en réalisant une projection

le moyeu de la direction, pas de la roue, je suppose

"(EN)The invention provides a motorcycle (50) with hub steering, the axle (2) of the hub (1) being fixedly connected to first support arms (56) and being disposed in such a manner that it can turn with respect to the hub body (3). Second support arms (55) are arranged in such a manner that the front pivot points (60, 61) and rear pivot points (62, 63) lie on non-parallel lines (A, C). Attaching the front wheel (52) in this way results in an improved suspension and increased stability of a motorcycle (50) with hub steering.
(FR)L'invention concerne un motocycle (50) doté d'une direction à moyeu, l'essieu (2) du moyeu (1) étant relié fixe à des premiers bras de support (56) et étant disposé de manière à pouvoir tourner par rapport au corps (3) de moyeu. Des deuxièmes bras de support (55) sont montés de sorte que les points de pivotement avant (60, 61) et les points de pivotement arrière (62, 63) soient sur des lignes non parallèles (A, C). Fixer la roue avant de cette manière permet d'améliorer la suspension et la stabilité d'un motocycle (50) doté d'une direction à moyeu."
http://www.wipo.int/patentscope/search/en/WO1999035028

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Note added at 1 hr (2012-03-16 12:54:00 GMT)
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"RAKE: The angle of inclination with respect to the vertical of the axis of rotation about which the front wheel is turned during the steering process. This is usually the angle with respect to the vertical of the steering head of the frame, but not always. For example, if eccentric bearing cups are used in the steering head to alter the angle between the steering head and the steering stem of the triple clamps, than the rake is the inclination with respect to the vertical of the steering stem. The definition of the rake via the axis of rotation is always true and even applies to non-conventional designs. Typical numbers range from about 20 to a little over 30 degrees, the former for GP-racers and dirt bikes, the latter for cruisers and most vintage bikes. Note however that a relatively well-handling motorcycles have been built (most notably by Toni Foale, a 1970s chassis specialist) with much steeper steering head angles (i.e. a much smaller rake angle). "
http://www.motorcycle.com/how-to/chassis-alignment-basics-34...