I am buying new tires for my DD Tahoe. Was thinking about going up a size or two, but how much will changing tire size affect my MPG? Seeing how a am driving a gas sucking pig already, I dont want to kill my MPG much more than I have too. currently I get anywhere from 12-13mpg on average. Any idea how it could be figured out from one tires size to the next as far as how my MPG would be effected? Current I have some Kelly Safari MSR tires that are 265/75/16's. Kellys specs are 31.9 tall x 10.7 wide. I got a set of 17's cheap so I will be getting new tires for these. Was looking at Goodyear Silent Armor tires in either 265/70/17, 275/70/17 or 285/70/17. The specs on these are: 265/70/17 = 31.7 x 10.7 revs = 650 and the weight is 48# 275/70/17 = 32.2 x 11.0 revs = 645 and the weight is 53# 285/70/17 = 32.8 x 11.7 revs = 633 and the weight is aroudn 58# Would there be a huge difference in MPG performance between the (3)? Or not much at all? The sizes are very far apart, but the weights change a decent amount from the 265 to the 285....... Anyone?