Chain lines are a changin-
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  1. #1
    mtbr member
    Reputation: keefe's Avatar
    Join Date
    Jan 2004

    Chain lines are a changin

    Is it just me? I have a new XCL that I have only ridden once here in Jersey due to the weather and it shifted perfect I might add. But...

    Back in 99 I had a Trek hard tail and the straightest chain line was in the middle chain ring and 2nd cog. Then in 02 I got a Titus Switch Blade and the straightest chain line was 2nd chain ring and 4th cog. My new XCL's straight chain line looks like it's middle chain ring and 6th cog.

    Again in the stand and the one time I rode it the shifts were perfect. I spend most of my time in the middle chainring seems like on the 2nd or 3rd cog and looks like I'll never be going in a straight line again.

    I don't think this is a Chumba issue, it's really an industry issue with triple chain ring long travel bikes.

  2. #2
    mtbr member
    Reputation: Mar-deeb's Avatar
    Join Date
    May 2007
    I had the same observation; I too am used to Middle Ring - Middle Cog chain lines so I spent a lot of time mulling over the line on my new XCL as well, some clarification from Chumba whould be nice.

  3. #3

    Join Date
    Apr 2007
    With a the larger 9 speed cog set you have a odd number and it should land you chain on the 5th gear or close. If it is on your 6th it is no big deal it will only make it a little more efficient on the gears in that direction.
    There are ways to tighten your chain line but it will work fine if it is close.
    Many hubs fluctuate and BB's also fluctuate in spacing. This make it hard to get it spot on.
    Sometimes its luck. I have seen cranks that are the same brand and same model, year that spaced different by almost 2mm.

  4. #4
    Compulsive Bike Builder
    Reputation: DirtDad's Avatar
    Join Date
    May 2002

    Integrated cranks...

    I don't know Chumba's numbers, but on a related note...

    One of the bummers of integrated cranks is - for the most part - they don't have adjustable chainlines. The spindle width is fixed, whereas with a separate BB you could buy a BB with a longer/shorter spindle. So far, no one offers integrated cranks with different spindle lengths - not that I have seen anyway. They offer different BB shell widths, but that is different.

    It does not count to rearrange the bb spacers because that just makes the crank off center, but I have seen it done. On Chumbas, you don't use any spacers anyway because they are 73 mm + e type, so you don't even have that option. Raceface's system allows for 1 or 2 mm chainline adjustment, that is about the best I have seen.
    Disclaimer: ComCycle USA

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