3.21. vs 3.92 gear

[Gman]

I wouldn't worry about it.

 

[riccnick]

I recently purchased a crewcab 4x4 hemi with the 3.21. If I am going to be towing an ultra-lite or lite travel trailer between 4500 and 7000 lbs., do I need to worry either way since it is under the 8000 limit for the 3.21?

What's your payload sticker say on the door jamb? You can use that to calculate your trucks EXACT towing capacity.

I also have a crew cab, 4x4 hemi truck with the 3.21. My (and your) GVWR is 7,100, my (and your) GCVWR is 13,900, and my (not your) payload sticker says 1,451 lbs.

Take GVWR and subtract Payload, and you get your Curb Weight (Mine is 7,100-1,451 = 5,649)
Take GCVWR and subtract Curb Weight and you get your Towing Capacity. (Mine is 13,900 - 5,649 = 8,251)

Now, it's important to remember that THIS method of calculating your Towing Capacity does not include any occupant weight, including yours as the driver, nor does it include any hitch weight or hitch equipment weight, so you must also subtract accordingly. For me it breaks down as follows:

If I'm in the truck, it's another 230 lbs off the top. (I have to be in the truck to drive it, as far as I know...)
I usually have about 200 lbs of tools and gear in the truck at all time.
And my hitch probably weighs close to 30 lbs, just by itself. No WD bars, just a draw bar with plate rated for 13,000 lbs with a 2-5/16" ball.

8,251 - 230 - 200 - 30 = 7,791 actual every day Towing Capacity for my truck with me and my gear in it.

If anyone else reading this wants to do the same math for a 3.92 truck, just simply replace the GCVWR of 13,900 with 17,000 lbs
If anyone else reading this want's to do the same math for a 2wd crew cab truck, simply replace the GVWR of 7,100 with 6,900 lbs.

The most important part of this is knowing what your payload sticker says, and knowing the weight of occupants, equipment, gear, and anything else in the truck.

 

[Willwork4truck]

I recently purchased a crewcab 4x4 hemi with the 3.21. If I am going to be towing an ultra-lite or lite travel trailer between 4500 and 7000 lbs., do I need to worry either way since it is under the 8000 limit for the 3.21?

No, I dont think you will have an issue. Lock out 8th gear perhaps. Read some of the towing threads for more up to date info, I don’t tow anymore.

 

[ColoradoCub]

I’ve got the 3.92’s and maybe I’m just lucky, I just rolled over 1000 miles on my truck and my lieometer says I’ve averaged 18.2 mpg over 1000 miles. That’s idling,city driving and some highway. That’s better than I expected. I have a travel trailer and I live in the Rockies so the 3.92’s were a no brainer for me.

 

[Nightmare90gt]

I went with 3.92 for the towing and not knowing were I will get stationed at next. Could be flat land or hills who knows.

 

[Dodgehemi0]

Not getting anything near that on mine...

Just took a trip from FL to WI
75mph and cruise control, 87 octane
15 mpg was average
14 mpg was worst tank
16 mpg was best tank

Have to add up the info for the ride back..

Yea I call total BS on a Rebal getting 18 city. Some people live in lala land.


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[Willwork4truck]

I went with 3.92 for the towing and not knowing were I will get stationed at next. Could be flat land or hills who knows.

Not a bad chouce. If I were to tow more than an ultralight rv less than 22’, a bass boat/jet ski I’d have taken the 3.92 gears. As it is, the 3.21’s do fine in hills. If I wete back living in the Rockies, then 3.92.

I still feel that dropping the 3.55’s in the Hemi was a mistake.

 

[NordicNevs]

3.73 standard just sayin

Hemi still has the 3.92 sitting on the floor in the box. Need to get the front somehow before I do the gear swap.


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[Maddoggin]

Can anyone post what the rpms are at 70mph with 3.21 and 3.92? I have a Laramie with 3.92 and get around 2000 or 2100 rpms at 70mph. Curious to hear what rpms the 3.21 is at 70mph!

With 8 spd transmission

 

[kittyjo]

Can anyone post what the rpms are at 70mph with 3.21 and 3.92? I have a Laramie with 3.92 and get around 2000 or 2100 rpms at 70mph. Curious to hear what rpms the 3.21 is at 70mph!

With 8 spd transmission

Roughly 1500 to 1600... 19.5mpg flat cruising speed. 80mph 1900rpm and 18.5mpg

 

[Firebird]

Can anyone post what the rpms are at 70mph with 3.21 and 3.92? I have a Laramie with 3.92 and get around 2000 or 2100 rpms at 70mph. Curious to hear what rpms the 3.21 is at 70mph!

With 8 spd transmission

I’m exactly 2000 rpm’s at 70

 

[Maddoggin]

I’m exactly 2000 rpm’s at 70

3.92 or 3.21?

 

[Maddoggin]

Roughly 1500 to 1600... 19.5mpg flat cruising speed. 80mph 1900rpm and 18.5mpg

3.92 or 3.21?

 

[Blueraptor]

I have 3.92 and at 70 mph I see just under 2000 rpm.

 

[DavidNJ]

The 8-speed transmission has a 4.71 first gear and a .67 eighth. With a 3.21 rear, the overall ratio in first is 15.1. GCWR with the 3.21 is 13,900. With the 3.92 it is 17,000#. With a 32" or 33" tire

In 2018 the Ram 2500 came with the same engine. With a 6-speed automatic, first was 3.23, the rear gear was 3.73, and the GCWR was 18,300#.

It is inconceivable that the axle ratio would have an effect in towing a 4k lb trailer with OE sized tires. However, top gear in the transmission is the same, so at highway speeds on level ground when the transmission is in 8th it will buzz the engine faster. Eighth with 3.92 is very close to 7th with the 3.21.

 

[SpeedyV]

3.92 or 3.21?

3.92 is in his signature.

 

[Firebird]

3.92 or 3.21?

3.92

 

[Maddoggin]

3.92 is in his signature.

Do you have bigger tires? I have stock 20 inch rims and tires and I'm getting right around 2000 rpms at 70mph

 

[SpeedyV]

Do you have bigger tires? I have stock 20 inch rims and tires and I'm getting right around 2000 rpms at 70mph

I think you meant to direct that response to @Firebird.

 

[Firebird]

I have the 22's, but the diameter is the same as the 20's since I have 45 series tires now