The S is even roomier than you know, as just drove my recently purchased P85 from Seattle to Iowa with four 21" rims/tires, plus two spare 21" tires (no rim)...one in frunk and the other one joining the full set in back. So I was fully prepared for a flat (once someone showed up with a jack)!
lol wow, did you drive out there to buy the rims/tires and drive them home? Definitely a fun road trip and a ton saved on shipping if so.