It is not uncommon to see in a science museum a bicycle with
square wheels that rides smoothly over a washboard-like
surface made from inverted catenary curves (e.g., at the [Münich museum][1]).
The square wheel may be generalized to any regular polygon (except the triangle),
which rolls on a similar curve without slippage.
Here, for example, is a nice [Mathematica demo][2].


My question is: For which wheel shapes does there exist
a matching road shape that permits the wheel to
roll over it without slippage so that:
(a) the wheel center remains
horizontal throughout its motion,
(b) the wheel can turn at constant angular velocity,
and (c) if possible, the wheel center also moves at
constant horizontal velocity?

The square satisfies (a) and (b), but only regular hexagons
and beyond satisfy (c).  If you've experienced a
square-wheel bicycle ride, you can feel it jerk because (c)
fails to hold.
It would be interesting to know the class of closed wheel curves
that satisfy (a) and (b), and also those that in addition
satisfy (c).  For example, must all (a,b) curves be star-shaped from the wheel center $x$?
(*star-shaped*: every point of the curve is visible from $x$).

This is probably all known, so an appropriate reference
may suffice.
I don't quite know how to tag this; please retag if you know better.


  [1]: http://www.mathstube.org/index.php?option=com_hwdvideoshare&task=viewvideo&Itemid=2&video_id=257
  [2]: http://demonstrations.wolfram.com/RegularPolygonRollingOnACatenary/