I think this is just physics, not a wild theory or funny interpretation of a calculated result. The front wheel contact patch trails or follows the intersection of the steering axis with the ground. When riding there is a backward force on the wheel, applied by the ground, which when the fork is not in a straight-ahead position results in a torque around the steering axis in the direction of the straight-ahead position. If the fork turns a little about the steering axis, this backward force tends to turn the fork so the front wheel is back in line. If the fork overshoots its position, there is a similar centering force on the other side.
With a misaligned bike, I will speculate that the self-centering torque might not be zero at the straight ahead position or be equal in both directions.
Will it be stable? That's a bigger question, but there is definitly a self-centering torque acting around the steering axis.
The reading sources here go way beyond Jobst, to include David Wilson and Jim Papadopoulos and his research team. They've published extensively on this topic, including on the dynamic stability question.
Ken Freeman Ann Arbor, MI
-----Original Message----- From: classicrendezvous-bounces@bikelist.org [mailto:classicrendezvous-bounces@bikelist.org] On Behalf Of Jerome & Elizabeth Moos Sent: Sunday, February 03, 2008 1:09 PM To: Nor Meyer; classicrendezvous@bikelist.org Subject: Re: [CR]Re: headsets & handling
Jobst's theories have to be taken with a grain of salt (or maybe a metric tonne). His book is very useful for building wheels though.
Jerry Moos, who used Jobst's book to build some 650B wheels last weekend Big Spring, TX
Nor Meyer <norbikes@gmail.com> wrote: I recall reading somewhere (Jobst...?) that the bicycle's geometry is designed to "encourage" the front wheel to return to a "neutral" position---that is, in line with the frame----whenever it's steered away from the neutral/forward position. The reason for this is that anytime the fork is turned from the forward position it imperceptibly raises the front end of the bike, thereby raising the potential energy of the bike & rider. The forward/neutral position for the front wheel/fork therefore represents the most stable position, towards which the bike is naturally inclined---- provided the fork can rotate freely in its bearings. Hence the necessity of properly adjusted headset bearings----needle or ball----for care-free hand's off riding. Which, incidentally, allows the rider a superbly nuanced interaction with his/her machine....
Nor Meyer in Iowa