right now i have 285/75r16 and need to get new tires im lookin for better fuel economy when i went from stock to the 285 it went up hand calculated. at 75 right now im runin around 2050 rpm which went down from 2400 i know anything over 2000rpm uses lots more fuel so if i went to a 35 12.50 would i get better mileage or would the extra mass of the tire kill the mileage. bout 80% of my drivin is highway and im running about 18mpg right now

the only stuff as of now that i have done to the truck is in my sig.
soon to have hx40 or hybrid turbo 5x12 injectors and adjusted timing

thanks im just lookin for a lil imput b4 i kill my self over a stupid tire mistake

---AutoMerged DoublePost---

its gonna be tuned for around 500hp by the time im done still de-siding on the turbo tryin to run a single with fast spool to keep from wasting fuel i love blowin smoke when playin with ppl but im an old person driver just want the power for the strip

 

If you want better mileage, I doubt a bigger tire will help, the extra mass would most likely hurt it. Smaller tire with a higher gear ratio in the back end would be the best bet. What gears do you have right now?