The problem with that theory is that the pedal isn't indexed to a round chainring in any particular way. You can put a 90 degree (or any other, it makes no functional mechanical difference) bend in the crankarm, a curve or a double loop-de-loop and from a mechanical standpoint nothing really changes except you've simply moved the 'dead spot' relative to the chainring and weakened the arm for a given amount of material used.
Kurt Sperry Bellingham WA
On 6/30/06, The Maaslands <TheMaaslands@comcast.net> wrote:
>
> I remember reading about the PMP 90° cranks that the bend was claimed
> to offer a beneficial 'store' of energy during portions of the
> revolution. I always thought that it was total hogwash, but was told by
> an engineer that there could actually be some sense in the
> proclamations, even if he too discounted them.
>
> The idea had something to do with overcoming the 'dead spot' at the top
> of the pedal stroke. As we all know, there is a dead spot in the pedal
> stroke that occurs when the pedals are at 12 and 6 o'clock positions.
> The claimed purpose of these cranks was to store enough energy in the
> rotating crank to allow the rider to get through this dead spot with a
> minimal amount of energy that was 'stolen' from another part of the
> revolution. This was achieved by displacing the energy transfer from a
> direct transmission to a slightly offset point of the rotation. The PMP
> cranks placed the actual pedals at the maximum strength position of the
> rotation (namely at between 2 and 4 o'clock and 8 and 10 o'clock
> respectively) whereas the energy transmission was located at the 'dead
> spot'.
>
> My friend the engineer said that on paper a case could be made for it,
> but he doubted that the difference would be so minimal as to not even
> make up for the difference in the weight of the cranks.
>
> Steven Maasland
> Moorestown, NJ
>
> _______________________________________________
>
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