yeah, looking more for a minor all-around improvement by reducing unsprung/rotating mass. the FN wheels should already be decently lighter than my OEM, wouldn't mind going to a lighter tire as well. when I say "measured mpg" I recognize that my odometer is off by as much as 10% [285/75-16, roughly 33" currently], and when we took our trip to colorado we peaked on mpg at 17 measured mpg. All that considered, I don't think it's particularly terrible for what I'm asking of it, but it's also bad enough that any minor improvement will help. my normal commute is lots of start/stop, which is about the only area that lighter wheel/tire combo will help efficiency, but the narrower tire can actually hurt rolling resistance depending on the shape of the contact patch, inflation, etc... it's all a series of trade-offs. you're probably right though that I'm worried about pennies and ignoring dollars (so to speak).