3.21 vs 3.92 Gear Ratio...will not be towing much.

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runamuck

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I think that is what I said..with 200# less capacity, he never had any trouble carrying more gear than me..also an earlier poster said the limiting factor is the axle ratings which in my case are actually 800# more than the posted gvwr
 

Gom

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I have the 3.21 with the Hemi, towing package, crew cab 4X4 and I find it more than enough to tow my 18' fiberglass fish and ski boat with a 150hp outboard on it. wife, me, 2 teenagers and 2 yellow labs.
I don't live a mountainous region.
I wanted the 3.92 when I bought it but couldn't find it in what I was looking to spend. Now, I am totally ok with the 3.21.
 

RAM08110719

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Thanks ...with all the Covid stuff I thought I may just config and go but looks like I gotta go old school and test drive the 3.21 and 3.92 for the performance as well as the ride quality of the 20 inch vs the 22 inch tires. My gut says that the 20 inch tires and 3.21 will work the best for what I am looking for ....thanks everyone...really appreciate the advice.


Even when I worked at a dealer. I still test drove before I bought. Must know what it feels like. For some people. They spend the same amount of time in their truck as their sleeping bed. Some even more. So you want it to feel right. When I sold to people. I had a test route. Plus I let them take it any other place they felt would help. With a truck. If parking in your garage is important. Ask to take it to your house. I did that many times. When I sold. I had 1 customer refuse to test drive. I thought. That will be my first return. It was. He found out after driving it he didn't like it. So even with covid. Take a test drive. This is something that plays an important role in your life. If it makes you feel more comfortable. Bring a bottle of alcohol and spray the surfaces down. Everything will be ok. Plus that is part of the fun. If you take 10 identical new trucks. Test drive all 10. You will find they all drive a bit different. They are all unique in their own way. That's because people make them. It will be that way till people are pulled out of the production. That will be a sad day.
 

d_coyne

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I've got the 5.7 with the 3.21 in a CC short bed. I tow a 6500lb boat/trailer combo regularly, over mostly flats and some hills for 3 hour trips. I would say the truck does just fine, but if I were to pull anything more or do more than just hills, I would definitely want the 3.92's. If you aren't towing over 6000lb or through the steep hills/mountains, go with the 3.21's. If anything else, do the 3.92's.
 
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moulin6801

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I have the 3.21
Tow boats with no problems...
Look at those guys in Europe, towing all kind of crap with the smallest of cars...
Only if you your job, farm etc would you have towing lots of weight all the time, I would get a bigger rate..
PS 155K miles, no problems
 

pacofortacos

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I think that is what I said..with 200# less capacity, he never had any trouble carrying more gear than me..also an earlier poster said the limiting factor is the axle ratings which in my case are actually 800# more than the posted gvwr

Yeah and that seems about right. You would always want the GVWR to be less than the weakest link - be it axles, brakes, tires, etc.

It seems as if all or almost all half ton pick up trucks have a GVWR or 6800-7100 lbs. - maybe some fed or state regulation reasons?
 

Donn

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RIP @CML1

:signs8:

That'll teach you to ask a simple question around here.
 

Dreedo

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I have the 3.92 gears and tow a 25' travel trailer. Get around 13.5mpg while towing. Without the trailer I get 15mpg around town and 20-21mpg on the highway. The 3.92 gearing does make the truck feel very sporty, quick off the line. Heck you can spin the tires if you want to. I drove both 3.92 and 3.21 when buying and my impression was that stomping the gas with the 3.21 gearing wasn't as much fun. Clearly you'd get better mileage with the 3.21's and for what you are towing it should work fine. Then again.... you don't buy a truck to get good mileage :)
 

OutpostRam

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With the current administration in the white house, gas is going to skyrocket. Here in the southwest, it has gone up .80 cents/gallon in two months.
You may want to consider the V6 since you are trying to eek out every last mpg. Back when I ordered my Laramie CC 4x4 6.4' bed 8 speed 2014, I test drove trucks with the 3.21 and 3.29 gears. My needs fell with the 5.7 and 3.92. Mountainous driving while towing a toy hauler loaded for hunting it was my option. It still does great at 7500 ft elevation and 90,000 miles on the clock. Investigate the V6 for your needs. Gas is going up a dime a week.
 

Johnny_N_TX

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Here's a bit of a sidebar for you that might engage your thought processes a bit...

My truck is a very different setup than yours, but I have had amazing luck with 4.56 gears. I'm in a 2002 with the 4.7(non-HO... the 245hp/315 ft-lbs version), 5 speed automatic, 2wd which is rolling on 33" E-rated tires (much heavier than the crap tires it came with):

Running "empty" at 80 mph (we have highways in Texas that are 85mph rated), on a south Texas highway I am turning 2500 rpms and seeing 18mpg on the trip computer. That number fluctuates a bit depending on incline (going uphill it'll drop 1-2 mpg at a steady state of speed).

If I drop to 70mph on the same highway the rpms drop to 2100, and the MPG goes up to 22; but is much more sensitive to going uphill. It varies more like 2-4 mpg (dropping to 18mpg when I go over an overpass and down to 18-20 on a 1-2% uphill gradient like driving from the coast back to Houston). When cruising at 80mph, it doesn't have this issue.

I installed a data logger (my laptop) and watched the numbers on a trip and it appears is that the volumetric efficiency of the engine is much better between 2300-2700 RPMs for this particular combination. In simpler terms: I am making more power with the same amount of throttle because the engine is operating more efficiently. Oddly, when I run 65mph the fuel economy does not go up. It actually goes down a bit because the engine is not running as efficiently and the truck is moving slower (same amount of fuel burn at a lower land speed). However, at 55mph, my fuel economy goes up again (25-26) which I have NEVER seen in this truck prior to installing the new differential gears and 2nd overdrive (the 5 spd transmission is the same as the 4 spd, but there is a 2nd overdrive ratio programmed to engage ... I love electronic transmissions).

A better method of analyzing your fuel economy would be by volumetric efficiency rather than MPG. You can get 30 mpg in a fullsize truck if you drive 35 miles per hour, but(!!!) it'll take you twice as long to get to work. I would address your problem by setting your goals (limits) in MPH (how far and how long). You have a certain distance to go and a certain time to get there. Now you optimize efficiency by graphing out your expectations against volumetric efficiency (power made vs engine load - or fuel consumption to power output). Then take this data and find the ideal operating range based on your time/distance parameters and select equipment that will best fit those needs. You will need a 3-D fuel map for your truck (should be able to get one fairly easily). This will let you see what the consumption rate is for a given amount of power output vs engine RPM and throttle position. It's a 4 variable equation (actually it's much more than that, but it is able to be reduced to 4 variables... all of which logged data should be available from any company that creates custom fuel maps - like diablo, superchips, etc.). Alternatively, you can experiment like I did, but that could get expensive if you're not happy with your setup. $400/gearset + $400 installation... plus time in the shop... it would be wiser to find the data and make an analysis... unless money is no object.

In my case it was a happy accident. I just wanted to be able to tow my RV at highway speeds without needing to go out of OD when I cross the big ass bridges and overpasses in this area. Discovering the sweet spot for my engine was just icing on the cake; and the "kick in the pants" factor when I'm unloaded is a real hoot and a half. Especially with a truetrac grabbing the pavement. No more spinning tires BS. It just launches.

Good Luck!
 

Jim2015RAM

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I am glad the original poster decided to go with the 3.21 gears; the 8-speed transmission makes that the right choice.
The old 5 and 6 speed transmissions needed the 3.92/4.10 gears.
The 8-speed with 3.21 rear has a lower 1st gear total ratio than those other transmissions with 3.92/4.10 gears.

Thanks to ramffml and pacofortacos for posting lots of good information.

Comparing the 6-speed and 8-speed transmissions, I was surprised to see the ultra low 1st gear in the 8-speed (4.71 vs 3.00 in the 6-speeds for 1500 RAMs).
65RFE 3.00(1st), 1.67(2nd), 1.50(3rd), 1.00(4th), 0.75(5th), 0.67(6th)
8HP70 4.71(1st), 3.14(2nd), 2.10(3rd), 1.67(4th), 1.29(5th), 1.00(6th), 0.84(7th), 0.67(8th)
6-speed (3.92) and 8-speed (3.21) total reduction in various gears:
8-speed: 3.21 x 4.71 = 15.12 (1st), 10.08 (2nd), 4.14 (5th), 3.21 (6th), 2.70 (7th), 2.15 (8th)
6-speed: 3.92 x 3.00 = 11.76 (1st), 6.55 (2nd), 3.92 (4th), 2.94 (5th), 2.63 (6th)

For towing, this results in using an 8-speed with 3.21 gears and just use a lower transmission gear on the highway. For example if 5th works fine with the 6-speed and 3.92 gears, use 6th with the 8-speed and 3.21 gears. First gear total reduction is actually more with the 8-speed and only 3.21 rear gears.

After owning my 2015 RAM 1500 with 5.7 Hemi and 8-speed with 3.21 rear gears; towing my race car in an enclosed trailer for over 5 years. The 3.21 was a great choice.
 

KC5TGQ

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3:21 WILL SAVE you a lot of gas. And 3:21 will pull a load better at speed. A no-brainer.
 

Knock Out

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my 4th gen typically got 19 on the highway. I could get more, sometimes got less. This 5th gen just does not get the mileage my 14 Limited got with the 5.7 and 3.92.
Hello All
New to this forum
I have had many trucks in the past more than 20
Have towed with all of them
Sports cars =many
Muscle cars=many
Jeeps and 4x4 trucks=many
Gears,,Gears ,Gears =the 2nd most important part of any set up (brakes are first)
Currently have 2017 ram 3500 srw 2wd crew cab short box with 6.4 hemi
running 456 gears with 285 65 20 tires
My 30 ft fifth wheel is 14,500 loaded
This truck pulls it easily ,mileage is 10-11 on flat ground, we usually average between 8-9 miles mpg on our trips
My other current truck is 2018 Ram 1500 single cab short box 5.7 hemi 2wd tradesman white truck black grill =very pedestrian
I ordered it with tow package and 392 limited slip rear end
makes for a very fun sleeper with the 8 sp tranny still gets 22 hwy and 18 around town
Hope this helps
KO
 

corneileous

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3:21 WILL SAVE you a lot of gas. And 3:21 will pull a load better at speed. A no-brainer.

Sure, there’s some who will actually agree with you on that but most will tell you that isn’t true. Maybe a lightly loaded or light trailer but most certainly not a heavy one. As I’ve said many times before, there’s a reason the 3.92’s are an option.


Sent from my iPhone using Tapatalk
 

Jim113

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Thanks ...with all the Covid stuff I thought I may just config and go but looks like I gotta go old school and test drive the 3.21 and 3.92 for the performance as well as the ride quality of the 20 inch vs the 22 inch tires. My gut says that the 20 inch tires and 3.21 will work the best for what I am looking for ....thanks everyone...really appreciate the advice.

I purchased a new 2020 Longhorn last year and it has both the 3:21 rear end and the 22 inch tires ... I traded in my 2017 Longhorn which had the 3:92 and 20 inch wheels ... I really don't find much difference in the performance between the two, and the ride of the 2020 is just fine ... If you're just towing a small boat, you'll be OK with the 3:21 and 22 inch wheels ...
 

No Tyme

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Do not get the 22 inch wheels if you want a nice ride and best gas mileage. The 3.92 gears will cost you about 2 mpg hiway.

I second the 22" wheels. My 20" wheels are a bit bumpy but that what came on it so I won't swap them. I remember noticing a big difference on my Chevy's when I went from 17" to 20's. I also put on a pair on Timber Grove ASAM's to correct the dreaded rear sag but my tongue weight will be far more that you boat trailer. I will be pulling a 25' Toy hauler that when fully loaded with be about 7K which should be fine. My 19 is rated at about 10K max for towing.
Make sure you get the class 4 hitch in case you do want to pull something heavier.
 

Mcjama76

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Did a trip last year, Oregon to Colorado Springs and back through Vegas. 3.92 gears on 20" tires. Depending on the stretch of road and elevation +/-, think the highest MPG between fuel stops was just shy of 24. Was trying to maximize mileage but this was done at or slightly above all posted speed limits.

upload_2021-3-1_11-16-33.png
 

runamuck

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Jim2015 the 3.21 will not have a lower first gear ratio as the 8 speed trans has the same first gear for all the various rear ends offered. 4.71 x 3.21 is not lower than 4.71 x 3.92 ..it's the other way around.
 
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