RAM 1500 Diesel Forum banner

1 - 20 of 21 Posts

·
Registered
Joined
·
796 Posts
Discussion Starter · #1 ·
I am seeing a lot of trucks here in the North East with 3.21 gears. Which do you have and prefer?

For the best MPGs, I assume 3.21 would do it for mostly highway use? Would it 'lug' the engine more being at a lower rpm?

Is there a noticeable acceleration difference off the line?

Thanks
 

·
Super Moderator
Joined
·
3,652 Posts
What Bounty says is true. However at a max tow for the 3.21 it often or likely would have to divide the work, accelerate the load especially up a long grade or switchback and or maintain interstate speed especially into the wind, with one less gear. Compared to how the 3.92 truck would handle the same load.

Is one gear set better than the other? Yes. If you don’t have to tow a high aerodynamic drag max load the 3.21 is better. Better highway mileage. With the exception being acceleration. The 3.92 truck will always be quicker. And well Ram generally rates the 3.92 to tow more than the same truck 3.21.

Back to the max load. Where the 3.21 truck would have to divide the work or acceleration with 5 gears and hold say 65 mph with 6 gear. The 3.92 would divide the work between 6 gears and be able to comfortably maintain 65 in the first overdrive or 7th gear.

Similarly only more exaggerated when the 2500 guys with the Hemi 6 speed had to do the above max tows they complained about the stuck high winding in a low gear to do the work. Because it didn’t have the smaller steps it needed to make and hold the next gear. When they transitioned into the eight speed with more gears to divide the work and better gear stepping the complaints stopped.
 

·
Registered
2021 Ram 1500 EcoD Laramie 4x4 crew cab ORP w/all the goodies
Joined
·
25 Posts
Had the 3.21 with the ‘17 Hemi and have the 3.92 with the ‘21 EcoD. I don’t tow that often or that heavy. This EcoD has plenty of torque and pep. Would take the 3.21 gears every day instead. Also, mpg (via Fuelly) suffers dramatically in the 3.92 over 70mph. I do long haul trips on the west coast and we are doing 75-85mph when on freeways and my gut feeling is that I’m giving up somewhere in the 3-5mpg range. On top of that the revs are pretty high. Pic from January.

C676C863-817C-4C03-A0AC-BCA7077BD3E9.jpeg
 

·
Registered
Joined
·
1,290 Posts
If you do a lot of turnpike driving get the 3:21's. My experience is the same as @RamIdaho , except I rarely drive above 65 mph. Had a 2017 hemi with 3:21's that could get 25.5 mpg on a long trip. If I were to buy a 2021 Ecodiesel, would get the 3:21 .
 

·
Registered
Joined
·
74 Posts
A question I doubt anyone here can answer. Why did they drop the 3.55 rear end. Seems like a good compromise to me. My trailer is only 6k lbs but a barn might be slightly more aerodynamic. It pulls well with the 3.55 but I wouldn’t want to do it with any higher gearing. A 3.92 would kind of suck for the other 80% if my driving.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
373 Posts
There's a reason the 3.92 is an at-cost option. It's the most preferable ratio.

Having said that, if MPG is your primary objective, the 3.21 is the way go to with the diesel. On a gas engine, the RPM range is so great that gear ratio doesn't make a lot of difference in efficiency. But on the diesel, the RPM band is really narrow and peak torque happens around 1,600 RPM. Totally different ballgame. In this scenario efficiency is VERY dependent upon RPM. And that's what we've seen via owner reports. The guys with 3.21s are swearing they see upper 20s while the guys with 3.92s are in the low 20s.

So if you bought the truck solely for MPG: 3.21

If you bought the truck to use as a truck: 3.92
 
  • Like
Reactions: justind

·
Registered
2021 Ram 2500 Tradesman Crew Cab 6.7 L Turbo Cummins 3.73
Joined
·
1,304 Posts
If you ever plan to add larger tires, 3.92 without question. I’ve got a 2nd gen eco with the GDE tune so approx same power as the 3rd gen. I’m on 35’s and the 3.92’s are a good fit, still tows well and they bump my hwy rpms down a bit.
with the 3.92, you can "adjust" the finals with tire size.
 

·
Registered
Joined
·
1,931 Posts
I wouldn't want anything but 3.92 gears, but I also do a lot of towing and mountain driving. I also don't drive very fast. Most of my speeds range between 55 mph and 70 mph. I don't drive any faster than 65 mph when towing.
 
  • Like
Reactions: sourdo and justind

·
Registered
Joined
·
796 Posts
Discussion Starter · #12 ·
Had the 3.21 with the ‘17 Hemi and have the 3.92 with the ‘21 EcoD. I don’t tow that often or that heavy. This EcoD has plenty of torque and pep. Would take the 3.21 gears every day instead. Also, mpg (via Fuelly) suffers dramatically in the 3.92 over 70mph. I do long haul trips on the west coast and we are doing 75-85mph when on freeways and my gut feeling is that I’m giving up somewhere in the 3-5mpg range. On top of that the revs are pretty high. Pic from January.
I wonder what the RPM would be with 3.21 at 85 mph
 

·
Registered
Joined
·
9 Posts
I am seeing a lot of trucks here in the North East with 3.21 gears. Which do you have and prefer?

For the best MPGs, I assume 3.21 would do it for mostly highway use? Would it 'lug' the engine more being at a lower rpm?

Is there a noticeable acceleration difference off the line?

Thanks
I am seeing a lot of trucks here in the North East with 3.21 gears. Which do you have and prefer?

For the best MPGs, I assume 3.21 would do it for mostly highway use? Would it 'lug' the engine more being at a lower rpm?

Is there a noticeable acceleration difference off the line?

Thanks
If I'm not mistaken I think the 321 gear is for two-wheel drive you couldn't put it in the four-wheel drive that should change the front and rear but I believe it's for a two-wheel drive truck only That's how they're getting 33 mi to the gallon with it
 

·
Registered
2017 Ram 1500 Tradesman commercial duty, CC, ED, 6'4"
Joined
·
54 Posts
back in the day (2017) that's why I went with the 3.55 gearing.
 

·
Registered
Joined
·
57 Posts
If I'm not mistaken I think the 321 gear is for two-wheel drive you couldn't put it in the four-wheel drive that should change the front and rear but I believe it's for a two-wheel drive truck only That's how they're getting 33 mi to the gallon with it
Negative. My son has a 2020 Crew Bighorn 4x4 with 3.21 gears.
 

·
Registered
Joined
·
1 Posts
I am seeing a lot of trucks here in the North East with 3.21 gears. Which do you have and prefer?

For the best MPGs, I assume 3.21 would do it for mostly highway use? Would it 'lug' the engine more being at a lower rpm?

Is there a noticeable acceleration difference off the line?

Thanks
I have a 2020 with the 3.92. I commute 80 miles round trip and average 28-30 mpg this time of year. I live in Michigan and most of the driving is on relatively flat roads. 11,000
Miles no issues yet.
 

·
Registered
Joined
·
373 Posts
Negative. My son has a 2020 Crew Bighorn 4x4 with 3.21 gears.
Right. ALL of these 5th Gen Rams with the new EcoDiesel come with 3.21 gears. Doesn't matter if it's 4x4 or not.

The 3.92 gears are an option you have to select on the order sheet and pay money for.


89690
 

·
Registered
Joined
·
8 Posts
I've got 3.21's in my 21 eco. I've had the truck 3 months and has 11,000 miles on it already so I wanted the better mileage. Pulling my boat is no issue (18' crestliner), and next week will be my first heavier tow with it pulling my new project Bronco home from 2 hours away. I'm curious to see how it does.
 
1 - 20 of 21 Posts
Top