Radical new CRANK - your thoughts?

Discussion in 'Cycling Equipment' started by Bigbananabike, Oct 21, 2007.

  1. Bigbananabike

    Bigbananabike Member

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  2. BikingBrian

    BikingBrian New Member

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    Well, my French is a little rusty, but I gathered that basically it's a system to get through the dead spots faster/with less effort....so the same concept as ovalized chainrings, etc. This "dead spot" thing is beating a dead horse - it's been shown that pro cyclists produce power only in the phase where you are pushing, ie forward, and more importantly, DOWN. The study I read about found no sizable power application in the "pulling" phase, iow they use their quads almost exclusively, as very little power is produced by the hamstrings. SO....getting through the "dead spot" faster, or trying to produce more power in that phase of the pedal stroke appears to be meaningless. This product does nothing new, it just reinforces old myths.
     
  3. LeDomestique

    LeDomestique New Member

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    Mmm...this one seems to vary the length of the crank arm with each revolution as well. At the very least it seems a bit more elaborate than your traditional "Biopacing" cranks.
     
  4. dgregory57

    dgregory57 New Member

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    There is a link on the left that provides a link to an English page...

    I do see that it seems to combine an ovalized ring with a variable crank length... Seems like some added complexity that I would be a little cautious to adopt the technology due to potential reliability issues, and also issues of potential ergonomics.

    I would like to see some independent orthopedists' opinions on how it impacts the health of riders' joints.

    Of course, I am a casual rider, and would be unlikely to pay extra for it even if it was healthy and did improve efficiency. ;)
     
  5. Bigbananabike

    Bigbananabike Member

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    Ok, but Rotocranks(I think that's what they're called) that are independent of each other help to produce more power in the hamstrings which(reading riders write up) seems to help riders go faster.

    For many people the longest aspect of the cranks will be too long(moot point I guess) even for hill climbing.
    For spinning I can't see the use of a crank that long(at its longest) when cranks are flying around at over say 110rpm +
    They seem to be only useful hillclimbing.





     
  6. ScienceIsCool

    ScienceIsCool New Member

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    But the limit on power output isn't dependent on which muscle group is active (i.e., size of engine). The total power output is highly dependent on the respiratory system, VO2max, etc. In other words, how much fuel you can get to the engine. So adding another muscle group does nothing to change that.

    If it could change that, the body would adapt and make the quads bigger/more powerful to take advantage of the current crank designs. But the average pro cyclist shows that is not the case. Ergo sum, the current design is optimized to accomodate the full potential of the human design. I.e., there is no point making the engine bigger if you can't supply it with more fuel.

    John Swanson
    www.bikephysics.com
     
  7. Insaneclimber

    Insaneclimber New Member

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    The pedeling motion on the vids looks jerky, which i think would make the cranks a pain, I wouldent know untill i did a fast paced 5 hour ride to see what the effect on the body was, i have seen another design useing a pivoting crank arm that worked on the same principle of increasing the stroke length in the power phase. that was a flop.
     
  8. CAMPYBOB

    CAMPYBOB Well-Known Member

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  9. ScienceIsCool

    ScienceIsCool New Member

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    Okay. But then there has to be a rational explanation. The respiratory efficiency will remain unchanged (VO2max, respiration rate, blood flow, etc) between different crank types. The biomechanical efficiency will stay the same since the range of motion does not change (i.e., the same muscle groups perform the same amount of work at roughly the same joint angles).

    Another possibility is that for a given input force, the system is optimized for output torque/power. This seems to be the operating principal behind these cranks. And many, many others including the old Shimano Biopace. Looking at past designs, the efficiency gains have been very, very marginal (create some force diagrams and integrate to find total power output/efficiency).

    Without seeing some detailed torque versus crank angle diagrams, it's very difficult to believe the claims of an 11% gain. The design is not sufficiently different from past designs to account for such an increase in efficiency. It's also not clear *how* they measured this change in VO2 vs power output. The noise in their data (and systematic error) could account for the differences that they measured.

    Colour me skeptical...

    John Swanson
    www.bikephysics.com
     
  10. ScienceIsCool

    ScienceIsCool New Member

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    I forgot something. You also need to compare the results against normal cranks of different crank lengths. The max extension on these is something like 187 mm. How do the results compare to fixed length cranks of 180, 185, and 190 mm? It could be that the test subject(s) were fitted on the bike such that their optimal biomechanical efficiency is at ~185 mm.

    John Swanson
    www.bikephysics.com
     
  11. artemidorus

    artemidorus New Member

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    You believe this? No published literature or independent source is cited. Similar claims have been made and debunked before. When the protour starts using these in races, then I might consider believing it.
     
  12. 11ring

    11ring New Member

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    I think you are mistaken here, as the path of the pedals is circular and of standard radius (175mm, ill have to check), I believe as the crank arms get longer their centre of axis moves away from the bb such that the pedal path is circular and app 175mm diamater.
     
  13. 11ring

    11ring New Member

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  14. Oruboris

    Oruboris New Member

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    Does anyone else remember... I think they were called 'biopace' cranks, back in the 80's. Were somewhat oval, so you were moving more teeth on the downstroke and fewer at the top and bottom of the circle.

    Seemed to make sense at the time, but never really caught on.
     
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