Riding on Square Wheels

Stan Wagon, a mathematician at Macalester College in St. Paul, Minn., has a
bicycle with square wheels. It’s a weird contraption, but he can ride it
perfectly smoothly. His secret is the shape of the road over which the wheels
roll.

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Stan Wagon rides his square-wheeled trike over a special
roadway.
Courtesy of Stan

Riding on Square Wheels (Science News)

For those of you who might feel this blog neglects geometry, and the inverted catenary in particular.

Quibble: that looks like a tricycle to me — there’s a basket in between two back wheels.