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  1. #1
    What??? Only 2 wheels? jimmuller's Avatar
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    Eccentric high or low?

    I have started re-assembling the '82 Peugeot TH8 for which I've been gathering parts through the winter. One seeming option is the vertical position of the captain's BB eccentric. It could be mounted with the BB centerline above or below the shell's centerline. The effect is to place the BB higher or lower, exactly how much depending on the longitudinal position.

    The '82 and '83 catalogs online seem to have placed the BB high. Two of the bikes pictures in PeugeotTandem.com seem that way too, but another seems to have placed the BB low.

    I'm just wondering what the effect is, other than the obvious of placing the captain higher or lower. Lower means more likelihood of ground strike by a pedal.

    I'm about 5'9", 162 lbs, the stoker is about 5'2" and maybe 110 lbs.
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    jimmuller

  2. #2
    pan y agua merlinextraligh's Avatar
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    I put ours higher for the pedal strike reason, which actually matters when you race it. Otherwise I don't think it matters a lot. Lower would give you a bit lower center of gravity, but with the pedal strike trade off.
    You could fall off a cliff and die.
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  3. #3
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    Putting it higher allows the stokers bars to be raised higher if that matters.
    It also changes the captains saddle height relative to the bars.

  4. #4
    Senior Member zonatandem's Avatar
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    The purpose of the eccentric is to keep the crossover chain snug; whether high/low or level front/back is up to you.

  5. #5
    PMK
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    FWIW, all of our tandems, both dirt and road run the eccentric with the BB up. As mentioned in post #2 & #3 are why, offroad for strikes, all around on account of stumpy captain legs...and while I would like to be a pirate, oh wait those are peg legs.

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  6. #6
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    If you did the below centerline , your downward force could loosen your chain if it moves . Hi setting wood make it tighter if it moves. Did not see it mentioned.

  7. #7
    car guy, recovering aixaix's Avatar
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    If you did the below centerline , your downward force could loosen your chain if it moves .
    Wouldn't precession (the reason left pedals have left-hand threads) make it tend to rotate the opposite way? Not that it really matters: if the pinch bolts are tight, it shouldn't move at all.
    Michael Shiffer
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  8. #8
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    Interesting point but I would consider downward force as the ruling factor here & the pedals are 2 seperate rotational forces . I do understand what your saying. There are about 7 tandems in our group now . Only one is below center & thats the one with the droopy chain.

    ? Coincidence ?

  9. #9
    Senior Member zonatandem's Avatar
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    Yes, coincidence.

  10. #10
    tcs
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    Over the last 27 years riding my Santana, I've found the timing chain loosens quicker if the BB is low in the eccentric.
    "When man first set woman on two wheels with a pair of pedals, did he know, I wonder, that he had rent the veil of the harem in twain? A woman on a bicycle has all the world before her where to choose; she can go where she will, no man hindering." The Typewriter Girl, 1899.

    "Every so often a bird gets up and flies some place it's drawn to. I don't suppose it could tell you why, but it does it anyway." Ian Hibell, 1934-2008

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