I've picked up a pair of 5-spoke carbon clincher wheels, they seem to be just a tad larger in diameter than 700c.
I have tried 700x25c Hutchinson, Panaracer and Maxxis tires.. all folding tires, but none of them seem to be able to even get one bead onto the wheel.
I know Michelin and Zipp tires are usually tighter fitting, are Continental, Schwalbe or Vittoria tires any easier fitting?