For a given force and constant tube thickness, the longer the tube the more the flex. The shortest distance between two points is a straight line. Therefore, there is more flex in a curved fork blade than a straight one. There's still a question of what is the amount of blade flex compared to the crown flex. It may be insignificant, but if you ride without your hands, to remove most of the weight from the front wheel/forks, then you can see the blades really bounce on rough pavement. Perhaps the blade flex is negligible compared to crown flex, especially when the blades are only a little over 12" long. Without the Reynolds "flex-o-meter" to determine directional blade displacement with a measured force, we can only have considered opinions. If we look, as a comparison, at a modern aluminum crown/steerer with carbon fiber blades, you do in fact get an easier ride (I got one in here to paint and it had a very large bubble of air just barely beneath the surface, but surprisingly, it had several thousand miles without catastrophe -- but that's for another day), which would suggest that the blades do flex. Take a full carbon fork and the ride is even smoother, which suggests that both the crown and blades, flex and absorb bumps, and therefore a curved blade may well possess shock absorbing qualities.
My nickel's worth, based on observations, and considered opinions.
A blessed Christmas.
Kindly, Steve Dahlquist Velochrome Frameset Painting V 559-592-6367 F 559-592-2585 C 559-967-3318 steve@velochrome.com 22582 Carson Avenue Exeter, California 93221 http://www.Velochrome.com
----- Original Message ----- From: NortonMarg@aol.com To: tullio@TheRamp.net ; classicrendezvous@bikelist.org Sent: Wednesday, December 24, 2003 11:43 AM Subject: Re: [CR]The shape of fork bends in the old days
In a message dated 12/24/03 8:56:18 AM Pacific Standard Time, tullio@TheRamp.net writes:
> Your example above about the Raleigh fork illustrates this. You state > "with > the wheel pushing straight up on that . . ." However, the fork does not > flex upward over bumps. It flexes rearward. The fork is cantilevered off > of the frame and its pivot point is the crown. The steerer must bow in the > opposite direction (forward) to permit the movement at the crown. >
I think it can be shown that the fork flexes in BOTH directions, not just rearward and not just from the crown. If the blades are really stiff, then is will flex mostly at the crown end, but older blades are really pretty flexible. Stevan Thomas Alameda, CA
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