Axle ratio and mpg

[ChrisRCNY]

I have a 4wd 08 with 3.73 gears that will likely be getting a used rear diff swapped in, due to severe ring & pinion slop. I don't object to swapping the front diff, or getting a new tune from 5star.

Is mpg improved much going to 3.55 or 3.31 gears?

 

[ExplorerTom]

On my 3.55 geared Explorer, I swapped to 4.56 gears. Mileage remained roughly the same- went down maybe 1/2 mpg. Towed like an ox and jumped off the line though.

Lower RPMs don’t always equate to higher MPG. An engine is most efficient at peak torque.

 

[coolzzy]

Not worth the loss in tow power to save a tenth of a mpg. These are heavy vehicles, if you are getting better than 12mpg in town or 15 on the highway with the 5.4 motor, you're doing all right.

 

[johnboneske]

I agree... Don't lower the gear. I doubt you will see any improvement, in fact I think the opposite will happen. These things aren't RPM screamers, but reducing the RPM to save fuel can sometimes actually hurt you since your making less torque. I'd actually consider going to a higher gear if it was me and had to do it. If you ever have to tow anything with a decent amount of weight you will want the gear. Just my $.02

 

[coolzzy]

Agreed if you are swapping gears, go to 3.73, it will get better or the same mpg in town but pull much better.