Tire size affecting mpg

i know that bigger wheels without changing the gears usually diminishes the mpg, but what about smaller ones? from a stock 265/70/16 to a 275/60/17, the diameter of the wheel with tire goes from 30.6 inches to 29.9 according to the calculator at Dead Link Removed itz not that much, but if you were to go wtih a smaller tire, would that improve gas mpg? or are the 30.6 the optimal size for our explorers?

 

[CBoug76]

Isn't the Stock Tire Size 255/70/r16?

 

[CBoug76]

Your Speedometer reading with the Non-Stock tires is 2.0% too fast.
When your Speedo reads 60 mph, you are actually traveling 58.8 mph.

http://www.miata.net/garage/tirecalc.html

 

[jssong]

yeh.. they were stock 255/70/16, but ive had 265 on for awhile. but regardless of the speedo, what about gas mpg?

 

[Robert]

I do not believe that going from a 30.6" tire to a 29.9" tire is going to be a large enough change to see any affects on your gas mileage. Maybe if you have the average MPG of your last 20 fill-ups and then took the average of your first 20 fill-ups with the smaller tires, you might see .2 MPG difference. Do it again and the results could be the opposite. I went from a 30.5" tire to a 31.7" tire and saw no discernable change in my mileage.