Ideal RPM range for fuel economy

[Wackiness1405]

What rpm range are you seeing for the best fuel economy? Just got a 2023 with 5.38s and it runs around 2400 rpms at 50mph, which is higher rpms than I'd like to cruise at based off my experience with other diesel equipment. Was contemplating putting 4.10 gears in at some point.

 

[Gabe]

What size tires? You mostly driving on the street ?

 

[USMC]

I am running 2350 RPM at 55 MPH with 5.38 gears and 35 inch tires in 5th gear (.78). We have traffic speed indicators on the side of the road so I could check my MPH with some accuracy. I just happened to check my numbers on my way home.

With 29 inch stock tires I was at @ 2700 RPM at 55 MPH in 5th gear (.78).

 

[Wackiness1405]

Stock tires currently and mostly on gravel roads and some muddy pivot drive ways but those are a 1/4mile at most.

 

[Wackiness1405]

I am running 2350 RPM at 55 MPH with 5.38 gears and 35 inch tires in 5th gear (.78). We have traffic speed indicators on the side of the road so I could check my MPH with some accuracy. I just happened to check my numbers on my way home.

With 29 inch stock tires I was at @ 2700 RPM at 55 MPH in 5th gear (.78).

Did you notice a fuel mileage increase at all with the tire change?

 

[Bob R1]

I have a 2024 with 5.38's. I have 235/85R16 Thunderer TracGrip M/T Tires (32") on it.
I drive on County Roads (Gravel as well as Black Top), in Town, as well as Trails.
The best that I can tell with these tires, I am running 10% over what the Speedometer shows. I normally keep between 40 MPH and 45 MPH on the Speedometer. Which should be 45 - 50 MPH on Black Top Highway.
The first tank of Diesel Fuel that I checked got 26 MPG. The second tank was up to 30.25 MPG. More Paved Road, less Gravel Road and Trail's.
In my humble opinion, if you need to go faster than 45 MPH on the speedometer for any length of time. Find someone with a set of 3.73 Gears who wants to swap for your 5.38 axles.
For the driving that I do, the 5.38 Gears work out just fine. I get around very well staying under 50 MPH, actual speed.

NOTE: All that I drove my Roxor with stock tires was the test drive on the dealer's lot, PLUS 50 feet loading it on a trailer taking it to the Tire Shop.

Bob R

 

[USMC]

Did you notice a fuel mileage increase at all with the tire change?

Hey W,

I think I actually lost mileage, maybe from the extra weight of each tire? I will be checking my mileage this week again. My shifting actually remains the same as far as my RPMs go. I was a bit disappointed thinking I may have lost mileage.

 

[Bob R1]

I filled up again this morning. So far I have ran four tanks of fuel through it. I have gotten:
26 MPG
30 MPG
27 MPG

Way better than my Jeep Wrangler has ever thought about.

Bob R

 

[Gabe]

Yes. I think anything near 30mpg is fantastic. About what my AT4 GMC with the 3.0 Diesel does!