I've fit everything from 185/14's to 225/15's on 15x9's in the car with the 1 in the trunk, 1 on the back package tray, and 2 vertically in the passenger seat method. I've done it several times with several different sets of wheels and while it requires some finesse, it'll work. The only catch is that my '99 has to have the windblocker removed from the back if I decide to do this, so if you have one, bring a screwdriver. I'm not sure how that'd go with the brace across that area that's on select Miatas too.
