    Replies: 4
    Last Post: 11-20-2009, 02:37 PM
  2. Who can do the math...
    By Jowan in forum Cannondale
    Replies: 5
    Last Post: 04-22-2009, 08:07 AM
  3. Some one double check my chainline math
    By jager7 in forum Singlespeed
    Replies: 2
    Last Post: 11-11-2008, 05:06 PM
  4. a bike/math question...attn. math gurus!!
    By georgejetson in forum Alaska
    Replies: 7
    Last Post: 04-02-2008, 08:23 PM
  5. H Bar Math
    By Stroganof in forum 29er Bikes
    Replies: 9
    Last Post: 02-05-2007, 12:55 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •