For Every Wheel, There's a Road.

clipped from www.maa.org Riding on Square Wheels It turns out that for just about every shape of wheel there's an appropriate road to produce a smooth ride, and vice versa. Interestingly, triangular wheels don't work. As an equilateral triangle rolls over one catenary, it ends up bumping into the next catenary clipped from thinkingpictures.blogspot.com