RAM 1500 Diesel Forum banner
21 - 40 of 78 Posts

·
Premium Member
Joined
·
5,250 Posts
A question I doubt anyone here can answer. Why did they drop the 3.55 rear end.
My guess is they realized how close together 3.55 and 3.92 actually are in real-world use. Switching to 3.21 and 3.92 actually gives buyers better choices based on how they want to use their truck. Going to 3.21 probably gave them better mpg numbers as well.

There's a reason the 3.92 is an at-cost option. It's the most preferable ratio.
I would argue that it's not the most preferable. I had my truck built, optioned it out very well, and knew I would be using it to tow heavy and frequently. 3.55 work very well for me at the truck's max tow rating or slightly above.
 

·
Registered
2021 Ram 1500 Limited EcoDiesel
Joined
·
5 Posts
The window sticker on mine says 32mpg, it has 3.21 and is 2 wheel drive. It was the only one available in the state when I bought it. Every other truck had 3.92 and 4 wheel drive and said 29mpg.
 

·
Registered
2019 RAM 1500 Tradesman 4X2 EcoDiesel
Joined
·
255 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?
I did calculations with the ratios for the 8HP70 tranny (Gen 2 engines), but I think they are similar for the newer model. In the upper gears, 3.21s run one gear lower to get almost identical RPMs to 3.92s. 6th gear with 3.21s is about the same as 7th gear with 3.92s and so on. In lower gears, there is a bigger difference because the ratios are spread more, but we don't spend as much time in the lower gears. With 3.21s, you would spend a little more time in 1st gear, etc. Does anyone here have experience where they had difficulty getting a trailer moving with 3.21s?

Being indecisive, I've got 3.55s, almost exactly halfway between. Under some situations, I would be in the same gear as the 3.92s, but with 10% lower RPMs. Under other situations, I might have to go down a gear, and be at 10% higher RPMs than with 3.21s. I tow about 5,000# in the upper 50s/lower 60s MPH, and I have been satisfied with how it pulls. I'm glad I don't have the 3.92s, based on the better MPGs.
Ratios.jpg
 

·
Registered
Joined
·
368 Posts
One also needs to consider the tire size, there is a difference in rotational height between the 17s and 20s.
 

·
Registered
Joined
·
1,176 Posts
I had a '15 with 3.55 and now the '20 with 3.92. I tow a 7+k camper a lot and the 3.92 is definitely better especially when you're maneuvering and backing up at slow speeds on uneven ground. In those situations I was constantly on and off the pedal with the '15 but now it is smooth. Overall the performance feels better. I'm happy I got it.
 

·
Registered
Joined
·
1,333 Posts
I couldn't find a sticky, as I didn't know which forum to check. It could be this one, but it doesn't include many data.
3.21 and 3.92 Rear Gear Ratio Now Available | RAM 1500 Diesel Forum
Found it…

 

·
Registered
2021 Ram Eco Diesel Laramie Crew Cab 4x4
Joined
·
45 Posts
If you use the ram tow guide (at least for 21’s) it shows 1700 lbs less of tow capacity with the 3.21’s. The number they show for tow capacity is 7780 or 9480 with 3.92. Not sure which model this is as it’s using the same numbers for each model but the numbers look to reflect a fairly loaded model.

This is why 3.92’s are best if you’re going to end up towing towards those upper limits. Last time I checked these Max tow numbers only include a small child (most haven’t weighed 150lbs since high school) driving and a full tank of fuel. So our family, chunky butts and big gulps.take away from that. Plus all the other added items loose or aftermarket, big tires, sweet fender flares, dirty undies, etc. If you’re not going to get close to the 3.21’s Max tow numbers, go ahead and save that fuel. Otherwise get the big boy gears and make it a proper tow truck so you can bring all the clean under garments you want!
 

·
Registered
2021 Ram Eco Diesel Laramie Crew Cab 4x4
Joined
·
45 Posts
I had a '15 with 3.55 and now the '20 with 3.92. I tow a 7+k camper a lot and the 3.92 is definitely better especially when you're maneuvering and backing up at slow speeds on uneven ground. In those situations I was constantly on and off the pedal with the '15 but now it is smooth. Overall the performance feels better. I'm happy I got it.
Definitely a good point. Just to get started you can here these trucks working it. I go several miles in on mountain Forrest roads.There’s lots of slow maneuvering that gets the truck working pretty hard in forward and reverse.
 

·
Registered
Joined
·
60 Posts
I went with the 3.21's as I rarely tow anything heavier than 5000# and 90% of the time I am running down the road solo.

When I do go far, I tow a pop-up trailer with my wife, dog and rifles on the way out. The way back, it's the same and two deer if I'm lucky.

3.92's were an up-tick and something I can add later if needed. However, if I am going to go through the problem of swapping gear sets, I'll swap in 4.10's and call it a day.
 

·
Super Moderator
Joined
·
3,730 Posts
Pretty expensive aftermarket upgrade both parts & labor for 4x4. Might be as cheap to trade trucks
 

·
Registered
2021 Ram Eco Diesel Laramie Crew Cab 4x4
Joined
·
45 Posts
I went with the 3.21's as I rarely tow anything heavier than 5000# and 90% of the time I am running down the road solo.

When I do go far, I tow a pop-up trailer with my wife, dog and rifles on the way out. The way back, it's the same and two deer if I'm lucky.

3.92's were an up-tick and something I can add later if needed. However, if I am going to go through the problem of swapping gear sets, I'll swap in 4.10's and call it a day.
The 3.92’s should be plenty unless you want to run monster tires too. Aftermarket gears in Rams are known to be noisy. I know from experience a couple times there. Like Vern says the swaps can be pricey.

I think you’re in a good zone for the 3.21’s anyways. I most likely would have stuck with 3.21’s if I was using it just as you are.
 

·
Registered
2019 RAM 1500 Tradesman 4X2 EcoDiesel
Joined
·
255 Posts
I had a '15 with 3.55 and now the '20 with 3.92. I tow a 7+k camper a lot and the 3.92 is definitely better especially when you're maneuvering and backing up at slow speeds on uneven ground. In those situations I was constantly on and off the pedal with the '15 but now it is smooth. Overall the performance feels better. I'm happy I got it.
I find my Classic isn't very smooth at creeping (3.55s) and wish I had low range for lining up the hitch, etc. It seems like the throttle mechanism is a little sticky at tiny inputs. Could it be that your '20 just does that better? Also, I wonder if the lower gear ratios could have changed.
 

·
Premium Member
Joined
·
2,124 Posts
With the GDE EPA Compliant Tune. the 3.55 gears aren't too bad for my loads. It's gutless on the mountain passes, but the EcoDiesel seems to hold up well. I'll have some towing pictures in a few weeks of my 2020 (3.92 gears) towing the same trailer.

 
  • Like
Reactions: RamIdaho

·
Registered
2019 RAM 1500 Tradesman 4X2 EcoDiesel
Joined
·
255 Posts
Found it…

Thanks. He uses the same rationale as I do, but he's talking about gassers (and uses "higher" when he means "lower").
"From the speed 58-70 MPH, 3.92 has higher final drive ratio over 3.21 (8.23 vs 6.74) until it has to shift to 4th gear at 70 MPH." "Calculated towing shift point to be 6000 rpm...."

He concludes that the gasser may never be able to get up a hill at highway speeds with 3..21s, and I don't think that applies to EDs. With my 3.55s, I have pulled 5,000# up some pretty steep grades and find that the speed tends to creep up if I am trying to go 55 MPH. I think the gasser is going to be one (or two?) gears lower, where the comparable ratios are not available between the two final ratios.

Of course, I have to conclude that 3.55s win the 3.21 vs 3.92 battle!!! (Need I say LOL?)
 

·
Registered
Joined
·
1,176 Posts
I find my Classic isn't very smooth at creeping (3.55s) and wish I had low range for lining up the hitch, etc. It seems like the throttle mechanism is a little sticky at tiny inputs. Could it be that your '20 just does that better? Also, I wonder if the lower gear ratios could have changed.
My Gen 3 with 3.92 feels peppier, smoother and gets better mileage than my '15.
 
  • Like
Reactions: SlowRoller

·
Premium Member
Joined
·
5,250 Posts
Thanks. He uses the same rationale as I do, (and uses "higher" when he means "lower").
"From the speed 58-70 MPH, 3.92 has higher final drive ratio over 3.21 (8.23 vs 6.74) until it has to shift to 4th gear at 70 MPH." "Calculated towing shift point to be 6000 rpm...."
You would think a self-proclaimed 'Engineer' would know better. One of my pet peeves as well.
 

·
Registered
Joined
·
533 Posts
Definitely like my 3.92 especially with the E-Rated tires which added some unsprung weight to move. I have a 2018 and the Gen 2 runs out of steam quick on hills so every gear matters it seems.
 

·
Registered
2021 Ram 1500 EcoD Laramie 4x4 crew cab ORP w/all the goodies
Joined
·
28 Posts
Found it…

Very informative link. Thanks Henfield.
 
  • Like
Reactions: Henfield
21 - 40 of 78 Posts
Top