I just recently changed my 03 SuperCrew tires from 255-70 16 to 285-75 16. I know I was going to lose some gas mileage but I think I lost too much. Went from about mid 15 mpg to under 12 mpg. What does anyone think the norm for this is...I drive alot of highway on the weekdays and that is what I am basing it on. Anyone could help let me know.

 

Did you correct your speedo for the larger tires? If not, that can account for a good bit of the low MPG.

If you do mostly highway driving, I would not expect your mileage to drop quite that much.