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MPG effect of 3.92 rear end

rott said:
I haven't found a concrete answer...or really any semi-firm answer even on this. I've read the 3.21 is a little "ho-hum" off the line, but the 3.92 would be significantly better. Does that rear end cause a noticeable drop in MPG, either city or highway?
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Although my '19 only has 7180 miles on it as of this writing, I believe I'm beginning to see a pattern.

I have the fuel consumption records for my two previous 4th gen Rams that had the 3.92 axle. I have been comparing those to the fuel consumption of my '19. Although I think it's still a little premature, I appears that the 4th gen Ram 1500s got slightly better fuel mileage around town than the '19. This became especially acute on my current tank as I've been doing a lot of around town Christmas shopping and I'm seeing less than 17 MPG, compared to both the 2010 and 2014 during the same period of comparison (low of 18.04, 18.67). That low a MPG never occurred on either 4th gen until the real low temperatures of January/February.

Technically, this would make sense as higher throttle pressure is required to launch a vehicle with a numerically lower axle ratio.

Best 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. Now at: 007180 miles.
 
Benefits besides 1mpg in fuel economy?

I've had both. If there was a choice, 3.92 is the better of the choices.


ExcursionDiesel said:
Not if he wants the benefits the 3.21 provide. Each have their advantages. Not everyone wants the same thing.
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I was talking to my son tonight Both of my older sons have 4WD Ram 1500's. One is a Gen III and the other a Gen IV. The one with a Gen IV says he averages about 16 on the interstate and he is running about 2000 RPM's. He also said he gets much better at 55-60 where he gets over 20.

I know I shouldn't complain. I really like the truck. I do hope it will do at least 15-16 MPG on the interstate.

I have now had it going on four weeks. It has been in the shop for not going into gear when put into drive. The dealer couldn't replicate the problem. Yesterday, I started hearing a clunk when turning left and hitting a slight incline like turning from the road into a driveway. I am guessing it is the dreaded body mount issue I have been reading about. I will check tomorrow. I guess the fuel economy thing is my venting point. I am done complaining about MPG's.

Thanks guys.
 
meltedcheez said:
Yikes! I put 8,000 on it in the first four months. I do a lot of driving for work but I also haven't said no to any out-of-town weekend trips. ;-)
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Yeah same here...cant wait to take it on a long trip or to the mountains in the snow
 
alacombe said:
I'm at 2,800 miles at 12.1mpg with the 3.92
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Damn well I guess I'm not the only one... **** I thought I'd be getting closer to 20 no big deal hahahah since it being newer vehicles my chevelle probably gets around 8 mpg
 
mhb1638 said:
Own a 4x4 with 3.92 and drive 52 miles daily 1 way and with 9k on the clock, I squeeze out 17.8 hand calculated. the truck is being traded in this weekend for another 2019 ram, but this time a 4x2 with 3.21 gears for better mileage and my truck is all stock. I can't do 17.8 driving 104 miles every day. No way. If it was a short trip in the city, fine. I drive 25m doing 75 and 45m doing 60-65
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Are you not taking a bath on depreciation of the trade-in vehicle? Even if the new one averages 20mpg, it will take you 10 years (and 380k miles) to recoup even $5750. That's driving 104 miles for 365 days a year. If you are only making the drive 5 days a week for work, the savings drop to $4100. Doesn't seem worth it to me, unless you are getting a smoking deal.
 
GregHBNA said:
With a 3.21 sounds pretty typical. If you had the 3.55 or the 3.92, you would definitely not see this downshifting to 7th (or possibly 6th) in the scenario you posted.
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@Troop2865 does have 3.92's and it is downshifting.
 
I use my truck as a commuter during the week. 60% interstate, 20% highways, 20% stop and go. On the weekends the wife and I sometimes travel to the beach which is all interstate, and during the winter I ride motocross so I travel all highway with a 250# bike in the back plus gear. No
Biggie. Summertime we pull a 20’ pontoon boat to the lake. The lake is - 6 minute drive from the house. I care mostly about mpg. I don’t race around. It sounds like I should look at 3.21’s for my new truck by reading through this thread. Is that the general consensus anyways ?
 
If you don't need the extra 3100 lbs of legal towing weight, then either ratio will be fine.

If you want to try to get more MPG go 3.21, or something other than a truck.

If you want to have a bit more power, go 3.92.

Just remember, dependent on your driving style someone with 3.92 may get better gas mileage than someone with 3.21. Changing your gears isn't going to change this...it is a driver experience and terrian issue everyday.

Good luck with your choices. Modern day trucks don't really make much difference...why there aren't as many rear gear options any more.
 
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I have had 4 Ram's now with every gear ratio. I was going to build a truck and opt for 3.92. I found a truck on the lot that someone had ordered with every option except bed liner and I had the dealer do a linex. My new truck has 3.21 and to be honest I am very happy. The 3.21 actually suits my needs very well as I travel on the highway a lot. I seldom tow and the Hemi has plenty of power, I just came from and eco diesel. At 51 years of age I could care less how fast a 3.92 gets off the line or performs, I'll take the mpg all day and everyday. I believe the 3.21 gives you more then 2mpg over the 3.92. Get what you like it's your money and everyone uses their trucks differently. Mine is a big family vehicle.
 
mxracer32 said:
I use my truck as a commuter during the week. 60% interstate, 20% highways, 20% stop and go. On the weekends the wife and I sometimes travel to the beach which is all interstate, and during the winter I ride motocross so I travel all highway with a 250# bike in the back plus gear. No
Biggie. Summertime we pull a 20’ pontoon boat to the lake. The lake is - 6 minute drive from the house. I care mostly about mpg. I don’t race around. It sounds like I should look at 3.21’s for my new truck by reading through this thread. Is that the general consensus anyways ?
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With your high use of interstate highways and concern for mpg, I'd get the 3.21. The 3.92 takes a nose dive on economy above 65 mph.
 
ExcursionDiesel said:
I sure hope there are real gains to be made! Let us know.
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So i have about 145 miles on the truck just from running around today here's my initial Impressions

  • Transmission shifts more smartly in regular and cruise control situations /I'll explain/
Before if say i was cruising at 55-70 and the transmission was in 8th gear, it would actually try and lug and stay in 8th with a little more throttle, then it would seemingly abruptly drop to 6th once you applied even more throttle, NOW if you're cruising and apply pressure for speed it'll drop to 7th THEN 6th if you keep going

  • MDS kicks in A LOT MORE, I was cruising at 70 on I10 and it actually kicked in
  • E-Torque feels smoother, less jerky when leaving from stops
As for MPG, I can't fairly judge it today due to it being pretty gusty today and I was driving head on into said winds, that being said my average MPG which has around 500Miles on it since its last reset has rose from 15 to 15.6, this is mixed driving in the city purposely watching fuel and driving more agressively on the Freeways

Attached is the updates they gave my truck
 

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Reduxalicious said:
So i have about 145 miles on the truck just from running around today here's my initial Impressions

  • Transmission shifts more smartly in regular and cruise control situations /I'll explain/
Before if say i was cruising at 55-70 and the transmission was in 8th gear, it would actually try and lug and stay in 8th with a little more throttle, then it would drop to 6th once you applied even more throttle, NOW if you're cruising and apply pressure for speed it'll drop to 7th THEN 6th if you keep going

  • MDS kicks in A LOT MORE, I was cruising at 70 on I10 and it actually kicked in
  • E-Torque feels smoother, less jerky when leaving from stops
As for MPG, I can't fairly judge it today due to it being pretty gusty today and I was driving head on into, that being said my average MPG which has around 500Miles on it since its last reset has rose from 15 to 15.6, this is mixed driving in the city purposely watching fuel and driving more agressively on the Freeways

Attached is the updates they gave my truck
Click to expand...

Thanks! Looking forward to getting this done to mine now.
 
2WD Limited w/ 3.21 gears:
I just got back from a highway trip from CA to AZ towing a jet ski trailer with a combined weight of about 800lbs. I got 19.2mpg for the trip across the desert.

My everyday drive consists of a one way freeway commute, with moderate traffic, of 30 miles each way and calculating that route only, I am getting 17.1mpg. When I mix in street driving with that commute I am averaging 16.5mpg.

It will probably all go in the toilet next week when I get my 33s installed. LOL
 
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