For one, you don't gain anything but unsprung weight and room for bigger brakes by going to bigger wheels than 17". Sidewalls are stiff enough on good tires.
Another consideration was that if I were to go with 18" wheels, I wouldn't've been able to go wider than 295 in back because the next step up availble in 18" (335) won't fit in the back of the Supra. I wanted to have 275's and 315's.
Now 315's are available, but still not in my favorite tire (BFG g-Force TA KD). But 315/30-18 is indeed available in a Pirelli P-Zero Rosso.
If I had unlimited funds, I'd have two sets of 18's..
Street set would be 18x10 with 275/35-18 P-Zero Rossos in front and 18x11 with 315/30-18 P-Zero Rossos in back.
Race set would be 18x10 with 285/30-18 Hoosier RS303's in front and 305/30-18 Hoosier RS303's in back.
Then I could get some nice AP 14" 6-piston brakes up front too........
You could run 18"s in front and 17"s in the rear. It's not as strange as it sounds - since you probably put the big 14" brakes in the front anyway. This lets you run the BFG tires for the street and track - for those of us w/ a limited budget.
Sigh - wouldn't it be nice to have an unlimited budget?
hmmm - I'd get a set of Fikse's for the street, keep existing wheels but put Hoosiers on them for the track...