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  1. #1
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    correct chain length?

    I'm doing the last touches on my Flux buildup, and this nagging question is postponing the buildup.

    I removed the top bolt of the shock and swung the shock out of the way. With the front rocker bolt hole and bottom shock mount at 6 1/2", the rear axle to center of BB measurement is 16 7/8". I cycled the suspension until the front bolt on the rockers and bottom shock mount was 5". Now the rear axle to center of BB measurement is 17 1/4". Shouldn't I be able to have the suspension completely uncompressed (6 1/2" shock length) and then go big / big and add two links? The compressed suspension only lengthens the effective chain stay by 3/8" of an inch, so the chain would not get too tight when the suspension is fully compressed.

    If I went big / big and added two links when the suspension is fully compressed, the chain would be a little too slack when uncompressed, and there would be a higher chance of the top derailleur pulley rolling on the largest cog when climbing in granniest of grannies. SEE HERE

    What do you think?

  2. #2
    Just another FOC'er
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    I like my chain with the least slack possible and always have it just long enough to have a little slack in the big-big at bottom out. I've never had a problem with this and it seems to minimize slap.

    If the derailleur pulley is hitting on the largest cog on the cassette tighten down the 'B tension' screw a little. Too little it'll hit, too much and the shifting will get a little less precise.

  3. #3
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    Quote Originally Posted by royta
    I'm doing the last touches on my Flux buildup, and this nagging question is postponing the buildup.

    I removed the top bolt of the shock and swung the shock out of the way. With the front rocker bolt hole and bottom shock mount at 6 1/2", the rear axle to center of BB measurement is 16 7/8". I cycled the suspension until the front bolt on the rockers and bottom shock mount was 5". Now the rear axle to center of BB measurement is 17 1/4". Shouldn't I be able to have the suspension completely uncompressed (6 1/2" shock length) and then go big / big and add two links? The compressed suspension only lengthens the effective chain stay by 3/8" of an inch, so the chain would not get too tight when the suspension is fully compressed.

    If I went big / big and added two links when the suspension is fully compressed, the chain would be a little too slack when uncompressed, and there would be a higher chance of the top derailleur pulley rolling on the largest cog when climbing in granniest of grannies. SEE HERE

    What do you think?
    If you go big-big with the suspension uncompressed and then add a link, you will have the slack you need should you ever find yourself in a situation where you are completely cross-chained and end up bottoming out...how often is that even likely to happen, anyway? Two links are more than you need to accomodate the chain line growth from the suspension compression. Some guys here set up their chain even tighter and are careful not to cross-chain, but that is an exception vs. the rule. From there, the rest of the adjustments are made at the rear derailleur--follow the set-up instructions to the letter and it should work fine, assuming that you are working with new parts and are not also trying to sort out battle damage on transfered bits.. One last idea--the Park Tool site has a good section on deraileur setup and adjustment---that helped me sort out a rear derailleur setup that my (former) LBS had completely goobered up.
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  4. #4
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    When I first started replacing chains and derailleurs on my first hardtail, I would set the chain length one link shorter than big / big. I never, ever cross chain, and I felt it kept the derailleur spring tighter which would speed the shifting. I've been playing it a little safer lately.

    I always thought rear derailleur set up was easy. It's the front derailleur that is the trouble item. Experimenting with height, making sure it's perfectly parallel with the rings. A bunch of trouble.

  5. #5
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    Quote Originally Posted by royta
    When I first started replacing chains and derailleurs on my first hardtail, I would set the chain length one link shorter than big / big. I never, ever cross chain, and I felt it kept the derailleur spring tighter which would speed the shifting. I've been playing it a little safer lately.

    I always thought rear derailleur set up was easy. It's the front derailleur that is the trouble item. Experimenting with height, making sure it's perfectly parallel with the rings. A bunch of trouble.
    Yeah, well my plan is to never go big-big too, but every once in a while I'll shift to the big rear thinking I'm in the middle front... Oops

  6. #6
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    length

    On an XC bike I have always used the Shimano method even on a SRAM set up.
    When in high gear, the jockey pulley centerline is vertical. It worked in '87 and just last week I was updating my Flux parts and it works today. I can still go big big and the rear mech will work plenty of reasonable choices down the cog set.

    DT

  7. #7
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    Quote Originally Posted by turnerbikes
    On an XC bike I have always used the Shimano method even on a SRAM set up.
    When in high gear, the jockey pulley centerline is vertical. It worked in '87 and just last week I was updating my Flux parts and it works today. I can still go big big and the rear mech will work plenty of reasonable choices down the cog set.

    DT
    It just so happens that the big big and add two links automatically did that. I believe the pulleys are also vertical when in granny of all granny low too. Thanks Dave.

  8. #8
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    Quote Originally Posted by turnerbikes
    On an XC bike I have always used the Shimano method even on a SRAM set up.
    When in high gear, the jockey pulley centerline is vertical. It worked in '87 and just last week I was updating my Flux parts and it works today. I can still go big big and the rear mech will work plenty of reasonable choices down the cog set.

    DT

    Just to make sure I have this right, you are saying big ring and highest (smallest cog either 11t ot 12t) in the back?

  9. #9
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    Quote Originally Posted by AzSpeedfreek
    Just to make sure I have this right, you are saying big ring and highest (smallest cog either 11t ot 12t) in the back?
    That is incorrect. Big-big means the large ring in front and the largest, innermost cog in bag.

    This combination requires the longest chain, which is why we were describing the correct chain length as "big-big plus something..."

    Riding in that combination (big-big) or in the opposite combination (small-small) is called "cross-chaining" and is not recommended because the chain line angle is severe, and in big-big the rear derailleur is stretched pretty tight. It's hard on the parts (wear out faster, more likely to break if you are really hammering).
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  10. #10
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    Dead Man Walking - I think he's referring to DT's suggestion on setting up chain length.

  11. #11
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    Quote Originally Posted by royta
    Dead Man Walking - I think he's referring to DT's suggestion on setting up chain length.
    Hmmm...you are right. I re-read DT's post. Ooops...

    (Gotta finish that first cup of coffee before jumping on the boards)
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  12. #12
    I think I need to Upgrade
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    Quote Originally Posted by Dad Man Walking
    Hmmm...you are right. I re-read DT's post. Ooops...

    (Gotta finish that first cup of coffee before jumping on the boards)

    That or stop having Irish Coffee in the morning .

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