This is a good topic for lots of car guys. Here's my take: any car worth owning should have bigs on the back and littles on the front. My wife's '69 Corvette has 295/50 rear and 265/50 front. If you carry the smaller tire, you'll kill the limited slip by using it on the rear and if you carry the larger one, it won't fit on the front. My '68 suffers from the same thing plus no real trunk room, so now what? Most cars my whole life have been the same, Model A hotrod, dropped mini truck, dropped Blazer, dropped full size Chevy truck, all had staggered tire sizes as does my wife's Roush Mustang and the previously mentioned fastback and Corvette. I should carry fix a flat, but haven't yet. I do carry a cell phone, but here in Southern Oregon, that's not always 100%. Here's another point to consider: I've had a flat tire 2 times since I started driving in 1978, once in my parent's Honda Civic in 1980 (bias ply tires) and once about 3 years ago when a rock the size of an trash can dropped off a hill in front of my F250, blowing out the sidewall of a nearly new tire. I also rode sportbikes for years and they never had a spare with them. Live a little and keep good tires on your car I guess.