what is the biggest tire you can put on a 2012 shelby without modifications

 

what is the width of your rear wheel? 10"? probably 305, 315.

bigger isn't always better though - at a certain point you're just creating bulge and not adding extra contact patch.

 

Safely? Find out what your wheel size is and then check the various manufacturers' tire specs for wheel width ranges for different size tires. Remember: larger wheels and tires = more weight = less performance. Also, larger tire OD's will virtual-change your overall gear ratio so try to stick with the OE OD. Changes to the OD will also impact your speedometer.

 

So Nuke, on your 07, does the 275 fit nicely on all fours without issue? I am looking to upgrade mine pretty soon and would like a beefier look than the stock size currently on there.

 

The 275's fit the 9.5" width fine although the wheel can handle a 285 safely. If I had to do it again I'd put 255's up front and 285's on the rear. Those 275's simply tramline too much on heavily truck-driven roads.

I'm not lowered so those 275's have gobs of room. Watch your offset. My wheels are very close to the OE wheel offset.