3.21. vs 3.92 gear

[SpeedyV]

there may be similarities to cooling the transmissions, but the two platforms do not share the same transmissions. the 2500 engines are mated to a 6 speed tranny

Apologies to the OP that this turned into a transmission thread. I'll summarize: Go with 3.92s unless you're overly concerned about fuel economy.

But to @Goatmann...there have been rumors shared about an 8-speed making it to the next-gen HD lineup, but I see two problems with that: (1) The soon-to-be-revealed 2020 "4.5 gen" HD is just a refresh, so it wouldn't seem profitable to make a change now, and (2) economy and emissions are not as important as durability in an HD powertrain. Have you heard anything about next-gen HD transmissions? What about @devildodge or @Jared B?

 

[Ramit392]

It's a new transmission (8HP75 vs. 8HP70). But it took a lot of digging to understand what that last digit means...

Statements from Ram's own press releases:

• New generation of TorqueFlite eight-speed automatic transmissions provide improved efficiency with more powerful control computers
• The 5.7-liter HEMI V-8 uses an upgraded TorqueFlite 8HP75 transmission.
• Both transmissions use a new generation of computer controllers that process data faster and coordinate transmission operation with the eTorque mild hybrid system. There are more than 40 individual shift maps to optimize shift changes and points for fuel economy, performance and drivability.
• The 2019 Ram 1500 continues to use the thermal management system to bring the transmission fluid and engine oil to operating temperature quickly. The system also serves a cooling function under high load/high ambient temperature conditions to ensure the transmission fluid temperature is controlled.
• 2019 Ram 1500 models employing the legendary 5.7L HEMI V8 utilize the new TorqueFlite 8HP75 transmission, with a torque capacity of 545 lb-ft.

More comments from other sources:

• The eight-speed has been upgraded with weight reductions and durability upgrades (Allpar).
• ...Ram has upgraded their 8-speed automatic for the 2019 Ram 1500. The truck will launch with the 5.7L HEMI V8 and the higher-rated 8-speed that backs it up. Ram updated some hardware and software to make the transmission handle higher loads and operate more smoothly...(TFLtruck).
• Wikipedia shows the 8HP75 (2nd Generation) being used in the 2019+ Ram (DT) and rated for 750 N-m, whereas 2018 and earlier Rams (DS) use the 8HP70, rated at 700 N-m.
• The 8HP75 is stronger than the 8HP70 and will hold 50 more N-m (553 lb-ft capacity on the 75 compared to 516 for the 70). It shifts faster and is supposedly more efficient too (less parasitic loss) (Ramforumz).

And maybe the best source of detailed information is from an obscure site:

• The ZF 8HP75 transmission transfers power from the engine to the road through 4 planetary gearsets and 5 multi-plate clutch pack. To increase both operating and fuel efficiency, the ZF 8HP75 transmission is designed to only keep two of its five clutches (3 rotating and 2 brake) open at any given time. This significantly reduces spin losses, and the little springs between the clutch friction elements, help to keep the clutch completely open to improve both efficiency and the transmission’s coasting function. This ZF 8HP transmission can also immediately downshift from 8th to 2nd gear when maximum performance is required.
• To provide compatibility with hybrid drivetrain components, the ZF 8HP75 transmission control unit has been upgraded to process commands significantly faster. Some applications will have as many as 40 individual shift maps, along with compatibility with thermal management systems. The ZF 8HP75 hydraulic impulse oil storage system (8HP75 HIS System) has been reengineered to provide much faster reaction when coupled with an engine start/stop system. Additionally, the 8HP75 transmission works with shift-by-wire setups, and the ZF 8HP75 transmission fluid is said to last a lifetime of the vehicle. However, it is highly recommended to perform a transmission fluid change at normal intervals (Transmission Repair Cost Guide).

Nice! Its most certainly a different Generation tranny. Thank you for sharing your research Sir.

 

[devildodge]

Apologies to the OP that this turned into a transmission thread. I'll summarize: Go with 3.92s unless you're overly concerned about fuel economy.

But to @Goatmann...there have been rumors shared about an 8-speed making it to the next-gen HD lineup, but I see two problems with that: (1) The soon-to-be-revealed 2020 "4.5 gen" HD is just a refresh, so it wouldn't seem profitable to make a change now, and (2) economy and emissions are not as important as durability in an HD powertrain. Have you heard anything about next-gen HD transmissions? What about @devildodge or @Jared B?

Rumor was 8speed in HD. Not sure if the rumor is pointed atthe 2019 4.5 Gen or the 2021 full redesign.

That said the transmission in the present HD is totally different than the 1500...6 speeds being the most obvious (there are 3 different HD auto trans and the G56 manual...not getting into them for this thread)

The 8speed that is rumored will be nothing like the 8speed in the 1500.

3.92 gears for 1500, 4.10 for HD but 3.21 and 3.73 will be just fine too...the differences are minimal, except the rise in GCWR and highway speeds over 65mph.

The Cummins makes it easy only 3.42 available...lol

 

[Ramit392]

Devildodge and SpeedyV...Thanks for the information even if we did get off track some what. You guys along with all the members here are the parts of what makes this such a great site! Learning new things for all of us!

 

[slimchance]

i see all these threads about how the 392 rear will kill my mpg .. for the past 10 yrs, after giving up on dodges, i have driven toyota tundras with the 433 rear ... yes i said 433 rear .. and overall my mpg local hand calculated was 16 mpg and highway was 18 - 19 mpg ..... this was with the 5.7 engine and a quad cab 6.5' bed and cap .... towing was very easy, 7500# trailer and 10.5 mpg .... so, i think it is the driver as much as the rear that delivers poor mpg and IF you are going to tow anything get at least the 392 and not the 321

 

[PorBoy]

I had the 3.21 before and not that I complained, but I refused to leave the 3.92 off the table on this deal. No I don’t tow / haul / carry, but I do want that powere there if and when I am in need...

 

[NDanecker]

One thing to note though (in reference to the 4.33 rear of the Tundra) is that the final ratio (motor to wheels) is what's important. Comparing the 4.33 of the Tundra to the Ram may not be fare as we don't know what their overdrive (last gear) ratio of the trans is along with tire diameter. Like I said final ratio is what's important not just what the rear end ratio is. Most may already be aware of this but just wanted to throw that out there for the shopper comparing apples to oranges.

 

[runamuck]

One thing to note though (in reference to the 4.33 rear of the Tundra) is that the final ratio (motor to wheels) is what's important. Comparing the 4.33 of the Tundra to the Ram may not be fare as we don't know what their overdrive (last gear) ratio of the trans is along with tire diameter. Like I said final ratio is what's important not just what the rear end ratio is. Most may already be aware of this but just wanted to throw that out there for the shopper comparing apples to oranges.

my nephew had a 2016 tundra 5.7 4x4 with the 4.30 rear end. it pulled great but got 7-8 mph towing and had a small gas tank so he had to stop often. I think the newer ones come with 38 gal. tank so range is better. they pull great but like the rams they have less cargo capacity so he traded for a ram 2500.

 

[slimchance]

my wifes and my tundras both had 38 gal tanks and driving down the road at 60 mph the tach said 1800 rpm ... that is about what both our 2019 rams say ... don't get me wrong i like the rams very much, have the 392 and avg overall (hc) 18-19 mpg

 

[riccnick]

The 5.7L in the Tundra punches way above its weight class, and the rest of the truck is stout (heavy). They get **** for mileage but they pull like an ox and are stable doing it too. Loved the two that I had. The Ram is way nicer and rides better, but it doesn't pull as well (2 valve pushrod vs quad cam 32 valve VVT-i) and doesn't feel as stable either. However, as with any modern truck, even half ton's, we're talking a relatively small difference between them all as far as capability goes. The Ram pulls just fine, even with my 3.21's and 8,000lbs on the hitch. The 3.92's will pull better, and so far, from what I've seen out of my 3.21's and read about with the 3.92's, the gas mileage difference is essentially zero.

 

[Electrical]

This is getting convoluted to the point of being careless. Drawing Ram conclusions based on Toyota may not apply. 3.92 may get same economy city but certainly has a large effect highway.

 

[Ramit392]

Large effect? 1 to 2 mpg I suppose could be large to some but for the benefits of a 3.92 its by far worth it imo only.

 

[19llhpb]

Large effect? 1 to 2 mpg I suppose could be large to some but for the benefits of a 3.92 its by far worth it imo only.

Absolutely. I appreciate the wide variance that Ram offers. Ford I believe offers a 3:31, 3:55, and a 3:73. Ram offering a 3:21, 3:55( with V-6) and the 3:92 gives a somewhat ‘wider’ scope. Myself, who isn’t as concerned with mpg’s, opts for the 3:92 for towing and working. Glad Ram also offers the 3:21 for those who use their truck as a family vehicle or a long distance work commuter on the highway everyday and want better mpg’s. Glad those folks are able to enjoy/drive a nice full size pickup and get better mpg’s. IMO Ram offers the best of both world’s with these gear ratios.

 

[Ramit392]

Absolutely. I appreciate the wide variance that Ram offers. Ford I believe offers a 3:31, 3:55, and a 3:73. Ram offering a 3:21, 3:55( with V-6) and the 3:92 gives a somewhat ‘wider’ scope. Myself, who isn’t as concerned with mpg’s, opts for the 3:92 for towing and working. Glad Ram also offers the 3:21 for those who use their truck as a family vehicle or a long distance work commuter on the highway everyday and want better mpg’s. Glad those folks are able to enjoy/drive a nice full size pickup and get better mpg’s. IMO Ram offers the best of both world’s with these gear ratios.

Yes sir. 100% agree. I suppose over many years at 1 to 2 mpg the cost would be significant in the long run I failed to mention as well. The 392 in our life goes on vacations, pulls Tandem wheel flat bed with gators and such loaded,pulling Pontoon on fishing trips and in bad weather wife drives the truck to work 45 miles one way. Combo driving always between 18 to 19 MPG. Cannot complain about the mpg. and the 392 is all around best gear for our life around here. The 3.21 is a great gear had it in one of several Rams back. Had the 355 one time with 5.7 as well some Rams back. Really could not tell difference much between the 321 and the 355.

 

[CnyRver]

I have about 700 miles on my ‘19 with 3.21 rear and a soft bed cover. Averaging 12mpg(actual calculation not using computer). That’s with lots of remote start idling and winter gas. Think my ‘16 Ram did about 14 mpg under same conditions with 3.92 rear. I definitely did much better in the summer months, prolly about 17 mpg overall with a heavier foot on the ‘16. If I had a chance to pick a 3.92 rear equipped ram again I would. I thought since I wasn’t towing anymore the 3.21 would be easier at the pump but so far not happy. Honestly they should all be equipped standard with a 3.55 and optional towing 3.92. The base 3.21 doesn’t cut it in my opinion only allowing 8,150 lbs towing. Would like to see about 10k tow rating standard.

 

[Ramit392]

I have about 700 miles on my ‘19 with 3.21 rear and a soft bed cover. Averaging 12mpg(actual calculation not using computer). That’s with lots of remote start idling and winter gas. Think my ‘16 Ram did about 14 mpg under same conditions with 3.92 rear. I definitely did much better in the summer months, prolly about 17 mpg overall with a heavier foot on the ‘16. If I had a chance to pick a 3.92 rear equipped ram again I would. I thought since I wasn’t towing anymore the 3.21 would be easier at the pump but so far not happy. Honestly they should all be equipped standard with a 3.55 and optional towing 3.92. The base 3.21 doesn’t cut it in my opinion only allowing 8,150 lbs towing. Would like to see about 10k tow rating standard.

Yes that makes for perfect thinking. Many say the 8 speed can do as well with the 321 as the 355 when they were 6 speeds. Supposedly that is why the 355 was ruled out in the 5.7 next year after the introduction of the 8 speeds.IMO most buying a truck nor really concerned all that much with MPG. vs. the pulling and payload Caps.

 

[Electrical]

Large effect? 1 to 2 mpg I suppose could be large to some but for the benefits of a 3.92 its by far worth it imo only.

Large. Eh. Maybe "noticeable" woulda been a better way to say it.

Some others have noticed earlier that the drivetrain ratios for someone with a 3.21 in 7th gear turns out to be very close in engine RPM's to a 3.92 in 8th gear. Granted, losses between 7th and 8th may not be identical, and the engine RPM match is not perfect, but it still seems this is a relatively good way to directly compare the difference in economy.

So... I tested this... in my Hemi Durango. I wish someone with 3.21's in a Hemi Ram would also.

My Durango has the prior gen 8-speed (8HP70) but the gearing is still the same. Rear axle is 3.09. Hemi engine, obviously non-etorque. I chose a stretch of flat highway about 15 miles long with no traffic. I ran it two times back to back, both at 65 mph with the cruise set, once in 8th gear and the other in 7th. 7.5 miles out and 7.5 miles back; identical loops both times. My result?

8th gear = 26 mpg indicated
7th gear = 23 mpg indicated

My indicated is typically a couple mpg's higher than hand calculated, but regardless, a noticeable delta exists... 13%. Some might call that large.

In my humble opinion there's a lot of mis-comparisons and unqualified statements thrown around... leading people to extend discussions and draw conclusions based on things that may not warrant doing so. And we all know what happens when we hear something often enough; fiction becomes truth.

 

[NDanecker]

I think some of the numbers people are posting are a result of different measurements. Some use the lie-o-meter. Some hand calculate. Some take a 20 mile road trip, baby the truck, get a high number and then brag with a post "I get 22 mpg average!'. Others take a true multiple tank hand calculated average. Of course we will see a wide swing. Lots of variables here from one person to the next like terrain, elevation, gas, driving style, gears, tires, weight, e-torque, no e-torque, disable MDS, leave MDS on - list goes on and on.

IMO, a snapshot mpg number taken on a few mile road trip using the lie-o-meter means nothing. Anyone can get a nice mpg number if the conditions are right. It is useless. To make my point on another forum board I did a test managing to 28mpg in my DRW diesel with AISIN and 4.10 gears (truck weighed over 9k lbs) but my true multiple tank average was 14.6 hand calculated over 14,600 miles. Guess my point is don't take numbers as fact until you find out how they came to that number, and also consider what you are using the number for. If for budget reasons then obviously use a multi-tank average. If for bragging rights then use the 22mpg snapshot number that is all highway.

In the end remember that it is a truck and not a Prius. If you are finding yourself complaining about a few mpg variance from the next guy then you are probably in the wrong vehicle. Just my opinion....

 

[lambone]

I love my Laramie but I really hope I don’t regret choosing a truck with the 3.21 gearing. I’ve put heavier tires on and already notice a difference in gas mpg and acceleration.

Time will tell as camping season is just around the corner. If the truck is a dog pulling my camper I see myself wanting to “upgrade” to the 3.92 Rebel.

Specs on my trailer are:
Dry weight- 4 505lbs
GVWR - 7,000lbs
Tongue weight - 6-700lbs

Not to sidetrack but I just wish the Rebel had heated and reclining rear seats like the Laramie. This is a big feature for the kids on road trips...

 

[Ramit392]

I love my Laramie but I really hope I don’t regret choosing a truck with the 3.21 gearing. I’ve put heavier tires on and already notice a difference in gas mpg and acceleration.

Time will tell as camping season is just around the corner. If the truck is a dog pulling my camper I see myself wanting to “upgrade” to the 3.92 Rebel.

Specs on my trailer are:
Dry weight- 4 505lbs
GVWR - 7,000lbs
Tongue weight - 6-700lbs

Not to sidetrack but I just wish the Rebel had heated and reclining rear seats like the Laramie. This is a big feature for the kids on road trips...

IMO you will be just fine with 4505 weight towing with the 3.21. to camp grounds. I think longer hauls and weight upwards of 8000 lbs the 3.92 would make a difference in "PushbacK" but no so much with 4500 Lbs.