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

(Example: Production Builders:Tonard)

Date: Sun, 02 Jul 2006 16:18:55 -0700
From: "John Jorgensen" <designzero@earthlink.net>
To: classicrendezvous@bikelist.org
Subject: Re: [CR]Curved crank sets...Why
References: <MONKEYFOOD7bvAOopFa0000368b@monkeyfood.nt.phred.org>
x-mac-creator="4D4F5353"

Kurt Sperry wrote in response to a Steven Maasland post that added a comment about straight fork blades..

That said, straight bladed forks, irrationally perhaps, offend my eye no matter it seems how many times I see them. Has no engineer ever offered a cogent rationale for the curved blade other than on purely aesthetic grounds?

Can't speak for the modern stuff, but fork blades in the CR timeline were in the majority of taper gauge, the processing of the tubing yields a conic section where the wall gets much thicker near the dropout, from an old Reynolds 531 cut-a-way display set, about 3X thicker adjacent to the dropout. Much easier to bend a radii into a tube of thicker wall than a thin one without visible localized distortion. The idea of blades deflecting in the vertical plane is urban legend within normal rake profiles. the deflection happens at the crown or near the crown. Did some deflection tests while in school just for argument's sake.

Why the convention was to achieve fork rake with a curved blade instead of an offset crown? Don't know that one. In the past I bet manufacturability probably favored the curved blade. Easier to adjust rake by bend rather than retool.

Aesthetics of a straight bladed fork are a different matter and generally beyond the CR list timeline, but functionally probably equal.

John Jorgensen
Palos Verdes Ca USA