Thanks for all the good wishes and advice!
We have been busy the last few days preparing a 5 minute video with the status of our vehicle, this video is due at DARPA a week from today. Will get some pictures to share with you soon.
Based on the feedback provided here (thanks!) and reading an interview with Bob Land a few years ago (thanks for the pointer) here's our initial take on tire requirements:
Diameter: around 31 inches
Tread width: 8-10 inches
Plies: at least 6
Load Range: "C" or "D"
Wheel radius: R16 (stock '99 VX)
Tire pressure: 25-30 psi
Puncture resistance: tire sealant
Opinions?
Art