Re: [CR]Curved crank sets...Why

(Example: Framebuilders:Richard Moon)

Date: Sat, 1 Jul 2006 11:30:21 -0700
From: "Kurt Sperry" <>
Subject: Re: [CR]Curved crank sets...Why
In-Reply-To: <094001c69cd9$a7855fd0$0200a8c0@HPLAPTOP>
References: <094001c69cd9$a7855fd0$0200a8c0@HPLAPTOP>
cc: CR <>

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 <> 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
> _______________________________________________