They were designed for european ssports cars/coupes/sedans, the main reason the tires don't go over 285 in 18" (315 in 17") form is because of the higly directional tread pattern; which probably wouldn't work at all if the tire is too wide. Almost all wide tires I've seen have non-directional grooves for evacuating water (important, as wide tires hydroplane verrrry easily) the GS-D3 has none of these grooves (because the "V" pattern works well when the water doens't have too far to go.)
I dunno, just my $.02