on the patch

[Tihol Tiholov]

I'm no accomplished engineer but it seems that Dan is right about 
that formula being overly simple and "tireless".  How about run-flat 
tires?  Not much pressure in there and the contact patch seems not 
too bad at least for a few miles.  Or else, rally tires that can 
support a grown man (or a woman) sitting on one of them, even with no 
rim inside to complicate matters - pretty tough material to be 
ignored.  If pure mechanics was enough, there wouldn't be other 
disciplines like resistance of materials, for instance.

And that puny spare, say 135/70X15 (16 or whatever) has to stretch 
lengthwise down to the axle to cover the same patch as a wide low 
profile tire.  I guess the relationship here is not linear...