Bicycle model in chapeter 10

[fenaux]

Many thanks for this fantastic book

Just to make bicycle model calculation more clear to me.
Assuming both wheels are on the same circle of radius R (that is exactly the no slip assumption)
then pure trigonometry gives w / R = tan(alpha) (as both radius are perpendicular to wheels)
and then with beta = d / R
we obtain beta = d / w * tan(alpha)

otherwise the relationship beta = d / w * tan(alpha) at the beginning seems to come "out of the hat".