10.5 on race suspension is the biggest I have seen in the front. 12s in the rear have to be really dialed in, custom, to get it to fit.
I have 305s in the back on 18x11 and could not fit another inch. I have trimmed some plastic too.
Track / Autocross setup: Forgestar F14 (21.8lbs & 23lbs)
Front: 275/35/18 Continental slick on 18x10, Rear: 305/35/18 RA-1 on 18x11
Drift Setup: Front: 275 Continental slicks, Rear: 255 Michelin PS2 street tire
Laguna Seca previous record - 1:49:498