Am I right with my understanding of the gear ratios tire size

[Augiedoggy]

So my truck currently has 3.92 gears as Ive discovered today and 31.5" stock size tires (I am at 1,260rpms at 45mph) ... I currently get right about 30-31 mpg at 65mph according to the computer. Am I right in thinking that if I install the 3" spacers in the front and 2" in the rear and 33" tires I will still have a lower gear ratio that the same truck equipt with 3.55 gears and stock tires and therefore still possibly retain great or possibly even better mpg? As it stands now the truck sits very low for a 4x4 and I dont want to go nuts but because of the long wheel base the wheels look funny to me being so small. Ive read the stance may cost me a couple mpg and I plan on going with mild AT tires like I have now just a couple inches bigger.

Years ago I had a lifted jeep wrangle and when I went from 31" tires to 32" I actually lost the ability to hold high way speeds in fifth gear until I swapper the 4.10 gears with 4.56 gears which increased my MPG dramamtically as well as made the jeep handle more like stock powerwise and corrected my speedometer so my thinking is the larger tires will make the truck behave as if it had stock tires but something in the middle like 3.73 gears right? I also had a gen 2 once with 7" lift and 4.56 gears with 35" mud tires and although it was "cool" at the time it made the truck impractical for my adult needs as they changed lol... I know im old.

 

[Augiedoggy]

also... I have the red airbags inside of my rear coil springs. Can this still be lifted with 2" spring spacers? I'm not concerned about offroading here.

 

[Augiedoggy]

I just learned I need to test at 55mph since it may not be in 8th gear at 45.

 

[Tremper126]

bigger tires = more weight
I have the 3.55 rear and when I went from stock tires to 35’s I couldn’t tel a power difference at all but my mpg dropped a few ticks. I tow frequently so a true mpg reading on the highway isn’t anything I could achieve

 

[Augiedoggy]

bigger tires = more weight
I have the 3.55 rear and when I went from stock tires to 35’s I couldn’t tel a power difference at all but my mpg dropped a few ticks. I tow frequently so a true mpg reading on the highway isn’t anything I could achieve

Thanks, I do understand the tires are slightly heavier but thats rolling weight too so im not expecting that to have too much effect especially since Theoretically the truck with 3.92 gear should have room for mpg improvement with lower RPMs from bigger tires. I guess I will just have to do it and find out it it cancels itself out as far as mpg but its slightly more sluggish which isnt an issue for my truck being its tuned. also the 35s seem a lot heavier than the 33 ive had compared to when ive gone from 31 to 33 so im hoping thats the case here.

 

[Augiedoggy]

well I think I figured out why my truck seems to sit so low.. https://www.ecodieselram.com/forum/threads/is-my-truck-lowered.5303/