An Engineer's Ultimate Guide To 3.21 VS 3.92 Axle Ratio

[TAJ45]

Gee, truly amazing how the final ratio tranny drive numbers are the same as the rear gear's.....wink.

 

[TAJ45]

Nice mileage for that much city.

And How!

 

[c3k]

Lolz...great stuff.

Now, looking for real-world reports of the EcoDiesel with 3.21 and larger tires, like 34" or 35" and how the transmission works at highway speeds. Does it hunt 7-8-7-8? Or, does it comfortably shift into, and stay in, 8th gear at highway speeds with an ecodiesel and larger tires?

(Between the ZF's lower 1st gear and the ecodiesel torque, and my light towing use, I don't see a need for 3.92 grunt at the low end. But, I do see how a 3.92 would be more stable at higher speeds. Just looking for owner reports.)

Thanks.

 

[Rossum]

Now, looking for real-world reports of the EcoDiesel with 3.21 and larger tires, like 34" or 35" and how the transmission works at highway speeds. Does it hunt 7-8-7-8? Or, does it comfortably shift into, and stay in, 8th gear at highway speeds with an ecodiesel and larger tires?

I do not have larger tires, but I do have a 2021 EcoDiesel with 3.21 gears. The most annoying characteristic of this truck to me is that there's no way to lock it into a gear. My previous long-haul vehicle was a VW Touareg TDI, also a 3.0 V6 diesel with an 8 speed (Aisin) transmission. As soon as I got up to highway speed, I would move the shifter over to the right into manual mode, which would keep it in 8th gear. The RAM does downshift out of 8th more than I'd like, particularly with the adaptive cruise on. I wouldn't exactly call it "hunting". It downshifts to get back up to speed quickly, and it sometimes does so on hills, but I think it does so unnecessarily. With 480 ft-lb of torque at 1600 rpm, it really shouldn't have to do that.

If I were planning on 34" or 35" tires, I would not choose the 3.21 gears.

 

[nc_beagle]

Hi all. I registered just for this discussion and have read every message. Thanks to the OP for the explanation that kicked off this thread.

I'm trying to decide between two 2021 EcoDiesel Rams. One's a Laramie, very well equipped, with the 3.21 and one is a Rebel, modestly equipped, with the 3.92. The prices look to be similar here at the end of the year. Payloads are about the same. The Rebel is rated to tow about 9,750# and the Laramie about 8,150#. We'll be towing a travel trailer with a max weight of 6,200#. We're in the NC foothills, but plan to take it all over the country over the next several years.

Anyone have experience with this particular scenario? This would not be a daily driver, but when not used for truck stuff near home it would be for longer trips with and without the camper. I see a lot of people wanting the 3.92 for passing, etc... but I've never had an issue being able to pass someone in almost any vehicle. My daily driver is a 150hp Mazda 3 and I can get around people fine. It's a lot lighter than a truck, of course, but gives up a lot of power as well...

Anyway, I'm curious what to expect when towing the camper, particularly from a standstill. I've got to think that the torque of the diesel would help the 3.21 pull sufficiently off the line?

I'm leaning toward, but not yet sold on, the Laramie only because I don't think we will do the sort of off-roading that the Rebel might be better for, it has some of the safety features that would make me feel better when my wife is driving, and I do like getting good mileage.

Thanks for any guidance you can offer!

 

[BowDown]

Hi all. I registered just for this discussion and have read every message. Thanks to the OP for the explanation that kicked off this thread.

I'm trying to decide between two 2021 EcoDiesel Rams. One's a Laramie, very well equipped, with the 3.21 and one is a Rebel, modestly equipped, with the 3.92. The prices look to be similar here at the end of the year. Payloads are about the same. The Rebel is rated to tow about 9,750# and the Laramie about 8,150#. We'll be towing a travel trailer with a max weight of 6,200#. We're in the NC foothills, but plan to take it all over the country over the next several years.

Anyone have experience with this particular scenario? This would not be a daily driver, but when not used for truck stuff near home it would be for longer trips with and without the camper. I see a lot of people wanting the 3.92 for passing, etc... but I've never had an issue being able to pass someone in almost any vehicle. My daily driver is a 150hp Mazda 3 and I can get around people fine. It's a lot lighter than a truck, of course, but gives up a lot of power as well...

Anyway, I'm curious what to expect when towing the camper, particularly from a standstill. I've got to think that the torque of the diesel would help the 3.21 pull sufficiently off the line?

I'm leaning toward, but not yet sold on, the Laramie only because I don't think we will do the sort of off-roading that the Rebel might be better for, it has some of the safety features that would make me feel better when my wife is driving, and I do like getting good mileage.

Thanks for any guidance you can offer!

IMO, the EcoDiesel and the 3:21's would be fine. If you can, test drive them both and see how you like each but with all the low speed (rpm) the diesel provides, I cant see the 3:21 being a bad choice

 

[rbundy84]

Potential owner question - I am eyeing up a few options in my area and the new Laramie 1500s I’m looking at have 3.92 ratio. I live near St Louis (relatively flat) and wont be hauling/towing much. Should I hold out for a 3.21 or will the difference between the 3.92 be negligible in my situation (gas mileage/handling/etc)?

 

[Royalist_Ram]

Potential owner question - I am eyeing up a few options in my area and the new Laramie 1500s I’m looking at have 3.92 ratio. I live near St Louis (relatively flat) and wont be hauling/towing much. Should I hold out for a 3.21 or will the difference between the 3.92 be negligible in my situation (gas mileage/handling/etc)?

3.92 means better acceleration as well not just better towing capability. However it means lower mpg efficiency (anywhere from like 1-4 mpg’s I think, depending on what engine you get. I was gonna get the 3.21 in my ordered ‘21 Limited EcoDiesel but I went with the 3.92 because at the time the Off-Road Group required it, glad I got it really for that slightly better acceleration (supposedly).

 

[brettguercio]

traded in my 19 3.92 in on a 21 3.21 already noticing a improvement on mpg and a lot lower rpms on highway

 

[Limitedrider]

traded in my 19 3.92 in on a 21 3.21 already noticing a improvement on mpg and a lot lower rpms on highway

Do you really feel a difference in the performance?

 

[Florida Ranger]

I have a 2020 Laramie 5.7 ,,4x4 , 3.92 gears city mpg 13.2 Hwy mpg 75 mph 17.8 - 18.3.. Hwy 65 mph is 19.4 - 20.2 ,,plus truck only has 2,200 miles so far . Hopefully when it gets 4,000 miles it will get better.

 

[kenthelawnguy]

I had 3.21 gears in my 2017 limited 1500, 3.92 in my 2019 limited 1500 and I got the 3.21 in my 2021 Ram limited 1500. Why you may ask did I go back to the 3.21 gears? One thing I noticed after going to the 3.92 ratio was even though you get a little bit more of a kick off the line with the 3.92 and I mean just a little, you can really feel the pull of the 3.21 when you kick it down vs my 3.92 I had especially when kicking it down from higher speeds. I don't know if it was due to ratio diff and the 3.21 finding a better gear when kicking it down or what but to me the 3.21 seems stronger once off the line and is more fun to drive. The truck feels lighter and smoother with the 3.21 and my wife even said the same thing and she could care less about trucks. Just my 2 cents on my personal experience. Both gears tow well enough for what I would tow. If I needed to tow anything heavier I would step up to a 2500 Ram. The fuel economy is not that great of a difference so far between both gears with only 2000 miles on my new truck but let me tell you, the 33 gal tank is a must no matter which gears you go with!! High 500 to low 600 miles on highway to a tank is awesome!!

 

[Pallman]

Any idea on what the gas mileage difference is between a 3.21 and a 3.92?

Its the square of your right foot BIG TOE, to most truck owners.

 

[kenthelawnguy]

Its the square of your right foot BIG TOE, to most truck owners.

with me it has been 1-2 mpg difference on mix driving but mostly highway

 

[brettguercio]

Do you really feel a difference in the performance?

No i Feel it’s the exact same

 

[Niel McCauley]

Just spent a month driving a '20 Laramie with 3.21 axle and now have a '19 Limited with 3.92. It might be partly the extra weight, wheel size, suspension, etc but the 3.21 actually felt like the more sporty of the two. More tempting to goose a little going up hills and onto the highway., just purrs and goes.

 

[kenthelawnguy]

Just spent a month driving a '20 Laramie with 3.21 axle and now have a '19 Limited with 3.92. It might be partly the extra weight, wheel size, suspension, etc but the 3.21 actually felt like the more sporty of the two. More tempting to goose a little going up hills and onto the highway., just purrs and goes.

my same opinion after owning both axles. The 3.21 definitely feels sportier to me as well. This is why I went back to 3.21 in my 2021

Just spent a month driving a '20 Laramie with 3.21 axle and now have a '19 Limited with 3.92. It might be partly the extra weight, wheel size, suspension, etc but the 3.21 actually felt like the more sporty of the two. More tempting to goose a little going up hills and onto the highway., just purrs and goes.

 

[c3k]

I'm headed to a dealer today to do a test drive or two (or three. ). I don't expect a light truck (no tow, no load) to show much difference, but I'll see if I can find one.

My use would be an ecodiesel with occasional light utility towing. (My trailer weighs about 1100# empty, max load has been ~5000#.) With the natural low-end diesel torque and that light towing use, I'm already leaning towards the 3.21.

Light 4x4 duty, so ORP, e-locker rear.

I plan on a 2-3" lift and some larger tires, at most 34".

I really can't see a need for the 3.92 for my use/engine.

Is my inexperience causing me to overlook something?

 

[Rossum]

Is my inexperience causing me to overlook something?

I have a '21 ED with 3.21. I'm glad I chose it because 3.92 with stock tires would be too busy for my use (mostly highway driving). But if I were planning larger tires (which I'm not), I would have spec'd the 3.92.

I really wish FCA would offer the 3.55 with the ED. At least for me, that would be the sweet spot.

 

[MayhemMOORE]

I went from a '20 Bighorn with the 5.7 and 3.92's to a '21 Laramie with the 5.7 and 3.21's. With the 3.92's I felt like the truck was halfway though the gears before I had even gone 100' down the road, whereas the 3.21's hold the lower gears a bit longer which helps smooth out the acceleration and leads to less hunting at slower speeds. As most of my driving is highway, and I don't tow that heavy often enough to worry about it, I was ok going with the 3.21's. I definitely notice better overall mileage now compared to the previous truck. It's not much, maybe 1-2mpg, but it'll add up over time. My only complaint is that it seems to kick out of 8th on even the slightest incline, although the heavier tires aren't helping that.