Tires used in super mileage competition....
Michelin makes a special tire in France for the eco-marathon races (these aren't available to the public, not easily at least). It's clincher bike tire but, it's a radial ply. Crr is claimed to be .001 (1kg/ton) and if I recall inflation pressure is somewhere around 50psi (as opposed to a skinny road bike tire which is >100psi).
The tires are super light and super flexible, but VERY susceptible to puncture. I'm not 100%sure of the name, but I've always seen them referenced as eco-marathon radials. They're identifiable by their wide rolling surface and light blue sidewall (
http://web.student.chalmers.se/group...Eco08/Eco6.jpg - random google picture with them)