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  1. #1
    Transition Blindside v5
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    New question here. Q?: chainline measurement (front vs rear) - how close is sufficient?

    Hi all,

    (I'm a SS newbie, and have read the FAQ & Sheldon, and did a search on "chainline" (back to late-'09). Not wanting to hijack somebody else's "sorta-close" posts with my question, I'm starting a new post.)

    So, this used SS-converted "budget" bike (for DJ) that I just picked up has a 73mm/shell x 113mm/spindle BB for 48.5mm chainline (on paper) up front, and I also measured it with a ruler myself (per Sheldon) to see that it's just about that (or maybe 47.5mm-ish). It has a 175mm-arm Truvativ triple-ring crankset (which I'd like to replace), and a 32T ring mounted on "inside" of the spider.

    On the rear, I also measured the chainline with a ruler and did the math (per Sheldon), and it's about 45mm~45.5mm ( = 135mm/2 - 22mm-ish). Rear wheel has Sette (Pricepoint) SS Conversion Kit, with its 18mm spacer inboard, then 18T cog, then 16mm spacer outboard (w/ regular QR-135mm vertical dropouts).

    So, I got a 2mm~3.5mm difference. How close do I have to get it all aligned? Exactly, or what's "sufficient" (eg. "within 2mm", etc.)?

    I suppose I can either use spacers to bring in the 32T chairing up front, or... On the rear, since Sette kit only has 2 big spacers (not many choices), should I replace it with Performance kit (which has many thin spacers for more cog-location options)?

    Thanks for your feedback in advance,
    - PiroChu
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  2. #2
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    I don't bother measuring. I'll just put the chain on, and then eye it from the rear. If the chain is straight, it's good enough. Using that method I haven't had any dropped chain (and I used a multispeed chainring for a long while) or any skips, and my chain life is great.

  3. #3
    meatier showers
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    Quote Originally Posted by bad mechanic
    I don't bother measuring. I'll just put the chain on, and then eye it from the rear. If the chain is straight, it's good enough. Using that method I haven't had any dropped chain (and I used a multispeed chainring for a long while) or any skips, and my chain life is great.
    I use the eyeball method with great success, too.

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  4. #4
    PeT
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    When setting up a new singlespeed I've usually got the chainline pretty close based on the specs of the parts and it looks pretty good by eye. But the test I always run before taking it out on the trail is to set it up with the chain sort of loose -- a noticeable sag in the middle so that you could probably derail the chain if you used your hand to push the chain to the side as you pedal the cranks. Then I spin the cranks by hand as fast as I possibly can (in both directions, so it's best done in a repair stand). If the chain stays on, it's good enough. I snug up the chain and go riding. I've yet to have a chain come off on the trail when using that method of testing. I came to using it some years ago through diagnosing the issues with a SS that had lost the chain bouncing through some potholes with a subsequent over-the-bars event as I stood to sprint through an intersection -- both painful and embarrassing as I dumped it in front of a crowd...
    "The plural of anecdote is not data." -- Attributed to various people in a variety of forms, but always worth remembering...

  5. #5
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    For the cost of the spacer kit, I'd upgrade. I've used the Surly kit quite a few times with great success.

  6. #6
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    Get the little spacers, or go to a bike shop and get those plastic ones from some old cassette.

  7. #7
    Transition Blindside v5
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    New question here. single-ring (vs triple) DH/FR crankset ?

    OK, thanks, guys, I'll just consider my figures (above) to be "sufficient", then.

    By the way, in respect to singlespeed setup, what are there differences between single-ring DH/FR crankset vs its multi-ring counterpart? (eg. Shimano Saint FC-810-1 vs FC-810-2; Raceface Atlas AM vs Atlas FR; Truvativ Stylo 1.1 vs 2.2; etc., etc.) Are they just "packaged differently" (same spider/arms with just a different ring configuration), or is the spider actually designed differently (eg. can only mount one ring, etc)?

    Just trying to decide whether to get a single-ring crankset, or get a normal triple set and utilize its middle-ring position.

    Thanks again,
    - PiroChu
    Last edited by PiroChu; 10-27-2010 at 07:14 PM.
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  8. #8
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    I usually measure mine as you have done and try to get it within 1-2mm. Any more is too much in my book but I come from a trials background where there is much greater force on the chain (think 18:15 ratio with large static loads and 370mm chain stays).

    In regards singlespeed cranksets, often they start off life the same in the factory but the SS version doesn't have the granny ring bolts holes drilled or tapped and they come with a bash guard, not a large chain ring.

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