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View Poll Results: Where - And which way round?

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  • Front - Right-Way-Round

    2 33.33%
  • Front - Back-To-Front

    1 16.67%
  • Back - Right-Way-Round

    2 33.33%
  • Back - Back-To-Front

    1 16.67%
Results 1 to 12 of 12
  1. #1
    Senior Member CaptCarrot's Avatar
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    Bottle Dynamo - Mounting Position

    OK, just wondering what you guys think on the mounting position of a bottle dynamo. Left/Right side is not an issue, but front/back and right-way-round/back-to-front, is less obvious to me and I was wondering what you guys think.

    The last bike I had with a bottle had it mounted back-to-front on the right side of the rear wheel.

    However, that had halogen lights. I am obviously getting LED lights, and am therefore planning to pass the power to the rear light through the front, as opposed running separate cabling from the bottle to each light, due to the way LED lights are designed.

    With that in mind, it would make more sense to place the bottle on the front. But if the better traction would be gained from the back then I would have to run a cable down and back again.
    Not as green as I might be cabbage looking!

  2. #2
    Senior Member Road Fan's Avatar
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    I think your choices are not obvious.

  3. #3
    Ding! Bandera's Avatar
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    Quote Originally Posted by Road Fan View Post
    I think your choices are not obvious.
    2nd that, I've fitted many dozens but don't ken.
    Pics?

    -Bandera
    '74 Raleigh International - '77 Trek TX900FG - '92 Vitus 979 - '10 Merckx EMX-3- '11 Soma Stanyan

  4. #4
    Senior Member Road Fan's Avatar
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    I see two ways to mount any bottle dyno: ahead of the fork or seatstay, or past the fork or seatstay. In the first case, the rotation of the tire tends to pull the dyno toward the tire, increasing the roller contact pressure. Some people think there is an inherent failure mode in this, that the dyno may fly loose of it's moorings and damage the wheel or frame. Second case is that the dyno is past the fork (in front of it, actually), so that the tire tends to push the dyno away from it, reducing roller contact pressure. It would seem safer, but there is the potential for less performance.

    How do these mounting strategies correspond to the choices you offer?

  5. #5
    Senior Member CaptCarrot's Avatar
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    My apologies if my options were not clear.

    Quote Originally Posted by Road Fan View Post
    I see two ways to mount any bottle dyno: ahead of the fork or seatstay, or past the fork or seatstay. In the first case, the rotation of the tire tends to pull the dyno toward the tire, increasing the roller contact pressure. Some people think there is an inherent failure mode in this, that the dyno may fly loose of it's moorings and damage the wheel or frame. Second case is that the dyno is past the fork (in front of it, actually), so that the tire tends to push the dyno away from it, reducing roller contact pressure. It would seem safer, but there is the potential for less performance.

    How do these mounting strategies correspond to the choices you offer?
    Precisely.

    There are actually 2 questions, to mount on the front or rear wheel, and to mount "right-way-round" or "back-to-front". There is also the question of left or right side mounting, however I have already answered that one for myslef.

    So to mount fore or aft?

    I have always mounted bottles on the rear wheel in the past, and run 2 sets of wires from them - 1 to the front and 1 to the rear. However, due to the way LED dynamo lights are designed, it is better to run the rear light from the second set of connectors on the back of the front light, this assures the front light gets it maximum power and is not dimmed by the rear lights. This is however, an unknown territory for me and it is unknown if the difference would be noticeable.

    If I mount on the rear, but try to work with LED lights as intended, I would have to run a wire down the bike twice. However, should there be a mis-hap and the dyno jam the wheel, I feel a rear wheel jam (skid) is safer than a front wheel jam (launch over handlebars).

    Now to the orientation.

    "Right-way-round" refers to mounting the dyno "after" the front fork or seat stay, so that the motion of the wheel would carry it away from the fork/stay in the event of bracket failure.

    Where-as "back-to-front" refers to mounting the dyno "before" the front fork or seat stay, in this configuration the dyno would likely be dragged into the fork/stay in the event of bracket failure.

    Whichever way the dyno is mounted, there is always a risk it could jam the wheel if it comes loose. However this is magnified by the proximity to the fork or seat stay if mounted "back to front".

    The benefit of running "back-to-front" is that the motion of the wheel, acting on the dyno and dyno-mount, has the effect of drawing the the dyno against the tyre and minimising slippage as the two "pinch" together. If run "right-way-round" the dyno is effectively being pushed away, and is therefore more likely to slip if the sidewall becomes contaminated with debris or possibly water.

    I hope this clears it up.
    Not as green as I might be cabbage looking!

  6. #6
    Senior Member
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    Then I'd say Front - Back-To-Front, but then again that's because my bicycle has a bracket for a dynamo. But the wording is still very clumsy.

  7. #7
    Senior Member CaptCarrot's Avatar
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    Quote Originally Posted by harshbarj View Post
    Then I'd say Front - Back-To-Front, but then again that's because my bicycle has a bracket for a dynamo. But the wording is still very clumsy.
    My apologies - how else should I word it?
    Not as green as I might be cabbage looking!

  8. #8
    Ding! Bandera's Avatar
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    Quote Originally Posted by CaptCarrot View Post
    If I mount on the rear, but try to work with LED lights as intended, I would have to run a wire down the bike twice. However, should there be a mis-hap and the dyno jam the wheel, I feel a rear wheel jam (skid) is safer than a front wheel jam (launch over handlebars).
    Planning a "high-side" on failure of a loose fitting vs. "Hey, what's wrong w/ my light?" is not worth a Poll.
    Running a bit of wiring vs. lying face-planted down on the street in the event of failure: lets see...can't make up my mind......
    A failure in dynamo mounting should result in a lack of light, not a "launch" or "skid".

    Try a new Poll:

    1) Dark
    B) Launch over bars
    iii) Unexpected rear lock-up

    -Bandera
    Last edited by Bandera; 09-05-13 at 08:11 AM.
    '74 Raleigh International - '77 Trek TX900FG - '92 Vitus 979 - '10 Merckx EMX-3- '11 Soma Stanyan

  9. #9
    Senior Member Road Fan's Avatar
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    and don't forget

    foah) unexplainable forks asploshun.

    sorry, that should have been "unasplainable"

  10. #10
    Senior Member CaptCarrot's Avatar
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    Quote Originally Posted by Road Fan View Post
    and don't forget

    foah) unexplainable forks asploshun.

    sorry, that should have been "unasplainable"
    Don't get it.

    Sorry.
    Not as green as I might be cabbage looking!

  11. #11
    Senior Member Road Fan's Avatar
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    My apologies, just an attempt at gratuitous silliness.

    As far as bottles go, I prefer to mount them so the tire pulls the roller in to improve contact. I try to mitigate the failure mode of a dyno coming loose by mounting them very solidly.

  12. #12
    coprolite fietsbob's Avatar
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    My Brompton had it on the right side , the mounting bracket was on a rack strut , the only steel strut ,
    the other 3 were aluminum.

    useless when the tire gets wet, so I use hub dynamos now.

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