A question,  What is causing the flats - what is found after inspecting the
tube / tire.

The reason for the question is that in some experimantals calling for
tubeless tires,  guys are inserting tubes for the belts and suspenders thing
and flats become quite common.  The culprit is sheared valve stems due to
tire spin on the rim.

The talk of underinflated tires failing suggests to me that underinflation
might be the root cause and spinning of the tire resulting in valve stem
damage might be the actual cause of the failure.

Lowell,

 

There have been very few instances of sheared stems.  The usual consequence of extended use with an underinflated tire is excessive sidewall flex and tube wear along the side.  This weakens the tube and most often produces pinhole leaks in the weakened areas or just outright tube side failures. 

 

The 235, 320/360 wheels and Legacy nose wheels are not designed for tubeless tires.

 

It could very well be that Lancair's inflation recommendation is on the low side since underinflation is a relative term.  Dan's 25 psi is definitely underinflated and perhaps the 42 psi for a 320/360 may also result in underinflation.  At 55 psi and 1800# gross weight, about 600# per main, a main tire patch is about 11 square inches. At 35 psi that patch increases to 17 sq. inches. Thus, with a fixed tire width, the sidewall flexing is quite pronounced as the design tire profile has collapsed significantly.