Biopace Timing

Discussion in 'Cycling Equipment' started by RIPPERTON, Apr 24, 2007.

  1. RIPPERTON

    RIPPERTON New Member

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    My neighbor and I both have Shimano Biopace gear on our roadies but recently noticed the high spots on the chainrings were timed to engage the chain when the pedal was at 12 o'clock slowing the crank down during the dead spot which is the opposite of what you want. We decided some retiming was in order so he retarded both his chainrings 2 bolt holes, moving the high spot round to 4 o'clock and I advanced mine 1 bolt hole giving a 3 o'clock high spot. Both bikes are now much better to ride. We are new to Biopace and would like some history on this. Danny Sydney
     
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  2. serenaslu

    serenaslu New Member

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    Here is a pretty concise explanation of the theory of Biopace versus traditional elliptical design:

    http://www.sheldonbrown.com/biopace.html
     
  3. RIPPERTON

    RIPPERTON New Member

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    serenalsu that link doesnt work in my firefox thing.
     
  4. supergrill

    supergrill New Member

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    Hmm. Works fine in Firefox for me. :confused:
     
  5. artemidorus

    artemidorus New Member

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    They were correctly orientated before you touched them. I'd restore their original orientation, or go to round rings.
     
  6. RIPPERTON

    RIPPERTON New Member

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    Thats maybe where Shimano went wrong. The high spots should engage the chain when the leg has the most leverage on the crank ie 3 or 4 o'clock. And the low spots should spin the crank faster throught he dead spot ie 12 o'clock. There was a small pin sticking out of the large chainring that used to hide behind the crank arm and stop the chain from falling down and jamming so Shimano did intend the rings to be installed in that position but when you think about how and why Biopace is supposed to work, they were installing them the wrong way.
    [​IMG]
     
  7. ebow3d

    ebow3d New Member

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    Actually, that is exactly what Shimano did right, as apposed to all the other eliptical chainrings. I use a Biopace on a fixed gear bike that I've recently built up, and I can feel a positive difference, although it is not such a big improvement over a round chainring.
    This is a quote from Sheldon Brown's site: "The theory is that during the power stroke, when the cranks are more or less horizontal, you are using the power of your legs to accelerate your feet, which get going quite fast in the lower gear provided for that part of the stroke. The momentum of your feet then carries the pedals through the "dead spot" when the cranks are near vertical. Since the rider doesn't push as hard during the power phase of the stroke, and motion is slower when the leg is changing direction, the Biopace design is gentler on the knees than even round chainwheels."
     
  8. RIPPERTON

    RIPPERTON New Member

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    Ok so Biopace was intended as a passive aid to reduce strain on knees. I was assuming it was intended as a performance enhancer . The way I have it timed now the crank speeds up during the dead zone, spending less time there and more time in the power zone. I see Biopace as a 54 tooth cog with dips in it rather than a 52 tooth cog with bumps. Either way its better to ride.
     
  9. LOMAX

    LOMAX New Member

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    Shimano got the oval idea right but totally stuffed up on the orientation.
    Thats why Biopace was such a failure for Shimano.
    If you do some research on the net for Q rings & O Symetric you will find
    that these companies use opposite orientation to biopace and some of the
    current track elites are using these rings and winning world championships.
    I use biopace rings and use a similar orientation to q rings with good results.
    I have retarded my biopace rings 2 bolt holes.
    Well done Ripperton you have said what ive been wanting to say for a
    long time . I have been reluctant to make a mention of this because there are
    so many EXPERTS out there who would like to shoot this science down.
    Regards Andrew
     
  10. Slugster438

    Slugster438 New Member

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    Well, , , -it's the opposite of what you want. There's at least a couple different goals here, and you can't attain both at the same time.

    On an upright bike and with the pedals vertical--if you put the high spots horizontal, then the rider can move through the dead spots faster.

    On an upright bike and with the pedals vertical--if you put the high spots at roughly the one/seven o'clock positions, then you're shifting the torque load off the upper part of the pedal stroke, and pushing it into the lower part. The reason you'd do this is if you got knee pain early in the pedal stroke, but not in the lower-half of the pedal stroke (like me).

    You're kinda limited with a typical chainring's 72-degree increments however. Q-rings are the best right now for playing these games, even though they don't have the same shape as the BioPace did.
    --------
    I put up a page here showing the different shapes of some non-round chainrings compared, with their long axis oriented the same way and resized to the same maximum diameter. This diagram doesn't show them oriented as they are properly installed however; I meant to add another diagram showing that but haven't gotten around to it yet.

    ...And I only traced the best photos I could find online, and the shape depends on what size chainring you choose to use as an example (the smaller ones were usually "less-round" than the larger rings of the same brand). Additionally, there were at least two "official" BioPace versions (I and II, the second was milder than the first) and at least one more than that: someone from online with a small collection of BioPace rings claims there's at least three different shapes for a given size, and possibly four.
    ~
     
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