MPG effect of 3.92 rear end

[Kooch80]

been trying to convince many the lie o meter is not right. some closer than others but it's just a gauge or guess at what mpg you are getting. helps to learn driving style not a accurate number. hand calc is the only way.

I usually have calculate as well. On the picture I posted it was off by 0.2mpg. have calculation was 17.4. the closest in accuracy I've had on a Ram truck

 

[GRAYWOLF]

been trying to convince many the lie o meter is not right. some closer than others but it's just a gauge or guess at what mpg you are getting. helps to learn driving style not a accurate number. hand calc is the only way.

It appears to be an average of the last xxx number of Miles, not the whole tank.

Sent from my SM-G965U using Tapatalk

 

[ExcursionDiesel]

It appears to be an average of the last xxx number of Miles, not the whole tank.

That's my guess as well. Seems to be a 300 mile rolling average. To get an accurate estimate of a trip, reset the mpg average screen when you depart.

People with the 3.92 need to understand that the Hemi has a sweet spot at 1800-2000 rpm. Running 80mph puts rpm up around 2200 and mileage drops a lot. At that speed, aerodynamic drag gets way worse as well. My 3.92 truck gets rated MPG at 65 on flat ground or 55-60 with some hills. It drops from 21 down to 15-16 mpg running 80mph.

 

[SilverSurfer15]

That's my guess as well. Seems to be a 300 mile rolling average. To get an accurate estimate of a trip, reset the mpg average screen when you depart.

People with the 3.92 need to understand that the Hemi has a sweet spot at 1800-2000 rpm. Running 80mph puts rpm up around 2200 and mileage drops a lot. At that speed, aerodynamic drag gets way worse as well. My 3.92 truck gets rated MPG at 65 on flat ground or 55-60 with some hills. It drops from 21 down to 15-16 mpg running 80mph.

Yep This is true for pretty much any engine/truck combo. At least for gas v8. Mine was similar although I could never get over 18.5ish hand cal, I assume with the 33” duratracs it’s impossible to go much higher. Makes sense a lighter highway tread would pick up about ~2

 

[ExcursionDiesel]

Yep This is true for pretty much any engine/truck combo. At least for gas v8. Mine was similar although I could never get over 18.5ish hand cal, I assume with the 33” duratracs it’s impossible to go much higher. Makes sense a lighter highway tread would pick up about ~2

The Limited's air suspension lowering the truck on the highway and the less aggressive tires both help.

 

[Timeless]

The Limited's air suspension lowering the truck on the highway and the less aggressive tires both help.

Curious why it does not go to the lowest setting...

 

[EGD]

After a year, the DIC can be off for me, .5mpg to almost 1mpg. It overly optimistic.

 

[Cravenfan]

Curious why it does not go to the lowest setting...

I believe the, "exit/entry" mode is on the bump stops...would be a very rough ride.

 

[screamin chicken]

3373 on my 2021 Ram Limited with the 3.92 and I'm getting 14.9 in the city , and at 55 mph on the. Interstate Im getting 15.1

 

[Neurobit]

3373 on my 2021 Ram Limited with the 3.92 and I'm getting 14.9 in the city , and at 55 mph on the. Interstate Im getting 15.1

Even with a 3.92 that’s pretty low, specially if you’re driving 55 MHP...

 

[Scram1500]

Lifted with big tires? I get in the 20s when traveling at 55-65

 

[1ramrunner]

I have read most of the posts in this thread as I am facing a decision on an upcoming purchase.

I have a 2009 Dodge Ram 1500 with 30,000 miles. It has a Hemi, Crew Cab, 4x4, 3.92 gears and sadly a 5-speed auto. My mileage has never really been good, mostly 15 to 16 with very little city driving. The mileage is low because of MPG and I'm considering replacing it with a 2021.

I really like the looks of the Rebel, but mileage is awful. I looked at the Big Horn, but with all the options I would want, I am priced into a Larime. I am torn between Hemi and Hemi w/ Etorque and 3.21 or 3.92. I am also considering ORG just because of the look, but I'm considering backing off if it will hurt MPG.

From this thread and the other relating to the 3.21 and 3.92 comparison, here are my initial takeaways:
Since I never tow - 3.21 has an advantage
If I go with Etorque and 3.21 - won't the added electric power help get started?
I drive mostly hwy, but with hills - could lean to 3.92
Hwy speeds will be over 70 which favors 3.21 over 3.92 with simple math
After reading posts about MPG declining with higher speeds and 3.92, I believe the higher RPM's are out of the "sweet spot" of the Hemi which means the lower RPM's at higher speeds with the 3.21 should greatly improve MPG in hitting that "sweet spot" for the Hemi

 

[BowDown]

18.3 mpg 80% city 20% highway





Now at 10K miles and at 18 mpg still 80/20 city highway.
Hand calc is 420 miles per tank, 23 gallon to refill comes out to 18.26 mpg
I average 420-430 miles per tank

 

[Willwork4truck]

1ramrunner: Gas mileages being reported are all over the place for sure. Once you lift and add bigger tires you’ll take a hit no matter what gearing. Since you said you have hills, that favors 3.92. Also the reported “off the line” favors 3.92, as well as any heavier payloads with your reported hills.

I went with 3.21 cause’ I drive mostly flat terrain, don't tow and the truck she liked came with 3.21. I was favoring 3.92 just to give me a bit more flexibility as far as the truck’s usage, and I still like that gearset. However the biggest factor was which truck did she like better? So in your area, are trucks that you really like and are well priced available in either gearing?

In the long run, if mpg’s different are a big factor, I wouldn’t even buy the hemi. It doesn’t get the best mpg’s of the big 3 companies engines, you have to want it because of the truck that it comes with. Ride, tech, appearance is what sold us, not gas mileage.

Lastly, I can’t see the e-torque with 3.21’s being very helpful unless you tow. Spend the option cost money on gas with a 3.92. All of this IMHO.

The image below is our Limited 4x CC at 70 mph avg over about 200 miles on a mostly level I-40 with 2 occupants and 3.21 gears. My son has the identical hemi powered truck, with a 6’4 bed and he gets 17 in the same conditions with 3.21’s as well. Go figure.

 

[Willwork4truck]

3373 on my 2021 Ram Limited with the 3.92 and I'm getting 14.9 in the city , and at 55 mph on the. Interstate Im getting 15.1

Very narrow range that is. Usually city is 4-5 different.

 

[Kurtislowe68]

I have ‘21 5.7 etorque with 3.92 gears. I installed leveling kit and moved up to 275/65 on factory wheels. Not much level interstate where I live in Louisiana but I usually average about 14ish on highway and in town driving. On highway I usually run about 73-74 mph on cruise. But I didn’t buy this truck for fuel economy, I bought it for the look with bigger tires.

 

[Kuzi80]

I do 99.9% city driving and I have the 3.92 on my 2019 Ram. My MPG is approx 13.5mpg right now but I am only at 220 miles so the engine isn't even broken in yet.

I recently purchased a 2019 Ram 1500 with the 3.92 and I average 13.5mpg also at 40K miles. I previously owned a 2019 with 3.21 which averaged 18mpg. There is definitely a difference in driving experience. It would be great to average closer to 16mpg. Considering an aftermarket tuner to see if that helps any.

 

[BigD]

My truck in completely stock. No mods whatsoever. 3.92 gears with etorque. I average around 18 mpg with a 50/50 mix of city/highway.

 

[PorBoy]

Shoot my oldie 2019 with 3.92 gears and the lift I was averaging 9 mpg lol.