Re: [CR] Phil disk brake, Vitus 172

(Example: Framebuilding)

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Date: Tue, 6 Jul 2010 13:07:34 -0700
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Thread-Topic: [CR] Phil disk brake, Vitus 172
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From: "Mark Bulgier" <>
To: <>
Subject: Re: [CR] Phil disk brake, Vitus 172

Harry Travis wrote:
> As frames and forks go out of
> alignment, and the curved fork has been mandrel-bent so it visibly
> bends further in response to road shock, might there be anything to
> changes in instantaneous bending resistance of the fork blades
> after much use?

Nope. Frames do not "go" out of alignment unless the material is stressed to the yield point. No rider is strong enough to make a frame yield by normal pedaling; even hitting potholes at 50 mph is extremely unlikely to cause the frame to permanently bend or "take a set" (Although there can be some micro-yielding in individual crystals, this doesn't affect the bulk properties or alignment)

If normal riding stressed the frame to anywhere near its yield point, the fatigue endurance would be measured in days not decades. Even the craziest ultralight record-attempt frame, so light it's meant for just a few rides, will not yield or go out of alignment in use.

That includes fork blades -- they do not increase their rake or offset in use, unless you are referring to flexing as you hit each bump? That is a temporary deflection and the steel returns to right where it was after the load is removed; it doesn't take a permanent "set".

Mark Bulgier
Seattle, WA USA