255/45s or 275/40s
I would imagine the 275 would offer slightly better grip, but they are smaller overall diameter by about 1/2" Unless you have a tune your speedometer will be off slightly [nothing dramatic, but not accurate]
I ran 275's all the way around my 2003 Mach 1 and it tracked badly in the ruts - noticably worse than the factory 245's. However, I will not hesitate to replace the factory 235's on my 07 Mustang GT with something wider. I'll likely go 245's in the front and 265's in the back (on my 18 x 8.5 factory fan blades). With an 18 x 9 wheel, a 275 width tire would be great.
One of these days Im going to flash it with 3.55 instead of stock with my X3 and see if it changes mph per rpm registered.
In your flasher there should be an option for tire revolutions per mile which will correct your speedo. The revs per mile is available in the Tire Rack specs for your tires.
I love the Nittos..... I was a little hesitant to try them but I'm very glad that I did. Traction, well that's maybe not the fairest question- with the blower and 4.10 rear gears you have to learn to drive the car nicely in the first 3 gears LOL but overall they're pretty dang good IMO.
I run 275/40/18's on 18x9's all the way around and have had no problems with tracking.
Currently have ContiExtremeContact All Season, and don't recommend them for twisty handling traction in dry conditions. They are very soft and squeel pretty bad. I do say they handle snow and ice quite well, and since that is where we are now, that is a good thing. Even in HEAVY rain they are outstanding, so I suppose you can't have everything.
I am shopping for my "spring shoes" right now...
Currently have ContiExtremeContact All Season, and don't recommend them for twisty handling traction in dry conditions. They are very soft and squeel pretty bad. I do say they handle snow and ice quite well, and since that is where we are now, that is a good thing. Even in HEAVY rain they are outstanding, so I suppose you can't have everything.
I am shopping for my "spring shoes" right now...



