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2019 RAM 1500 Tradesman 4X2 EcoDiesel
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Actually, real-world testing (and personal experience) shows the opposite. There's very little difference between 3.21 and 3.92 when doing the 0 - 60 test or 1/4 mile testing. The real difference is when you take a trailer (at max load) over a mountain pass. The 3.21 can't maintain speed, not even in a lower gear. I've literally had my 2015 (with 3.55 gears) slow down to 28 mph on a long steep grade. Why? Because the truck can't maintain speed, so I end up in a non-towing gear and the truck feels gutless. This is why the 3.92 EcoDiesel is rated to tow more than the 3.21 EcoDiesel.

SlowRoller, it doesn't sound like you're towing near maximum capacity and/or towing on long steep grades, so you might not have major cooling issues. If you run into cooling issues, there are three things that you can do to help.
1. Change to the honeycomb style grille if you have one of the restrictive grilles.
2. GDE offers a lower temperature thermostat that reduces coolant and oil temps about 18*F.
3. Tune

The 2020+ 3rd gen EcoDiesel DOES NOT have a cooling issue, which is why it's towing capacity is more closely rated to the Hemi etorque.
Your post above made a great case for the difference based on low gear launch capabilities. I just can't see why the 3.21s would have more trouble cooling or pulling at the same RPMs and overall gear ratio. I think in the 40-50 MPH range, you'd be in 3rd or 4th gear with 3.21s, where they have a noticeably lower overall ratio, therefore higher RPMs (3 and 6% respectively) and "pull". I don't know if 6% higher RPMs would cause cooling problems, but the engine would pull better.

I haven't had major cooling issues. My oil hit 253 F once. I have the Tradesman grill and only pull around 5,000#. I have driven long, steep grades in CO and CA, but CO was in April, so not terribly hot, especially at 10,000'. Like you, I have 3.55s, so some (dis)advantages compared to the other two ratios.

On Memorial Day, we went over Donner Summit instead of our planned route to Lassen through Red Bluff and Anderson, where 109F was predicted (maybe only 104 when we would have gone through).
 

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basically the taller the gear ratio/final drive the more power you need to pull the same weight. it only becomes a problem when you introduce a resistance and as the resistance goes up the taller gear has to shift down. eventually the taller gear will run out of shifting down before the shorter gear. eventually the taller gear won't be able to move it and the shorter gear will be able to.

it's actually very simple
the 3.92 can pull more from a dead stop than the 3.21, so as you approach a resistance nearing a dead stop the short 3.92 gear wins. every single time all else equal.

so the 3.21 runs out of gear before the 3.92 with the same weight.
 

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2015 Outdoorsman EcoD CC w/6.4' 4X4
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Getting the load rolling isn't the problem.

You can point calculations all you want, just because an engine is spinning at XXXX rpms doesn't mean it's actually the same in two different scenarios.
Start at the load and work your way forward. Towing 7K lbs comsumes XXX amount of power to maintain the speed your moving. At the input of the differential the 3.21 requires XXX amount of power where as the 3.92 is 20% less. That is the load that present to each gear of the engine/transmission.

3.21 at 65mph in 7th 1820 rpm
3.92 at 65mph in 8th 1720 rpm

3.21 at 65mph in 6th 2200 rpm
3.92 at 65mph in 7th 2250 rpm

3.21 at 65mph in 5th 2900 rpm
3.92 at 65mph in 6th 2650 rpm

3.21 at 65mph in 4th 3800 rpm
3.92 at 65mph in 5th 3550 rpm

3.21 at 60mph in 4th 3360 rpm
3.92 at 60mph in 5th 3250 rpm

You can see how fast the rpms get out of hand maintaining the same speed.
The 5/6 split is where the 3.21 might be able to hold the load, 4th gear turn into a high rpm option.
There will be more cases where the 3.21 trans will have to downshift where as 3.92 won't need to.
 

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2019 RAM 1500 Tradesman 4X2 EcoDiesel
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Getting the load rolling isn't the problem.

You can point calculations all you want, just because an engine is spinning at XXXX rpms doesn't mean it's actually the same in two different scenarios.
Start at the load and work your way forward. Towing 7K lbs comsumes XXX amount of power to maintain the speed your moving. At the input of the differential the 3.21 requires XXX amount of power where as the 3.92 is 20% less. That is the load that present to each gear of the engine/transmission.

3.21 at 65mph in 7th 1820 rpm
3.92 at 65mph in 8th 1720 rpm

3.21 at 65mph in 6th 2200 rpm
3.92 at 65mph in 7th 2250 rpm

3.21 at 65mph in 5th 2900 rpm
3.92 at 65mph in 6th 2650 rpm

3.21 at 65mph in 4th 3800 rpm
3.92 at 65mph in 5th 3550 rpm

3.21 at 60mph in 4th 3360 rpm
3.92 at 60mph in 5th 3250 rpm

You can see how fast the rpms get out of hand maintaining the same speed.
The 5/6 split is where the 3.21 might be able to hold the load, 4th gear turn into a high rpm option.
There will be more cases where the 3.21 trans will have to downshift where as 3.92 won't need to.
Your figures show that 3.21s in 5th gear would produce about 29% more power to the rear end (using your terminology) than 3.92s in 6th gear and 9% more to the wheels. That is the example among yours where you're towing pretty hard**. On a steep enough grade, the 3.92s might have to shift to 5th, going to 3550 RPMs, which might prompt you to slow down to 55 MPH to keep it around 3,000.

**The last two scenarios don't seem appealing for EDs, where most folks seem to keep it below 3,000 RPMs, although the gassers would be running there, from what I've heard.

One peculiarity that I noticed is that this and a similarly titled thread don't appear in the list of new posts/What's New! I will be curious to see if this comment changes that.
 

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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
I have 2 ecodiesels and one has the 3.92 and one has the 3.21. I like the pep off the line with the 3.92s in my 2014 but the 3.21s really are fine. Unless you need to max tow there is zero reason to get the 3.92s, I keep 30+ on the Highway day in and day out. I just went thru the smoky mountains from Chattanooga to Winston Salem NC and averaged 30 the whole trip.
 

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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
I have a crew cab 4x4 ED with 3.21s.... When they first built the 2020s as far as I know that was the only gear offered.
 

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2021 Ram 1500 EcoD Laramie 4x4 crew cab ORP w/all the goodies
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So if you bought the truck solely for MPG: 3.21

If you bought the truck to use as a truck: 3.92
Appreciate your posts here and the couple of informative youtube clips as well. Seems like you tow a fair amount which is great. But “3.21 solely for mpg and 3.92 to use as a truck” is binary. Many of us that purchased an EcoD want both – decent mpg and good use of a truck.

Despite the 3.92 gearing on my ’21 EcoD, cumulative-to-date I’m seeing roughly 38% better mpg over the ’17 hemi that had 3.21 gears. Definitely pleased but thought I would see about 50% improvement (all hand calced or fuelly). On a serious note, that is a HUGE bump. No complaints, just an observation. But I do believe the gearing of the 3.92s has limited the improved mpg based on my driving habits (some fast freeway speeds & moderate loads but not heavy footed acceleration and no heavy towing). And I also believe that the all-terrain Falken tires on the ’21 EcoD are reducing the mpg slightly versus the all season tires on the ’17 Hemi that had 3.21.

As for use as a truck? I use it to haul #hit all the time. Like many others, the stuff being transported doesn’t usually weigh that much but it takes up a lot of space and wouldn’t work in an SUV. Like a freshly harvested bloody 180lb wild boar, tons of ice, and gear in the prior Laramie.
IMG_9814-b.png


Or a Bluefin Tuna soon to be loaded in the bed.
IMG_0123-b.jpg


Weigh station while on a typical road trip hauling “people, gear and stuff” with the weight (just the Ram, no trailer) about 350lbs below the GVRW listed by Ram.

P1000879-Weight.JPG
 
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Your figures show that 3.21s in 5th gear would produce about 29% more power to the rear end (using your terminology) than 3.92s in 6th gear and 9% more to the wheels. That is the example among yours where you're towing pretty hard**. On a steep enough grade, the 3.92s might have to shift to 5th, going to 3550 RPMs, which might prompt you to slow down to 55 MPH to keep it around 3,000.
There you go assuming that a particular rpm equates to a certain power output, I'll say it again just because an engine is spinning at XXXX rpms doesn't mean it's making XXX amount of power. An engine especially one with forced induction is reactive to the load, when more load is applied at a higher value than the engine is capable of efficiency is lost.
Start from the load and work you way backwards, a transmission doesn't make power it uses it also. Every time you drop a gear your adding more gearing loss to to the engine.
 

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There you go assuming that a particular rpm equates to a certain power output, I'll say it again just because an engine is spinning at XXXX rpms doesn't mean it's making XXX amount of power. An engine especially one with forced induction is reactive to the load, when more load is applied at a higher value than the engine is capable of efficiency is lost.
Start from the load and work you way backwards, a transmission doesn't make power it uses it also. Every time you drop a gear your adding more gearing loss to to the engine.
You seem to be saying that the same type of engine is incapable of putting out as much power because a different combination of gears is used to obtain the same overall gear ratio, assuming everything else is the same. What would explain that? Going from 3.21 to 3.92 in the rear end is like dropping a gear, so isn't that "adding more gearing loss to to the engine"?
 

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2014 RAM Big Horn 4x4 Quad diesel
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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.


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A question I doubt anyone here can answer. Why did they drop the 3.55 rear end. Seems like a good compromise to me.
Manufacturers must certify each drivetrain combination for EPA compliance, a very expensive process. The more engine/transmission/differential choices the higher development costs, so manufacturers limit offerings. Giving customers the choice of two differentials is less expensive than three. Thank the EPA for that.

The 3.21 and 3.92 choices bracket what most drivers want. I suspect dropping the 3.55 was purely a business cost decision.
 

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Manufacturers must certify each drivetrain combination for EPA compliance, a very expensive process. The more engine/transmission/differential choices the higher development costs, so manufacturers limit offerings. Giving customers the choice of two differentials is less expensive than three. Thank the EPA for that.

The 3.21 and 3.92 choices bracket what most drivers want. I suspect dropping the 3.55 was purely a business cost decision.
3.55 seems to be preferred by Pentastar owners.
 

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fwiw I lost 2mpg with general at/x E rated 285/60/20 tires. drove in the rain yesterday and instead of skating around on garbage good years I was feeling confidence in the generals. they were pushing water our from under truck like a boat.
 

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I have yet to see anyone explain how "the 3.92 gears will always outperform 3.21 gears when towing at highway speeds" when they give virtually identical ratio choices, albeit in one gear higher.
There is roughly a 20% mechanical advantage between gears. Shifting up or down will change the mechanical advantage of the torque input. Or I could say a mechanical disadvantage when at gears in the overdrive.

One can use a spreadsheet that shows torque at the wheel, (not the same as flywheel torque) per rpm per gear.
 

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2019 RAM 1500 Tradesman 4X2 EcoDiesel
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There is roughly a 20% mechanical advantage between gears. Shifting up or down will change the mechanical advantage of the torque input. Or I could say a mechanical disadvantage when at gears in the overdrive.
I assume you are referring to the ratio changes between sequential gears? They range from 16-33%, mostly around 20%. That was all taken into account in previous comments. The point of contention is whether the truck has less power at the same RPMs by using a different combination of gears to arrive at essentially the same overall gear ratio.
 

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Manufacturers must certify each drivetrain combination for EPA compliance, a very expensive process. The more engine/transmission/differential choices the higher development costs, so manufacturers limit offerings. Giving customers the choice of two differentials is less expensive than three. Thank the EPA for that.
I can't see where different figures are given for different rear-ends. Offering more colors also is more expensive--Henry Ford used to offer one.
Gas Mileage of 2021 Vehicles by Ram (fueleconomy.gov)
 

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2014 RAM Big Horn 4x4 Quad diesel
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This business calculus is very much similar to manual transmissions disappearing from most vehicle line updates.
Stick shifts sell in too few numbers to justify the cost of going through an additional power train certification.
Unless a manual is an integral part of the model identity (sports car, performance) dropping the offering is simply a profit decision for large manufacturers.
 

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Just wanted to chip in with a quick reply. Sold my 99 7.3 powerstroke, awesome engine, but I just did not need that beast. I went with the Ram Bighorn 3:21 and mileage is outstanding about 28 mpg in my rural area. I've tipped 33 on level high way over long stretches. I'm only tacking a little under 1500 rpms at 65 mpg. First tow (about 7 hours each way) with my 18 foot trailer (only 3000 lbs) mileage was 18 mpg. Up big grades, in tow mode, maintaining 65 mph no problem. I only tow about 5 times a year camping so did not beef up on the towing side. Really happy with the truck, love the torque. I never even considered the 5.7, gotta be a gas hog, wanted the new technology. I do have a question, being as you have tow haul mode, why wouldn't you get the 3:21. After my 3/4 ton I admit I would not tow more than 6000 lbs with a 1/2 ton (only rated at 8400 lbs towing I think), I'm just conservative that way. Happy with the baby diesel so far!
 

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Just wanted to chip in with a quick reply. Sold my 99 7.3 powerstroke, awesome engine, but I just did not need that beast. I went with the Ram Bighorn 3:21 and mileage is outstanding about 28 mpg in my rural area. I've tipped 33 on level high way over long stretches. I'm only tacking a little under 1500 rpms at 65 mpg. First tow (about 7 hours each way) with my 18 foot trailer (only 3000 lbs) mileage was 18 mpg. Up big grades, in tow mode, maintaining 65 mph no problem. I only tow about 5 times a year camping so did not beef up on the towing side. Really happy with the truck, love the torque. I never even considered the 5.7, gotta be a gas hog, wanted the new technology. I do have a question, being as you have tow haul mode, why wouldn't you get the 3:21. After my 3/4 ton I admit I would not tow more than 6000 lbs with a 1/2 ton (only rated at 8400 lbs towing I think), I'm just conservative that way. Happy with the baby diesel so far!
Tow/haul is really just converter lockup and shift points which are needed to keep you moving and the trans from overheating. Not going to increase towing weight rating, but I agree I have the 3.21s abs mine tows just fine. I pulled a flat trailer with 3 yards of wet dirt on it and it had zero problems with it.
 
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