  The evolute of a plane curve is the envelope of its normals. Replacing the
normals by the lines that make a fixed angle with the curve yields a new curve,
called the evolutoid. We prefer the term ``skew evolute", and we study the
geometry and dynamics of the skew evolute map and of its inverse, the skew
involute map. The relation between a curve and its skew evolute is analogous to
the relation between the rear and front bicycle tracks, and this connections
with the bicycle kinematics (a considerably more complicated subject) is our
motivation for this study.
