A lift does 0 for bigger tires. You can fit the exact same tire with or without.
Sorry let me be more precise. Street driven trucks going to a 265/65/17 which is about a 30.5 in tire...shouldnt rub except at full lock DEPENDING ON THE EDGE OF THE TIRE!!! If it is a street tire you shouldnt rub.
My 265/65/17 a/t rubbed very little with the lift...so I imagine it would have rubbed more without. My 265/65/17 m/t rubbed like a some biatch. My current 265/70/17' M/T required a good amount of trimming and grinding.
If you are basing your "FACT" on your michelins which are 30.5 in your sig...then duh...your street tires wont rub cause it doesnt have the hard edge some a/t's do(which is what a terra grappler is). So in your case a lift would do nothing for clearance.