Re: [CR]Thoughts on drilling track forks

(Example: Humor:John Pergolizzi)

Date: Sat, 16 Dec 2006 21:00:52 -0800
From: "Kurt Sperry" <haxixe@gmail.com>
To: john@os2.dhs.org
Subject: Re: [CR]Thoughts on drilling track forks
In-Reply-To: <4584B14D.1020603@new.rr.com>
References: <121620062018.602.458454AD000DF1CA0000025A2207020853020E000A9C9D0A08@comcast.net> <75d04b480612161230t15b261f7h5c85071348ae87b2@mail.gmail.com>
cc: classicrendezvous@bikelist.org

That is essentially what I had thought, that the blades themselves deflect under braking. It even appears like that is what is happening to me from the saddle, but when I made that observation onlist some time back when discussing the effect of fork bends vs. straight fork blades I was told that the actual flexing was essentially all happening in the fork crown and steerer. This was unrefuted at the time so I assumed it to be true. The bending moment is certainly greatest up near the lower fork race under braking so this seemed plausible to me.

Kurt Sperry Bellingham WA USA

On 12/16/06, John Thompson <JohnThompson@new.rr.com> wrote:
>
> Kurt Sperry wrote:
>
> > Isn't it a consensus view that the actual deflection apparent while
> > braking- and hence presumably the attendant stresses- actually take
> > place above the fork blades? If this is in fact the case, I'd expect
> > whether the fork blade sections are round or oval to be essentially
> > immaterial to braking.
>
> No; the momentum of the bike provides a forward force which is resisted
> by the tire's contact with the ground. This is transmitted through the
> hub to the fork, and flexes the fork blades backward toward the down tube.
>
> --
> John Thompson (john@os2.dhs.org)
> Appleton WI USA