Was thinking about my rear end differential gear ratio from 3.73 to 4.10. I believe my truck came with 3.73 stock. I plan on going to either 35" or 37" tires. Will this increase my MPG or decrease? Any suggestions or insight on rear end gears. Thanks
With the 35" tires you will have a decrease in mpg due to the additional rotating mass. You will also notice the truck will be running at a few hundred rpms lower than previously at the same speeds again due to the rotating mass and power needed to turn them.
By increasing your rear end gears you will just be putting the truck back in to more of a happy zone as far as your rpms go, thus making it more responsive. It basically makes up for the loss of rpm. Will make your highway driving gain a little bit of mpg, but potentially can take away from around town. take a look around here for a good read :thumb
I would leave the stock gears in it, i made this switch in my 06 cummins sittin on 35s and it didnt help me at all, mpg was slightly worse and my 60' was still the same as the track. Save yourself a couple thousand $$$.