3:21 rear vs 3:92 gas mileage?

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

ramffml

Senior Member
Joined
Jul 12, 2019
Posts
2,808
Reaction score
5,134
Location
ramforum
Ram Year
2019
Engine
hemi 5.7
Well that's the first person I've ever heard complain about a deeper ratio other than a fleet account manager.

Your confirmation bias is extremely visible in this thread. "That's the first person", "Nobody ever regrets" and so on. You should really read the forum for a bit before forming those opinions, gas mileage comes up time and time again (read the title of this thread).

But all that aside, people can buy what they want. I won't try to convince someone not to buy the 3.92 if that's what they want and they have the facts. I just get annoyed when people misrepresent the 3.21 as if the 3.92 is going to save them from a world of hurt and automatically transform their beast of burden into a cummins killer.
 

pacofortacos

Senior Member
Joined
Apr 18, 2017
Posts
3,565
Reaction score
4,342
Ram Year
2016
Engine
5.7
Only time I hit 74mph is when I'm passing. :D Speed limit here is 60 mph or lower.
Haha, mostly 45-55 here, but I pretty much only use the truck for vacations and thus interstate speeds.

I spec 74 mph, because it seems that I can watch the gas gauge drop faster at speeds above that mph.
It seems like I'm sinning when going out west and the speed limit is 75 mph and I'm going 74 mph - if there's a wind I have seen as low as 12.5 mpg and that isn't towing. Ouch
 

pacofortacos

Senior Member
Joined
Apr 18, 2017
Posts
3,565
Reaction score
4,342
Ram Year
2016
Engine
5.7
The effect on engine life is negligible in the sense of what we're talking about. Engine life is largely simplified down to the total amount of fuel sent through it and today's engines nearly always outlast any pickup truck they're put in. The reduced torque on the stuff behind the engine will generally help all that stuff live longer. Traveling down the road is a work equation and more rpm = less torque = happier parts.
That last part isn't true for a gas engine, they make much more torque in the higher rpms and as said significantly more heat in the rear end. At 70 mph, the 3.21 in 8th is around 1500 rpm or less, the 3.92 is almost touching 2000 rpms. Empty, I am out of first gear by about 3-4 mph normally, so it's almost useless.
Nice chart!! I'm gonna ask a question and I'm not trying to be argumentative...just trying to learn. If the ram's are basically the same at 65 mph, will they still be the same at 70, or 75 mph?? If you stayed locked in that gear...or would the 3.92 be at a higher rpm as speed goes up compared to the 3.21?? If they stay the same I can't see a major difference in the gearing, if the 3.92 gears would have higher rpm than the 3.21 at 70, or 75...then I would think the 3.92 would be the better option for towing, but probably not so much for gas mileage.
Once both are in 8th gear is when the differences show at higher speeds.
IMO the 3.92's shine in rural country driving, I am in 8th gear at about 43 mph and it's very comfortable and fun to drive in the 45 - 55 mph zones - where as the 3.21's will tend to search between 7th and 8th at those speeds.
 

KKBB

Senior Member
Joined
Apr 4, 2021
Posts
618
Reaction score
830
Location
Oakland Ia
Ram Year
2019
Engine
6.4
That last part isn't true for a gas engine, they make much more torque in the higher rpms and as said significantly more heat in the rear end. At 70 mph, the 3.21 in 8th is around 1500 rpm or less, the 3.92 is almost touching 2000 rpms. Empty, I am out of first gear by about 3-4 mph normally, so it's almost useless.

Once both are in 8th gear is when the differences show at higher speeds.
IMO the 3.92's shine in rural country driving, I am in 8th gear at about 43 mph and it's very comfortable and fun to drive in the 45 - 55 mph zones - where as the 3.21's will tend to search between 7th and 8th at those speeds.
We just got my wife a used 2022 limited 1500 a month or so ago. It has the 3.21, and so far I like it. I get what you are saying. We have a 6 mile stretch that is a 55 mph zone and we drive around 60. That stretch is flat as can be and it is great on that. The next 6 miles is hilly and it downshifts on every hill. They are pretty good hills, but not long at all and then back downhill. I'm sure the 3.92 would be better on that stretch, but I still think it would downshift also. I'm used to the Cummins that would basically never downshift, even pulling a good sized 5th wheel. My truck is a 2019 2500 with the 6.4 and 3.73. I love the truck, bit still after exactly 4 years with that truck I'm still not used to it downshifting on every small hill while empty. It is fine because the 8 speed is so smooth you can't tell it downshifted unless you look at the rpm's. I actually went and test drove a cummins the other day, but the cost and the fact they haven't done any changes from 2019 to 2024 model year made it an easy decision to stay with what I have.
 

pacofortacos

Senior Member
Joined
Apr 18, 2017
Posts
3,565
Reaction score
4,342
Ram Year
2016
Engine
5.7
We just got my wife a used 2022 limited 1500 a month or so ago. It has the 3.21, and so far I like it. I get what you are saying. We have a 6 mile stretch that is a 55 mph zone and we drive around 60. That stretch is flat as can be and it is great on that. The next 6 miles is hilly and it downshifts on every hill. They are pretty good hills, but not long at all and then back downhill. I'm sure the 3.92 would be better on that stretch, but I still think it would downshift also. I'm used to the Cummins that would basically never downshift, even pulling a good sized 5th wheel. My truck is a 2019 2500 with the 6.4 and 3.73. I love the truck, bit still after exactly 4 years with that truck I'm still not used to it downshifting on every small hill while empty. It is fine because the 8 speed is so smooth you can't tell it downshifted unless you look at the rpm's. I actually went and test drove a cummins the other day, but the cost and the fact they haven't done any changes from 2019 to 2024 model year made it an easy decision to stay with what I have.
On mine with the 3.92's, it also downshifts at the slightest hill when using cruise, it's not as bad using the foot but i would prefer for it to bog just a bit instead of the quick downshift.

In the Florida keys, on cruise and doing 45-55 mph (45 zone with a lot of police), I can pull 28-30 mpg with MDS on and in 8th gear. It'll drive in 4 cyl. mode for miles on end down there and in 8th gear.
 

Wild one

Senior Member
Joined
Jan 17, 2016
Posts
13,896
Reaction score
23,817
Ram Year
14 Sport
Engine
5.7
On mine with the 3.92's, it also downshifts at the slightest hill when using cruise, it's not as bad using the foot but i would prefer for it to bog just a bit instead of the quick downshift.

In the Florida keys, on cruise and doing 45-55 mph (45 zone with a lot of police), I can pull 28-30 mpg with MDS on and in 8th gear. It'll drive in 4 cyl. mode for miles on end down there and in 8th gear.
The 8 speed uses differant shift parameters when cruise is enabled . It'll hunt gears more in cruise mode,then it will if you're using the skinny pedal and manually maintaining speed . Alot of guys think cruise is the way to go to get their best milege,when it's not , you'll get better milege by actually driving the truck yourself. That of course assumes you know how to drive for milege , if you don't, then cruise might be your better option.
I can pull down 30+ mpg in the wifes Challenger when i'm driving it,if i let cruise drive it,it's lucky if it gets 28 mpg.
 

Attachments

  • IMG_2268.JPG
    IMG_2268.JPG
    108.9 KB · Views: 4
  • IMG_2267.JPG
    IMG_2267.JPG
    115.8 KB · Views: 3
  • IMG_4051 (2).JPG
    IMG_4051 (2).JPG
    108.8 KB · Views: 3

marine0311

Senior Member
Military
Joined
Feb 20, 2024
Posts
143
Reaction score
287
Location
Ohio
Ram Year
2015
Engine
5.7 Hemi
For me the 3.92 will work best as I have plenty of gear to haul around. My mileage suffers with the extra weight. And of course the loose nut behind the steering wheel enjoying his Hemi will ultimately determine mileage
 

pacofortacos

Senior Member
Joined
Apr 18, 2017
Posts
3,565
Reaction score
4,342
Ram Year
2016
Engine
5.7
The 8 speed uses differant shift parameters when cruise is enabled . It'll hunt gears more in cruise mode,then it will if you're using the skinny pedal and manually maintaining speed . Alot of guys think cruise is the way to go to get their best milege,when it's not , you'll get better milege by actually driving the truck yourself. That of course assumes you know how to drive for milege , if you don't, then cruise might be your better option.
I can pull down 30+ mpg in the wifes Challenger when i'm driving it,if i let cruise drive it,it's lucky if it gets 28 mpg.
I agree. Since most of my mileage is long highway trips, I can't not use cruise! haha

Part of the problem is with it wanting to exactly keep the speed it's set at. I wouldn't mind a drop of 1-2 mph on an incline to prevent a downshift, esp. on going over a highway overpass.
On my 01 Dakota w/the 5.9, I installed a cable throttle stop on the cruise cable so that it couldn't downshift - don't have that ability on the Ram with fly by wire :)

It's really one of the few gripes I have about my Ram and it isn't really a problem with the truck, it 's just what I like. If only that was an adjustable parameter!

I've never driven a 3.21 equipped Ram, so I don't know if it downshifts as quickly or not. It almost feels like my truck has a bit more power at 1400 rpm than at 2000 rpms (light throttle). Feels a bit flat from 1800-2000 rpms, good power below that and above 2200 rpms. All doing a bit of lugging of the engine using the pedal. I'm sure it's all in the programming as it is stock programming and most of my driving is in the 1800-2000 rpm range through all the gears (until 8th gear) during light throttle driving.
 

pacofortacos

Senior Member
Joined
Apr 18, 2017
Posts
3,565
Reaction score
4,342
Ram Year
2016
Engine
5.7
The 8 speed uses differant shift parameters when cruise is enabled . It'll hunt gears more in cruise mode,then it will if you're using the skinny pedal and manually maintaining speed . Alot of guys think cruise is the way to go to get their best milege,when it's not , you'll get better milege by actually driving the truck yourself. That of course assumes you know how to drive for milege , if you don't, then cruise might be your better option.
I can pull down 30+ mpg in the wifes Challenger when i'm driving it,if i let cruise drive it,it's lucky if it gets 28 mpg.
Now if we can only get the Ram's to do that kind of mileage :)
 

Wild one

Senior Member
Joined
Jan 17, 2016
Posts
13,896
Reaction score
23,817
Ram Year
14 Sport
Engine
5.7
I agree. Since most of my mileage is long highway trips, I can't not use cruise! haha

Part of the problem is with it wanting to exactly keep the speed it's set at. I wouldn't mind a drop of 1-2 mph on an incline to prevent a downshift, esp. on going over a highway overpass.
On my 01 Dakota w/the 5.9, I installed a cable throttle stop on the cruise cable so that it couldn't downshift - don't have that ability on the Ram with fly by wire :)

It's really one of the few gripes I have about my Ram and it isn't really a problem with the truck, it 's just what I like. If only that was an adjustable parameter!

I've never driven a 3.21 equipped Ram, so I don't know if it downshifts as quickly or not. It almost feels like my truck has a bit more power at 1400 rpm than at 2000 rpms (light throttle). Feels a bit flat from 1800-2000 rpms, good power below that and above 2200 rpms. All doing a bit of lugging of the engine using the pedal. I'm sure it's all in the programming as it is stock programming and most of my driving is in the 1800-2000 rpm range through all the gears (until 8th gear) during light throttle driving.
You can still use cruise,but if you're approaching a grade that you think it'll downshift on,just slightly over ride the cruise by stepping on the gas pedal. After awhile you should be able to tell by the feel of the pedal how far you can over ride the cruise with-out it shifting down. It's a fine line,but with some time and practice,you can usually learn the feel of the pedal. Everything you knew about cable systems,you have to forget though,lol .I miss the pedal feel a cable gave you,but you can learn the drive by wire system to with a bit of practice
 

pacofortacos

Senior Member
Joined
Apr 18, 2017
Posts
3,565
Reaction score
4,342
Ram Year
2016
Engine
5.7
You can still use cruise,but if you're approaching a grade that you think it'll downshift on,just slightly over ride the cruise by stepping on the gas pedal. After awhile you should be able to tell by the feel of the pedal how far you can over ride the cruise with-out it shifting down. It's a fine line,but with some time and practice,you can usually learn the feel of the pedal. Everything you knew about cable systems,you have to forget though,lol .I miss the pedal feel a cable gave you,but you can learn the drive by wire system to with a bit of practice
I've gone to the foot on pedal, pause cruise, crest overpass, reengage cruise - this is usually when towing the boat.

At least it is 100 times better than my Pacifica was, it used to drop speed a couple of mph, downshift 1 or 2 gears, then fly over the crest of the hill and go 10+ mph over the set speed, then coast, then downshift 2-3 gears to slow down lol. It was the worst cruise control, I have ever used.

I wish the Ram +/- worked like my wife's mazda 3 manual mode automatic. On it when I go manual, it locks that gear in and won't downshift until you are really bogging the engine and have lost several mph and rpms - with cruise on or even using the foot - then it will downshift.
So it pretty much limits up and downshifting until you have gone to the extreme ends of the set gear range. (At least I think it will upshift if you get near redline, but haven't tried it.)
 

Wild one

Senior Member
Joined
Jan 17, 2016
Posts
13,896
Reaction score
23,817
Ram Year
14 Sport
Engine
5.7
I've gone to the foot on pedal, pause cruise, crest overpass, reengage cruise - this is usually when towing the boat.

At least it is 100 times better than my Pacifica was, it used to drop speed a couple of mph, downshift 1 or 2 gears, then fly over the crest of the hill and go 10+ mph over the set speed, then coast, then downshift 2-3 gears to slow down lol. It was the worst cruise control, I have ever used.

I wish the Ram +/- worked like my wife's mazda 3 manual mode automatic. On it when I go manual, it locks that gear in and won't downshift until you are really bogging the engine and have lost several mph and rpms - with cruise on or even using the foot - then it will downshift.
So it pretty much limits up and downshifting until you have gone to the extreme ends of the set gear range. (At least I think it will upshift if you get near redline, but haven't tried it.)
I have a 1 ton GM as a work vehicle,there's times i think i should shoot it,because of the cruise,lol. It has the worst cruise i've ever had,and sounds alot your Pacifica. It made it to 60,000 miles before the oil pump died ,and took the engine out,i was hoping i'd get a new one,but no the bean counters decided dropping a new engine in it was a better idea.
 

Aircommuter

Member
Joined
Nov 28, 2021
Posts
48
Reaction score
67
Location
Coulterville
Ram Year
2019
Engine
Hemi 5.7
The 8 speed locks the convertor in every gear,so that argument is a moot point.It's not like the old days where a convertor only locked in high gear. Once your rolling and past 1st gear with 3.92's,the 3.21's still in first gear have the torque advantage,and in the upper gears,the computor will put both trucks in the engines rpm sweet spot,not the transmission or convertors sweet spot,they'll both be rolling down the road at the same rpm while towing,until you hit 8th
Can lock the converter in every gear but only does so depending on throttle position. Otherwise no point in having a torque converter.
 

RodRamCar

Senior Member
Military
Joined
Jul 7, 2022
Posts
320
Reaction score
409
Location
IdaHO
Ram Year
2022 Longhorn
Engine
5.7 4x4 w/ 3.92s
The 3.92s are the only way!!!! haha. Like others have said, unless you're going to be towing a heavy trailer around all the time, get either won't matter. Now if you're towing anything 7k or more all the freaking time, and you can pony up the pennies, just get a dang Cummins. I have so many hills i'd likely never buy another 1500 again if I could manage to get a 2500 6.7L without selling my kidney to afford it.
 

Aircommuter

Member
Joined
Nov 28, 2021
Posts
48
Reaction score
67
Location
Coulterville
Ram Year
2019
Engine
Hemi 5.7
A 3.21 WILL select the same RPMs that the 3.92 does.

Look at the calculated chart below. When the 3.92 is in 7th gear at 65 mph, it's RPMs (blue cell) are 2194. Now look at the 3.21 columns, the various gears at 65 mph are:

5th/green: 2870
6th/blue: 2191
7th/purple: 1796.

Which gear do you think the 3.21 will be in? Obviously 6th/blue @ 2191, which is exactly 3 rpms less than the 3.92

When your RPMs are "equivalent" and your MPH are equivalent, then so is the torque to the wheels.

View attachment 537857
Blue is the only match in the chart. First and second are the most important for towing because it is when the torque is needed to get the vehicle moving. I have changed final drive gear ratios in dozens of customers trucks in the last fifty years in my shop and it makes a difference. The ratios all have their purpose.
 

BILL JAMISON

Junior Member
Joined
Jun 3, 2021
Posts
15
Reaction score
15
Location
Harrisburg, Pennsylvania
Ram Year
2022 Ram Rebel Black Crystal Pearlcoat
Engine
5.7 Hemi
I've had two 5th gen Rams, both hemi. The Big Horn had 3.21 and my Rebel has 3.92. There is a significant difference in the mileage between the two. On a trip, the Big Horn would get 20-22 mpg at highway speeds. The Rebel, with the 3.92, at best, gets 18.5 mpg on average. So in my experience, there is a difference between the two of them.
2022 Rebel, Hemi, loaded, Black Crystal Pearlcoat.
 

ramffml

Senior Member
Joined
Jul 12, 2019
Posts
2,808
Reaction score
5,134
Location
ramforum
Ram Year
2019
Engine
hemi 5.7
Blue is the only match in the chart. First and second are the most important for towing because it is when the torque is needed to get the vehicle moving. I have changed final drive gear ratios in dozens of customers trucks in the last fifty years in my shop and it makes a difference. The ratios all have their purpose.

No, the other colors also match close enough; and you'll note that for the majority of the time those 2 trucks are in those equivalent colored gear ratios it's the 3.21 that has a tiny edge with a higher gear ratio giving slightly higher RPMs and more power.
 
Top