2023 5.7L V8 HEMI MDS VVT eTorque Engine 3.21 Rear Axle Ratio

[GTyankee]

The way that i always thought about rear differential ratio
At the drag strip that is 10 miles long

Both vehicles identical in every way except the rear differential ratio

The 3.92 ratio will leave the 3.21 ratio in the dust
at about the 8 mile point, the 3.21 Ratio will be side by side with the 3.92 & starting to inch ahead

 

[gwilburn]

Personal observation, from a guy who has maintained a CDL for 40 years and tows an RV a lot: If you're running 70-75 MPH pulling a 28' trailer with a 1500-sized truck, you're going to kill someone. I have a RAM 2500, with a 15,000# tow capacity, pulling a 10,000# 30-foot trailer, and my rule is never...never...tow faster than 65. And that is only on the flat, no one-around freeway, like I-10 or I-40 in the middle of New Mexico and Texas. No one is ever in that much of a hurry.

And 2800 feet elevation is still foothills where I come from.

2800 isn't much... but Ford tests their F-series transmissions here

As for the speed... that's your opinion, and you're entitled to it. I've done this for a long time too. I do slow down when the roads are snow-covered, but I'm certain you would not approve either

 

[gwilburn]

There is no difference.

Your wife asks you to go to the market and get a dozen eggs. There are two vendors, Jack and Jill.

Jack is selling 4 cartons with 3 eggs each.
Jill is silling 3 cartons with 4 eggs each.

Does it matter who you buy from? 4x3 = 12, just like 3x4 = 12.

Same with gear ratios.

Transmission gear * rear axle ratio = final gear ratio

Both trucks give you pretty much identical final gear ratios available for you while towing in the city and on the highway.

The reason the tow rating is different is because from a dead stop the transmission in the 3.21 can't downshift anymore to make an equivalent final gear ratio. So yes from a dead stop the 3.92 will accelerate easier. Once both trucks are moving and in the city/highway? No difference.

Tow ratings are based (among other things) on 0 to 30 and 0 to 60 tests, so obviously in those specific cases the 3.92 will have a high tow rating.

But tow ratings are a silly metric; did you know the v6 with the 3.92 is rated to tow about 800 pounds less than the v8 with the 3.21? Ask yourself if you think that's in any way true to life, if you think the v6 will be even close to the v8. If you think it will, I have this bridge I'm trying to sell ....

The difference is the loads/stress being placed on the drivetrain - specifically the transmission.

Try using a stick as a lever to lift a rock... put the fulcrum close to the rock and the stick is fine. Put the fulcrum a few inches back, and you break the stick.

 

[ramffml]

The difference is the loads/stress being placed on the drivetrain - specifically the transmission.

Try using a stick as a lever to lift a rock... put the fulcrum close to the rock and the stick is fine. Put the fulcrum a few inches back, and you break the stick.

What do you think is more stressful, a transmission towing in 6th gear ("direct drive") or a transmission towing in 7th gear (first overdrive)?

Because my truck tows 90% of the time in 6th, with a 3.92 towing the same load referenced by the OP in this thread I'd be in 7th at the same RPMs, or, I'd have to force a gear limit to 6th and run at 2700 RPMs instead of 2300 needlessly waisting fuel.

Lets separate theory from actual data. Can you find any threads where the transmission has been destroyed or harmed by towing a load with the 3.21, that wouldn't have had any issues when towing the same load with a 3.92? These ZF 8 speeds are bullet proof, many guys build up their trucks and add power or race them, the SRTs use the same transmissions and put out more power and they get tracked etc. It's a non issue.

Also it's my personal belief that any 1500 shouldn't be towing much more than 8000 pounds either, firstly because payload is all to often the limiting factor (not GCWR), and secondly because they build 2500's for a reason to tow these larger loads.

 

[gwilburn]

What do you think is more stressful, a transmission towing in 6th gear ("direct drive") or a transmission towing in 7th gear (first overdrive)?

Because my truck tows 90% of the time in 6th, with a 3.92 towing the same load referenced by the OP in this thread I'd be in 7th at the same RPMs, or, I'd have to force a gear limit to 6th and run at 2700 RPMs instead of 2300 needlessly waisting fuel.

Lets separate theory from actual data. Can you find any threads where the transmission has been destroyed or harmed by towing a load with the 3.21, that wouldn't have had any issues when towing the same load with a 3.92? These ZF 8 speeds are bullet proof, many guys build up their trucks and add power or race them, the SRTs use the same transmissions and put out more power and they get tracked etc. It's a non issue.

Also it's my personal belief that any 1500 shouldn't be towing much more than 8000 pounds either, firstly because payload is all to often the limiting factor (not GCWR), and secondly because they build 2500's for a reason to tow these larger loads.

So why does the manufacturers (ALL of them) build trucks with slower gearing... Please explain how you are correct, and ALL of the manufacturer's engineers are wrong. The OP obviously doesn't like the performance of the 3.21 (and I don't either) - we are both far below the 8000 lbs. you mentioned. Heck, if i towed over 8000 lbs. frequently I'd have a 2500 with a Cummins.

I don't disagree that the transmissions are great... I also don't have the time to spend to prove you wrong.

I can give you another example... The modern snowmobile (what I drag 800+ miles in my trailer) and it's 50+ year old CVT transmission. These put 200+ HP through a CVT via a $200+ Kevlar belt and chaincase (gears). If i take the same machine and gear it up (just a few teeth) I can shred that belt in less than 100 miles (heat from friction). Gear it down slightly, and the same belt will last 4-5000 miles before I replace it from wear. The amount of gearing change would be a factor of 10 less (i.e. 100ths instead of 10ths).

 

[Tulecreeper]

OK, everybody is referring to either the 3.21, or the 3.92. I'm not a gearhead so please forgive if this sounds dumb. Are they only available in the 1500 models? I ask because I don't recall either of those being an option when I ordered my 2500 in January. I think the only options I had were 3.55, 3.73, and 4.10. I went mid-line because, although I tow a lot/often I don't tow heavy a lot, only some/infrequently.

 

[HuskerRam]

OK, everybody is referring to either the 3.21, or the 3.92. I'm not a gearhead so please forgive if this sounds dumb. Are they only available in the 1500 models? I ask because I don't recall either of those being an option when I ordered my 2500 in January. I think the only options I had were 3.55, 3.73, and 4.10. I went mid-line because, although I tow a lot/often I don't tow heavy a lot, only some/infrequently.

Not a dumb question at all. For the 1500 w/ 5.7 Hemi, you can get the 3.21 or 3.92 gears only. The 3.55 is available for the 3.6 (and 3.0 diesel, I think). The 3.73 and 4.10s are for the 2500/3500 only. The default gears for the 2500 are the 3.73, which are good for that application. The 4.10s are an upgrade.

 

[Tulecreeper]

Not a dumb question at all. For the 1500 w/ 5.7 Hemi, you can get the 3.21 or 3.92 gears only. The 3.55 is available for the 3.6 (and 3.0 diesel, I think). The 3.73 and 4.10s are for the 2500/3500 only.

Thanks, I wasn't really sure about the 3.55 when I made that post but I knew when I ordered the truck that 3.73 would be fine for my use. Even if they had the 3.55 offer, I still would have gone with the 3.73 because for me that is perfect. In my last truck - a Silverado, 4.8L, 5-speed manual - I had the 4.XX rear end and although it was great at towing, especially from a dead stop, the mileage really sucked under normal driving conditions. If I got 16 MPG all-around I was doing good.

 

[ramffml]

So why does the manufacturers (ALL of them) build trucks with slower gearing... Please explain how you are correct, and ALL of the manufacturer's engineers are wrong. The OP obviously doesn't like the performance of the 3.21 (and I don't either) - we are both far below the 8000 lbs. you mentioned. Heck, if i towed over 8000 lbs. frequently I'd have a 2500 with a Cummins.

Actually with the increase of 8 and 10 speeds, you're getting less and less choice. Toyota only offers one gear, GM offers one I think unless you get the "tow package" etc.

The 3.21 with the 8 speed, has a deeper first gear than the old 6 speed used in the ram with a 3.92 or 4.10. Think about that.

In fact, the 3.21 with the 8 speed has a deeper first gear than the Tundra's 6 speed with 4.30 gears. It also manages to have a taller final gear than the Tundra, so not only can it pull harder off the line it will have lower rpms on the highway. Win win.

If you read the OP's comment, you'll see that his "problem" is on the highway. The 3.21 will give you pretty much identical final gear ratios as the 3.92 on the highway.

The difference between the gears (WRT towing) is only from a dead stop. But OP isn't complaining about getting moving, he's complaining about power and rpms on the highway, rear axle ratio won't change that in the slightest.

If you study the chart below then you'll see what we're talking about. The chart contains the calculated final gear ratios if both trucs are travelling at 65 mph. The 3.21 cells in orange "match" the 3.92 cells in orange. Same with blue colors etc.

Note how the 3.21 in 6th gear at 65 mph has 2191 rpms, which is identical to the 3.92 in 7th gear at 65 mph at 2194 rpms.

 

[Dusty]

So why does the manufacturers (ALL of them) build trucks with slower gearing... Please explain how you are correct, and ALL of the manufacturer's engineers are wrong. The OP obviously doesn't like the performance of the 3.21 (and I don't either) - we are both far below the 8000 lbs. you mentioned. Heck, if i towed over 8000 lbs. frequently I'd have a 2500 with a Cummins.

The answer is in the advantages of either ratio.

For those carrying within the vehicles payload limits and/or the towing limits, the lower numerical gearset will generally return better fuel consumption, and keep engine RPMs and engine noise lower making it a more pleasant experience when the vehicle is being used just for basic transportation or extremely light duty.

The higher gearset will provide a level of increased performance at launch and across the RPM range, especially when towing heavier loads making the driving experience better for some vehicle drivers.

This is probably why you don't like the 3.21 axle, and there's nothing wrong with that. I've owned two Ram 5.7s with the 3.92s and there is no doubt under any driving scenarios the performance is greater. Except for fuel consumption.

As far as the effects on durability, beyond theorizing there currently isn't enough data or facts to answer that question.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, factory dual exhaust, 18” wheels. Build Date: 3 June 2018. Now at 92855 miles.

 

[gwilburn]

Actually with the increase of 8 and 10 speeds, you're getting less and less choice. Toyota only offers one gear, GM offers one I think unless you get the "tow package" etc.

The 3.21 with the 8 speed, has a deeper first gear than the old 6 speed used in the ram with a 3.92 or 4.10. Think about that.

In fact, the 3.21 with the 8 speed has a deeper first gear than the Tundra's 6 speed with 4.30 gears. It also manages to have a taller final gear than the Tundra, so not only can it pull harder off the line it will have lower rpms on the highway. Win win.

If you read the OP's comment, you'll see that his "problem" is on the highway. The 3.21 will give you pretty much identical final gear ratios as the 3.92 on the highway.

The difference between the gears (WRT towing) is only from a dead stop. But OP isn't complaining about getting moving, he's complaining about power and rpms on the highway, rear axle ratio won't change that in the slightest.

If you study the chart below then you'll see what we're talking about. The chart contains the calculated final gear ratios if both trucs are travelling at 65 mph. The 3.21 cells in orange "match" the 3.92 cells in orange. Same with blue colors etc.

Note how the 3.21 in 6th gear at 65 mph has 2191 rpms, which is identical to the 3.92 in 7th gear at 65 mph at 2194 rpms.

View attachment 523412

I've seen this several times before... those figures being equal, does not mean they are "equal" when it comes to stress on the driveline. There is a reason MFG's offer lower gearing and that equates to higher towing capacities. That's all I'm saying.

The OP also said he doesn't go over 65 mph - in the case of the 3.21, he would almost never be in 8th gear (or would be in-and-out of it constantly). So it absolutely has something to do with highway speeds - especially on 2-lane rolling hills.

I've driven my Dad's 2019 with the 3.21 a lot. It is nicer running 75+ on the interstate. Other than that, I much prefer the 3.92. AND, there's almost no difference in MPG's between our trucks unless we are racing up and down the interstate all the time. He's 84 years old and his MPG is virtually the same as my truck.

As for Toyota Tundra - If you watch some of the towing tests, they had issues with soaring transmission temperatures using that fast rear end (3.31 I think) even with the 10-speed.

 

[ramffml]

I've owned two Ram 5.7s with the 3.92s and there is no doubt under any driving scenarios the performance is greater. Except for fuel consumption.

The "any" is super incorrect. The chart above demonstrates this, and the math for it is:

Torque at the wheels = Engine Torque * tranmission gear ratio * axle ratio.

You can subsitute the axle ratio from 3.21 to 3.92, now you're making more torque right? Not so fast, if you drop a transmission gear in the 3.21 you can make up the difference.

That's why I used the egg carton example.

4 eggs * 3 cartons = 12 eggs: is the same as
3 eggs * 4 cartons = 12 eggs.

(replace "egg" with gears)
1 (trans gear) * 3.21 (rear axle) = 3.21: is the same as
0.82 (trans gear) * 3.92 (rear axle) = 3.2144

You guys are hyper focused on the second variable (rear axle gear), but it doesn't carry any more weight or meaning then the first variable (transmission gear). If you change both variables at the same time, then you can still get a torque multiplication factor of 3.21(44).

 

[ramffml]

I've seen this several times before... those figures being equal, does not mean they are "equal" when it comes to stress on the driveline. There is a reason MFG's offer lower gearing and that equates to higher towing capacities. That's all I'm saying.

Only from a dead stop. That's not what we're discussing. OP's issue is on the highway.

I've towed 7000 pounds with my truck, which is rated for about 8100 or so. It has zero issues taking off from a dead stop even with the 3.21. Where I feel less strong is on a freeway on ramp, or passing semis on the freeway up a hill. Rear gear ratio isn't going to fix that.

The OP also said he doesn't go over 65 mph - in the case of the 3.21, he would almost never be in 8th gear (or would be in-and-out of it constantly). So it absolutely has something to do with highway speeds - especially on 2-lane rolling hills.

The 3.21 will never tow heavy loads in 8th. Not sure what your argument is here. The numerical gear of the transmission is completely irrelevant, what matters is torque multiplication; how much are you multiplying the torque of the engine, at the wheels? And this is a factor of 2 variables: transmission gear ratio * rear axle ratio.

I've driven my Dad's 2019 with the 3.21 a lot. It is nicer running 75+ on the interstate. Other than that, I much prefer the 3.92. AND, there's almost no difference in MPG's between our trucks unless we are racing up and down the interstate all the time. He's 84 years old and his MPG is virtually the same as my truck.

This is irrelvant. I'm not getting into an MPG discussion when this thread is talking about highway towing.

As for Toyota Tundra - If you watch some of the towing tests, they had issues with soaring transmission temperatures using that fast rear end (3.31 I think) even with the 10-speed.

You should see all the rams that have transmission heating issues on this forum. That's across the board, 3.21 and 3.92. But guaranteed it's easier on the transmission for the 3.21 to tow in 6th vs the 3.92 in 7th/overdrive.

 

[Dusty]

The "any" is super incorrect. The chart above demonstrates this, and the math for it is:

Torque at the wheels = Engine Torque * tranmission gear ratio * axle ratio.

You can subsitute the axle ratio from 3.21 to 3.92, now you're making more torque right? Not so fast, if you drop a transmission gear in the 3.21 you can make up the difference.

That's why I used the egg carton example.

4 eggs * 3 cartons = 12 eggs: is the same as
3 eggs * 4 cartons = 12 eggs.

(replace "egg" with gears)
1 (trans gear) * 3.21 (rear axle) = 3.21: is the same as
0.82 (trans gear) * 3.92 (rear axle) = 3.2144

You guys are hyper focused on the second variable (rear axle gear), but it doesn't carry any more weight or meaning then the first variable (transmission gear). If you change both variables at the same time, then you can still get a torque multiplication factor of 3.21(44).

I get your point, but the comparison is valid when the two axle ratios are compared at a steady state speed, each having the transmission in the gear with the similar ratio. And, yes, approximately the same amount of torque will be delivered to the rear wheels.

But in driving where the vehicle is constantly accelerating from a stop or from a mid-range speed, depending on throttle pressure the transmission will likely shift into the next higher gear sooner with the 3.92 ratio, making that comparison difficult.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, factory dual exhaust, 18” wheels. Build Date: 3 June 2018. Now at 92912 miles.

 

[ramffml]

I get your point, but the comparison is valid when the two axle ratios are compared at a steady state speed, each having the transmission in the gear with the similar ratio. And, yes, approximately the same amount of torque will be delivered to the rear wheels.

But in driving where the vehicle is constantly accelerating from a stop or from a mid-range speed, depending on throttle pressure the transmission will likely shift into the next higher gear sooner with the 3.92 ratio, making that comparison difficult.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, factory dual exhaust, 18” wheels. Build Date: 3 June 2018. Now at 92912 miles.

What my chart shows, is that the last 5 gear ratios the trucks use while towing, are nearly identical (close enough the differences don't matter).

What's your definition of "mid range"? Because first and second go by extremely fast in my truck, and once I'm in third there is no difference anymore. And again, my truck doesn't feel weak in first or second. That's actually where I feel the most power (as you'd expect, that's where the torque multiplication is highest). I don't need more power in the city in stop and go traffic at every stoplight. Where I feel the weakest is on an on-ramp (3rd or 4th, trying to go from 30 KM/h to 105 KM/h to safely merge on the freeway), or passing a semi up a hill; gear ratio won't change a thing there.

There are differences, and there are differences that actually matter. I keep coming back to the example of the v6 with the 3.92 being only 800 pounds or so short of the v8/3.21. That's the official tow rating difference. But now get in both trucks and tow 7000 pounds, I bet a years wages anyone towing back to back will say the v8 feels strong and the v6 feels like its ready to window the block.

The tow ratings don't tell you the whole story, yet we obsess over these numbers because we all want a single number that nicely simplifies everything for us in a way that we can understand. They can be useful, but many seem to think that towing experience can be reduced to a single number and nothing can be further from the truth.

 

[gwilburn]

Only from a dead stop. That's not what we're discussing. OP's issue is on the highway.

I've towed 7000 pounds with my truck, which is rated for about 8100 or so. It has zero issues taking off from a dead stop even with the 3.21. Where I feel less strong is on a freeway on ramp, or passing semis on the freeway up a hill. Rear gear ratio isn't going to fix that.


The 3.21 will never tow heavy loads in 8th. Not sure what your argument is here. The numerical gear of the transmission is completely irrelevant, what matters is torque multiplication; how much are you multiplying the torque of the engine, at the wheels? And this is a factor of 2 variables: transmission gear ratio * rear axle ratio.


This is irrelvant. I'm not getting into an MPG discussion when this thread is talking about highway towing.



You should see all the rams that have transmission heating issues on this forum. That's across the board, 3.21 and 3.92. But guaranteed it's easier on the transmission for the 3.21 to tow in 6th vs the 3.92 in 7th/overdrive.

I've seen other threads where you beat this drum until everyone just gives up... Evidently your opinion is the one-and-only truth... Almost 1/4th of my current Ram's 98,000 miles has been spent pulling a trailer.

So I give up... You are right and the Automotive Engineers and the rest of us are wrong.
You feel better now?

Let the OP decide.

 

[ramffml]

I've seen other threads where you beat this drum until everyone just gives up... Evidently your opinion is the one-and-only truth... Almost 1/4th of my current Ram's 98,000 miles has been spent pulling a trailer.

So I give up... You are right and the Automotive Engineers and the rest of us are wrong.
You feel better now?

Let the OP decide.

Don't be childish, I used math to prove my point, how about you do the same? Explain to the OP using math how his highway experience will improve with 3.92 gears.

Break it down into calculated torque at the wheels and how that improves on the highway for the OP by swapping his gears.

 

[gwilburn]

Don't be childish, I used math to prove my point, how about you do the same? Explain to the OP using math how his highway experience will improve with 3.92 gears.

Break it down into calculated torque at the wheels and how that improves on the highway for the OP by swapping his gears.

Childish?? Look in the mirror bud.

I already stated real world facts... there is more towing than just a freeking gear ratio chart!

Have YOU ever PERSONALLY towed a 6500 lb trailer with a Ram 1500 4x4 crew with a 3.92 rear end?? Have YOU ever PERSONALLY towed the same trailer with a 3.21??? I HAVE!!!

So, is the OP interested in mathematics or real world experience?? I know what I'd be interested in (and my degree is in Physics and Mathematics).

I apologize to the OP for the argument that followed offering my opinion and experience.

I'm DONE !!!!

 

[ramffml]

Childish?? Look in the mirror bud.

I already stated real world facts... there is more towing than just a freeking gear ratio chart!

Have YOU ever PERSONALLY towed a 6500 lb trailer with a Ram 1500 4x4 crew with a 3.92 rear end?? Have YOU ever PERSONALLY towed the same trailer with a 3.21??? I HAVE!!!

So, is the OP interested in mathematics or real world experience?? I know what I'd be interested in (and my degree is in Physics and Mathematics).

I apologize to the OP for the argument that followed offering my opinion and experience.

I'm DONE !!!!

So... no math to support your assertions then?

That's OK, just don't argue like your opinion counts for more than actual calcuations showing how the torque at the wheel is pretty much identical in the city, on the on ramps, on the highway, passing truckers etc.

That's the beautiful thing about math, it trumps feelings (and memory) every time.

 

[ramffml]

And by the way I never said you couldn't offer your opinion. That's what forums are for, the more the merrier.

But if you keep replying directly to me how my facts are wrong then you need to show using math how they're wrong.