Some NON-circular wheels with constant width...
Reuleaux triangle. Reuleaux pentagon and heptagon.
see http://www.maa.org/mathland/mathland_10_21.html
Ivars Peterson's MathLand

A Reuleaux triangle is used for the rotor in rotary engines and for a special type of drill that creates square holes.

Try this Very Cool link: http://www.cut-the-knot.com/Curriculum/Geometry/CWStar.html
Note: Barbier's theorem states that all shapes of constant width D have perimeter pD. next