I use the GoodYear Flight Custom III, 5.00-5, 6 ply.
This is a common tire available through many sources, Lancair, ACS, etc.
It costs twice as much, but lasts twice as long -translates into fewer tire changes.  The tread gives me about 350 hours.  It is a much stiffer tire than the original, which could be an issue if you are using the original Lancair donut shocks.  The cross section is more squared-off, but didn't cause any interference issues.
Chris Zavatson
N91CZ
360-std