Jarrett asks:
<<Can anyone tell me ruffly what the O.D. of a 600x6 tire is?>>

The FC-IIs on my plane are 15.00" inflated to 45PSI and with about 10 landings. I would allow another 0.25" for production variances an wear. Also remember that a spinning tire gets "Bigger" in diameter due to centrifugal loads.

Regards
Brent Regan