2021 Ram 1500 Limited 3.92 gears change to road gears

[stormcom]

I have a new Limited with 3.92 gears. I pull nothing and my hwy mileage is 15mpg. Has anyone done a change to a 3.40 or 3.21 and how much did your gas mileage go up. Everytime I start it, it is at least 100 mi trip. It drinks gas like a gasaholic. It is a play pretty and may haul 200 pounds in the back every 3 months. Truck has 5300 miles.

 

[Rlaf75]

I have a new 5.7 Bighorn with 3.21 and I'm getting about the same mpg. I have 500 miles on it now and I'm not using my heavy foot on the pedal either. In my opinion, and this is only my opinion, I dont think the money you will spend on swapping gears will be worth anything in regards to fuel efficiency. Unless you're driving 65 mph on the highway I dont see it improving much if at all. Again that's just my opinion

 

[mikeru]

My 2021 Limited w/3.21 gear gets averages better than 17 mpg when I'm using it for my 25 minute commute each way. With about 80/20 hwy/city mixed driving. I haven't taken it on a long enough drive yet to calculate highway only mileage. It's got just over 2k miles on it. My previous truck was a 2020 Laramie w/3.92 gear. It averaged about 15 mpg on the exact same commute. So I'd say you will see an improvement in fuel economy if you switch to a taller gear. I'm sure I don't need to tell you, but just in case...you'll need to change both diffs if your truck is 4x4.

 

[JohnnyBandit]

I have a new Limited with 3.92 gears. I pull nothing and my hwy mileage is 15mpg. Has anyone done a change to a 3.40 or 3.21 and how much did your gas mileage go up. Everytime I start it, it is at least 100 mi trip. It drinks gas like a gasaholic. It is a play pretty and may haul 200 pounds in the back every 3 months. Truck has 5300 miles.

If you are concerned about gas mileage?..... Why did you get a Hemi?

Does not sound like you are hauling much weight or Hauling A$$.....

Run it and enjoy it.....

 

[Smokey613]

On the highway we average 19-20 with our 3.21 axle. We just completed a 2500+ mile trip pulling a TT that was about 5600 lbs as loaded. We averaged 10.3

 

[KeithP]

At 5300 miles it’s barely broke in. Your mpg should get better, well, a little better. Speed matters, huge drop in mpg from 65 to 75mph (per the EVIC which is not dead on accurate but does give a ballpark average). Changing the gears will make a minuscule difference in mpg but will take tens of thousands of miles of driving to recoup the cost of changing them.

I’m on my 3rd Ram. All three w/3:92 gears the last two w/Hemis. I can’t tell you what my average mpg is/was on any of them. I knew what I was buying and fuel efficiency wasn’t it. They all have served me well and I’ve enjoyed driving them. I will buy another, it will have a Hemi w/3:92 gears and I still won’t track my fuel mileage.

 

[TestPilot57]

Can't possibly imagine the cost will be paid by increased mileage. But maybe - depends on specifics.

I mostly drive 12 miles to work and back, 3 miles in very hilly terrain at 30-40 MPH, 7 miles in light hills at 55 and the final 2 miles at 30 in flat/village conditions. I typically see 14-15 MPG. I took my first trip a month or so ago - around 500 miles on roughly half secondary roads (40-50 mph) and the rest interstate (60-70 MPH). I got over 20 MPG with 35" tires, 2" front level and 3.92 gears. I DO use non-ethanol gas whenever possible (which is usually 91 or 93 octane).

 

[PCT]

I have a new Limited with 3.92 gears. I pull nothing and my hwy mileage is 15mpg. Has anyone done a change to a 3.40 or 3.21 and how much did your gas mileage go up. Everytime I start it, it is at least 100 mi trip. It drinks gas like a gasaholic. It is a play pretty and may haul 200 pounds in the back every 3 months. Truck has 5300 miles.

I get about 15-17 HWY with my 6.4 w/ 4.10's on 35's. But that didnt start happening until about 8k miles. before than I was getting 13-16 mpg hwy... Give it time should get better.

 

[stormcom]

I will just keep driving it. It is a huge cost to change 2 diff's. Someone asked why I bought it. I enjoy comfort. I had a boost 3.5 Ford Platinum with 2 turbos. Dealership said about 1-2 miles difference with the 3.92. It was the right truck and the deal was good. I am getting the front seats repadded. I enjoy it alot. I had 2 2016 ecodiesels that had engine problems at 40k and switched to Ford. My dealer had a 20% off on this truck so I bought it. Thank you to everyone for the answers. Hopefully the mileage will go up around 10k.

 

[hemihustlin]

I would agree with the others that its not fully broken in yet. Load up your box with more than 200 pounds of stuff and go for a road trip that burns a whole tank of gas. That should do it haha
I only started getting good milage after I did my first oil change and went on a long road trip in the hills with lots of accel/decel (engine braking)
21 warlock hemi 4x4 3.92 gears
when I first picked it up I was getting numbers similar to my old 2006 hemi 3.92s which was very bad lol
ever since my oil change road trip I average 16l/100km mixed driving (hand calculated)
just driving on the highway at 100kmh I get between 10 and 12 l/100km depending on the conditions

 

[TestPilot57]

For those with nothing better to do, when do M/G and L/100K equal each other? Or do they ever?

I may try this exercise if no one answers soon.

 

[hemihustlin]

For those with nothing better to do, when do M/G and L/100K equal each other? Or do they ever?

I may try this exercise if no one answers soon.

Somewhere right around 15 I believe

 

[TestPilot57]

NM, there's a calculator out there (big surprise, right?). Turns out that 15.3367 mpg is the same as L/100km.

MPG Converter - Fuel Economy Conversion

MPG converter lets you recalculate fuel economy units between US and Imperial miles per gallon and liters per 100 kilometers.

www.omnicalculator.com

 

[turkeybird56]

On the highway we average 19-20 with our 3.21 axle. We just completed a 2500+ mile trip pulling a TT that was about 5600 lbs as loaded. We averaged 10.3

The above is my mileage on MY 19 Bighorn. I do get about 12 mpg when towing, but I am only towing about 6,500 lbs and just a local trip for hay and such. And when towing, no push hard to accelerate, moderate gas pedal and let tranny do the work some, all IMHO..

 

[15BlueStreak]

I have a 2020 Ram with the 3.92 gears 4x4 and more aggressive falken at3w tires stock size. We drove it to NC from OH for vacay. It netted 20mpg. Not bad at all really. Around home which is a lot of short trips. It is anywhere from 12-13mpg winter. And 14-16mpg summer. Truck has 7600 miles on it.

 

[Sandevino]

I’m averaging 26mpg with mixed driving and have 4300 miles on my 2021 with 3.21’s.

 

[Bigs]

2021 Classic 5.7 with 3.92 here. This is summer driving, in winter, I know I'll need to put some cash aside for gas!

Mine is still "new" with 1900mi and I average 19mpg combined on pretty much every fill-up. Mind you I'm never stuck in traffic but I do get a lot of red lights.
I also don't gun it (as much as I would love to), I drive normal, a few good take offs here and there to hear the Magnaflow, floor to pass on the highway etc. I don't drive it like a 90yr old but I don't drive it like when I was 16 either. I also put the recommended 89 octane fuel if that ever makes a difference. (I have not tried 87 or 91)

Obviously, conditions also play a lot on your gas mileage.

 

[Farmer Fran]

My 2020 1500 Limited just got 18.1 on a 1000 miles round trip - mostly highway 75 to 79 mph... with some 55 - 45 - 35 traffic lights on the divided highway. This was with the bed cover off, all windows open (front, rear, sunroof and back window). THe truck weighed about 6700 lbs. I was in Aero mode also.

So to me 15 seems very low. 3.21 will net you a mile or two per gallon.

 

[HandyCruiser]

Our new truck has about 800 miles on it. So it's still breaking in. Current mileage is 17.5 mpg which is lower than I would like. Here's the spec's.

2021 Laramie 4x4 Crewcab 5'7" bed
5.7L V8 HEMI MDS VVT Engine (no e-Torque)
Curb Weight: 5241 lbs.
Gross Vehicle Weight Rating: 7100 lbs. / Payload: 1860 lbs.
Max. Towing: 11320 lbs. / Gross Combined Weight Rating: 17000 lbs.
8–Speed Automatic 8HP75 Transmission
1st 4.71
2nd 3.14
3rd 2.10
4th 1.67
5th 1.29
6th 1.00
7th 0.84
8th 0.67
Reverse 3.30
3.92 Rear Axle Ratio
275/55R20 OWL All–Season Tires (Circumference 100.2", Width 10.8", Height 31.9")

In 8th Gear, the engine turns once for every 3.179 feet traveled.
=1/(0.67*3.92)*(100.2/12)

With a 3.92 Rear Axle Ratio at 75 mph, engine RPM is approx. 2076.
=(75/60)*(5280/3.179)

With a 3.21 Rear Axle Ratio, the truck would travel 22.12% further at 3.883 feet traveled.
=(1/(0.67*3.21))*(100.2/12)

With a 3.21 Rear Axle Ratio 75 mph, engine RPM would be approx. 1700.
=(75/60)*(5280/3.883)

To get the same travel distance with a 3.92 Rear Axle Ratio, the tire height would need to be increased to approx. 38.9".
A set of 320/75R20 tire would get you there, but I doubt the truck would have clearance for them without modification.

 

[LSU04_08]

I have a new Limited with 3.92 gears. I pull nothing and my hwy mileage is 15mpg. Has anyone done a change to a 3.40 or 3.21 and how much did your gas mileage go up. Everytime I start it, it is at least 100 mi trip. It drinks gas like a gasaholic. It is a play pretty and may haul 200 pounds in the back every 3 months. Truck has 5300 miles.

I bought a 2021 Laramie Night Edition last Friday, it also has the 3.92 gears. The jump when I barely press the gas is a huge difference from the 2016 Ram Lonestar I traded that had 3.21 gears. I noticed that I'm pushing 2,000 RPMs at 75-80 MPH when my Lonestar was barely pushing 1,500 RPM's at that speed. I averaged 18.0 on that one but not before I had a few thousand miles on it. I'm not quite sure what I'm currently getting, but I've noticed a difference in pickup speed since my engine is getting close to 500 miles. It should get better for you (I would hope) as you put a few more miles on her. The trucks are rated for 23-25 MPG on the HWY, even with the 3.92 gears.