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