Tire width

ya i have a 275/50/r15 in the back of mine. but i got a mt drag radial. but i notice i had a lot of room back there even now. maybe bigger in the future but its up to you. the more contact on the road the better. also what look you going for. what size rim? im runing a drag with a yokahoma es100 235/r15 up front which looks good. depends i guess on what you plan on doing you your car for weekend driver a 275 or smaller would be fine its up to you.
 
What size come on the new stangs?235? they are ~300hp.
I am running goodyear f1's 225/45/17 all around thinking i can rotate and get somewhat neutral handling when pushing it.
I used to think my 17's were expensive compared to some bfg 15 inchers (and they are), then my buddy picked up a viper, all is in perspective now that i looked those pups up on tirerack....
 
you might be able to fit a 295/50 in the back but you may have to do a little panel beating in the front inner corner of the wheel house and on the suspension bumper bracket. 275/50 or 275/60 is about as big as you can go without having to beat on anything.