2021 Ram 1500 Limited 3.92 gears change to road gears

[TestPilot57]

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.

As you said, breaking in. 17.5 is fantastic with your specs, JMO.

A '60s vehicle with the same specs wouldn't even have DREAMED of breaking 10. More like 6-7.

What are you expecting?

I really don't get people who buy a 2.5 ton truck with a V8 and expect Prius mileage.

 

[HandyCruiser]

As you said, breaking in. 17.5 is fantastic with your specs, JMO.

A '60s vehicle with the same specs wouldn't even have DREAMED of breaking 10. More like 6-7.

What are you expecting?

I really don't get people who buy a 2.5 ton truck with a V8 and expect Prius mileage.

You could likely have beat that with your old vehicle with the right camshaft, heads, intake and carb. I got my 1984 Chevy C30 1-ton up to around 10 mpg with all of that plus enough horsepower not to get embarrassed going up hills.

But it's carrying more weight than our pickup trucks. And the poor little 350 engine came stock with less horsepower than the weakest PT Cruiser engine ever made.




Overall, it's realistic to expect a little 5.7 Hemi with MDS to do better than the old stuff. Right now, it's only beating my 2003 RAM w/V8 by 1.5 miles per gallon. I don't expect Prius fuel mileage. That would be 58 mpg City/53 mpg Highway. And I don't expect fuel mileage similar to my Chevy C30 1-ton built during the very worst era at GM. What I would like is something similar to our Dodge Scat Pack 392 fuel mileage or my Charger R/T Daytona with 93 octane tune, which both average 22 mpg.

The good part is that the RAM 1500 runs on 87 octane fuel. So I'm about at the break-even point on fuel costs since both our former Scat Pack and my R/T Daytona need 93 octane fuel. Current fuel prices in my area are $2.76 for regular and $3.39 for 93 octane premium. This means I was paying a 23% upcharge for fuel for the Scat Pack. At 18 mpg burning regular fuel in the Laramie, I would be paying the same as when driving the Scat Pack, getting 22 mpg and using 93 octane fuel.

 

[TestPilot57]

A 4x4 1500 QC/CC weighs approximately 20-25% more than a Charger.

By the way, I don't use MDS. It's annoying as all get out.

And as for 60's vehicles getting better mileage with newer/better heads, cams, intake and carbs - duh. They didn't have them back then. And BTW, the '60s do not equal the '80s.

 

[bolivarshagnasty]

DON'T GIVE UP HOPE OP, I have a 21 Longhorn Limited with the same 3.92 gears. The mileage has definitely improved as I have approached 5k miles. The best run so far on 87 octane gas is 19.8 average for 300 miles or so. I do have to keep the speed between 70 to 75 mph. At 75, the rpm's are just over 2k, so it helps to keep it closer to 70. My first 4 or 5 tanks of gas averaged 13 or so. I think the computer is learning how you drive as well as the increased internal friction you have with a new engine. Just changed my oil before a trip up to Ohio, so I'm still hoping to see 20.00 mpg someday. Save your money on the differential changes and enjoy the truck!

 

[Ibsledge]

Love my Limited with its 3.92 gears. Hopefully yours go up but like som said It’s the speed. I took a recent trip. Drove 60 mph and I was low 20ish. Next tank I was averaging 70+ mph and it dropped to 16 or 17. I only have 8000 miles

 

[LSU04_08]

Love my Limited with its 3.92 gears. Hopefully yours go up but like som said It’s the speed. I took a recent trip. Drove 60 mph and I was low 20ish. Next tank I was averaging 70+ mph and it dropped to 16 or 17. I only have 8000 miles

I, too, have the 3.92 gears. I've been rolling 75+ on the interstate which is the biggest portion of my drive, and at 888 miles, I'm sitting at 19.3 MPG. Drivetrain makes a fairly big difference as well. I bought a RWD for that reason, plus I don't go off-road in my pickup.

 

[Anthony Bulger]

If you decide to switch, I have a 3.21 front diff complete I'm trying to sell. I swapped to 3.92's for bigger tires.

 

[runamuck]

I get 19-21 on the highway with mine. cruise at 75 or so. less around town because the 3.92 rear makes the truck very responsive and it's hard not to drive it like a sports car sometimes and the low first gear will cause it to eat some gas in stop and go traffic.

 

[10mmGlock]

The biggest disappointment I have had with trading my 2018 in on my 2020 was going from the 3.92 gears to the 3.21! My fuel milage has gone to crap, the truck works way harder to get moving around town and searches for gears on the highway, get a good intake and exhaust and bed cover and you should pull around 20 on the hwy, at least that's what mine was getting.

 

[TestPilot57]

The biggest disappointment I have had with trading my 2018 in on my 2020 was going from the 3.92 gears to the 3.21! My fuel milage has gone to crap, the truck works way harder to get moving around town and searches for gears on the highway, get a good intake and exhaust and bed cover and you should pull around 20 on the hwy, at least that's what mine was getting.

Maybe you should change your name to 9mmGlock.

 

[10mmGlock]

Maybe you should change your name to 9mmGlock.

Haha, what size are your tires and what suspension mods did you do?

 

[TestPilot57]

Haha, what size are your tires and what suspension mods did you do?

Currently I have General ATXs 35x12.50-20s with a 2" front level via adjustable links on my 4C air suspension.

Last night I dropped my truck off to a local shop to install my 5" Rough Country lift. I expect/plan to dial it down a bit via my adjustable links (to make it more garage-friendly). My main purpose is to avoid rubbing on the turns in the front fender area. I had hoped/expected that a 2" front lift via links would do it, but no avail.

 

[TestPilot57]

Oh, and I have 1/2" spacers to clearance the front tires.

 

[10mmGlock]

Damn I bought the 2.5 level kit and was going to try and find 1" spacers as I wanted to run the same size, I may have to go 285/60/20 which I believe equates to about a 34

 

[stormcom]

Well, I am still driving it. Filled up with ethanol free fuel and it bumped up to almost 17. I will just keep driving it. BTW, has anyone had seat foam issues. I am over 6ft. and it seems I am falling thru the back of the seat after 150 mi. Still like the truck.