So follow my logic and see if you think I'm in the right ball park on how i'm doing this - - -
GPA:
255/55 - 28" tall tire ---> 6 TB turns =
33.5" floor to top w/w.
KAT:
285/60 - 31.5" tire ---> ? TB turns =
33.5" (I rounded up to make it easier) floor to top w/w.
My tire is 3.5" taller than GPA's.
6 TB turns accomplishes about 3.5" of lift.
So 3.5" / 6 = roughly .6" per turn
So if I subtract 6 turns (3.5"), floor to top w/w. stock should be 30" (33.5" - 3.5")
But since my tires are 1.9" taller than stock (31.5" vs. 29.6") my "stock" height with the 285/60s should be 1/2" less (1.9"/2), so floor to top w/w = 33"

um, - - - that doesn't sound right --
or maybe I just have to have mechanic crank them back as far as they go and then count 18 turns like jmayer mentioned.