Regarding spare tire, I have a few questions.

..what is the max size wheel/tire i can have in standard space. And, in what situations is that not going to work (2005, sport v8). Current stuff is 285 x 17

...what are the downsides to driving with my spare that i currently have that is not obv much smaller but stopping when i'm in towing distrance

...ABOVE ASIDE, tell me about having the tire on roof vs. back end vs. keeping under carriage tire. Do you guys just put the tire on the back when you are going out, or leave it there all the time? If on roof, i get it in terms of why, etc... If you don't use the under car option, what do you use the space ffor?