I am going with BFG AT's but undecided on size. I will be sticking with the stock 17" Sport wheels and know I will be needing a 1/4" spacer with the 285/70's. My questions are what will be the difference in gas mileage as I commute almost 40 miles roundtrip? I am averaging about 18 mpg now with the stock Dunlops. I know I will get better gas mileage with the 265/70's but how much? Any input would be appreciated.