Actually, for accuracy, Wikipedia got this one wrong. Here's a better description of the wheels:
Spherical molecules called buckyballs made of 60 carbon atoms each serve as the big rear wheels. Due to chemical attractions, these wheels nicely grip the "dragstrip," which is made of a superfine layer of gold rather than pavement. For the front wheels, the scientists opted for a less sticky compound called p-carborane.
Tour's group built nanocars before with buckyballs as all four wheels, but these autos hug the road too tightly and require temperatures around 400 degrees Fahrenheit to get rolling. Nanocars with all p-carbonane wheels, on the other hand, slip and slide as if on ice, said Tours, making them difficult to image and study.