I went from the stock 265/65/17 and getting 22.2 mpg at 65 mph to 265/70/17 Terra Grapplers and now get 18.5 at 65. I know My tire size changed my dash reading by like 1.2 mph or something, but that doesn't account for nearly 4 mpg. I knew it would affect it some just not that much. I guess it is what it is now!!!