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  1. #1
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    42 mm chainline? What's the point?

    I've been in the market to get a new crankset. I have been using the Sugino RD crankset. This set delivers a 45 mm chainline, which works fine with the 3/32 8-speed chain (and this is true even of the Sugino Messengers -- this is just an RD set-up with a higher-quality chainring). But I have been considering getting a crankset that will give me that sought-after 42mm chainline. I just have not been able to find any good reasons to do this. So I am considering just getting some shiny new RDs with good-looking Messenger rings.

    I have encountered two sets of opinions on this shift in chainline lenght on fixies: Some say "Wider chainline is fine. It doesn't really make a difference to the performance of the bike. Just keep the right kind of chain on there to keep you from eating a dirt sandwich and you should be fine"; one of my lbs mechanics (who has historically given good advice) says this, see what queerpunk says here So when did RD2's switch to 45mm chainline?
    and I know that Eric Sovern thinks this as well (he is one of the head guys at Surly). In short, a good 3/32 chain is all you need to use this kind of crank set-up. And, when you use this chain, you get more chainring options to boot.

    The other side thinks that going this far beyond the traditional 42mm is just stupid. Some say that there may be greater wear on the components due to this; others say that this set-up is just not as efficient (due to the deviation from rear cog to chainring). See, e.g., what Landgolier says here Sugino RD2 chainline frustrations
    and the discussion with E. Sovern about using Sugino RDs on the Steamroller complete here:
    Is a 46mm chainline a problem.

    There are some angry people in this last thread. The question is: why?

    So, let the mud-slinging begin. Is the 42mm chainline just a rule of thumb to be violated with impunity? Or is it the golden rule to be adhered to with fear and trembling? (I like use big words)

  2. #2
    matters cryptozoological
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    hey sinn, without reading too much into what you're trying to say, it doesn't matter what chain line you have, so long as it's reasonably straight. 42mm happens to be what most track hubs give, so in the interests of achieving a straight chain line, the chainring should also be as close to that 42--mostly for reasons of safety, and only slightly for reasons of pedaling efficiency and mechanical wear.

    so, if your rear hub gives you a chain line of 45mm, just make sure your chainring gives something reasonably close to 45 as well. 42 isn't a golden rule, it's just what's most often found.

  3. #3
    hello roadfix's Avatar
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    I'm not anal about cogs and rings having perfect chain lines.

  4. #4
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    Quote Originally Posted by jlin View Post
    hey sinn, without reading too much into what you're trying to say, it doesn't matter what chain line you have, so long as it's reasonably straight. 42mm happens to be what most track hubs give, so in the interests of achieving a straight chain line, the chainring should also be as close to that 42--mostly for reasons of safety, and only slightly for reasons of pedaling efficiency and mechanical wear.

    so, if your rear hub gives you a chain line of 45mm, just make sure your chainring gives something reasonably close to 45 as well. 42 isn't a golden rule, it's just what's most often found.
    I agree with what you say. That makes sense. But I think that you may have misunderstood the question. Let me put it this way: Given that most rear hubs "require" a 42mm chainline, what is the problem with letting the chainline deviate 3 mm?

  5. #5
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    If the chainline isn't straight, you loose some efficiency. You can also run the risk of the chain coming off. Whether this is a big issue with just 3mm, I don't know. But you might want to try and get it so that it is at most 1mm apart. Can you change the spacers on your rear hub?

  6. #6
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    Quote Originally Posted by pax139 View Post
    If the chainline isn't straight, you loose some efficiency. You can also run the risk of the chain coming off. Whether this is a big issue with just 3mm, I don't know. But you might want to try and get it so that it is at most 1mm apart. Can you change the spacers on your rear hub?
    No, I don't think I can. The Surly hub makes a tight fit with the Surly cog. But, I've emailed Eric Sovern (the guy from Surly) and I've asked my mechanic, and I've ridden it for a long time without trouble with an 8 speed chain, and all of these tell me that there is no porblem with this set up, and that, in fact, there is no reason to get a crank set that can supply anything closer than 45 mm.

    Do you have experience with this? Was the loss in efficiency even noticeable?

  7. #7
    brap brap
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    So has anyone gotten any closer to finding cheap cranks that get closer to 42mm then those sugino rd's?

  8. #8
    yo yo yo yo yo
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    i've always eyeballed chainlines with fine results. if it looks like it's far enough off to cause a problem - that is, fall off the chainring/cog - fix it. otherwise i wouldn't bother.
    Quote Originally Posted by tx_what_it_do View Post
    machined are for brakes. non-machined are more for brakeless.

  9. #9
    big ring MIN's Avatar
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    Track hubs with nominal 42mm chainlines measure out to 44mm-45mm depending on the cog you use.

  10. #10
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    A 42mm chainline provides the most Zen.
    "Anyone who has never made a mistake has never tried anything new"
    - Albert Einstein

  11. #11
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    Quote Originally Posted by speeed View Post
    So has anyone gotten any closer to finding cheap cranks that get closer to 42mm then those sugino rd's?
    yes, the alien/andel/kazane/hellyer cranks. i got the silver alien cranks for 89 + shipping.
    http://www.alienbikes.com/gear.html
    looks like they're out of stock now though.

  12. #12
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    Wow. I thought that this thread was dead and gone.

  13. #13
    Villainous huerro's Avatar
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    Quote Originally Posted by speeed View Post
    So has anyone gotten any closer to finding cheap cranks that get closer to 42mm then those sugino rd's?
    Ebay is full of good cheap old cranks. My local CL has plenty as well. Find one, get the right bb spindle and ride in 42mm bliss.

  14. #14
    Senior Member mihlbach's Avatar
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    http://www.londonfixiebike.co.uk/shop.html

    Here is the best solution to the 45 mm chainline dillemma of the RD crankset. With zero dish, a converted Shimano M756 hub yields a 46mm chainline and gives you an unstrippable hub/cog interface.

  15. #15
    brap brap
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    Quote Originally Posted by Sinn View Post
    Wow. I thought that this thread was dead and gone.
    sorry for using the search feature, next time i'll start a whole new thread so everyone can give me great advice


    thanks. i think i'm going with andel cranks

  16. #16
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    Quote Originally Posted by speeed View Post
    sorry for using the search feature, next time i'll start a whole new thread so everyone can give me great advice


    thanks. i think i'm going with andel cranks
    No no. I meant that in a positive way.

  17. #17
    King of the Hipsters
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    About three years ago I rode with an RD crank and I liked it.

    I write this from memory and I might have it all wrong, so check it out for yourself.

    Anyway, it seems to me the RD has an inner ring position and an outer ring position for two chain rings.

    I think I put my chain ring on the inner position and it gave me, if not a perfect chain line, a silent chain.

    I might have that all wrong, but I do remember having a silent chain with the RD.

  18. #18
    Does Not Exist
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    A typical road double crankset will give 41mm on the inner position.

  19. #19
    cab horn
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    Sigh.

    A narrower chainline allows a narrower q-factor.

    End of ****ing thread.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

  20. #20
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    Quote Originally Posted by MIN View Post
    Track hubs with nominal 42mm chainlines measure out to 44mm-45mm depending on the cog you use.
    Do you recommend any particular cog to get a 44-45mm chainline out of a Formula ~42mm nominal hub? I'd like to run Sugino RD's or Messenger's and I'd like to get it as accurate as possible.

  21. #21
    big ring MIN's Avatar
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    I measured 44mm with a EAI cog on a Formula hub. Good luck.

  22. #22
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    Thanks for the info MIN.

  23. #23
    King of the Hipsters
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    Quote Originally Posted by efficiency
    A typical road double crankset will give 41mm on the inner position.
    If so (and I don't doubt efficiency), this would explain why I had a quieter chain with the chainring mounted on the inner position of my RD crankset.

    42 - 41 = 1

    45 - 42 = 3

  24. #24
    Kanye West
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    what about 39 mm? is it worse to be on the inside

  25. #25
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    with 39mm it's unlikely to clear the chainstays, but if it does, no, it's the same as 45mm

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