An Engineer's Ultimate Guide To 3.21 VS 3.92 Axle Ratio

[Usmc041127]

My limited with 4x4 off road package was ordered with the 3.92. I love the truck and still getting use to it at 600 miles now. I run it in aero mode. I am a bit disappointed in the 3.92. I live in the Midwest and it downshifts on most inclines on the highway. I haven't towed anything with it yet and I set the cruise at 60. Perhaps its just not broke in but I am only getting 15.2 mpg via the computer. My 13.5k lbs ram 5500 with 4.44 gears if i am not mistaken is averaging 12.3 and thats towing and normal driving. But it is also a 6.7 diesel and 77k miles. I was expecting my limited to tackle the hills a little better than it does empty with the 3.92. I cannot compare it to the 3.21 as I have never driven one. Just my .2 cents. For me I think if I was to do it over I would probably give the 3.21 a try. Just to see the difference on the highway mostly.

 

[HSKR R/T]

My limited with 4x4 off road package was ordered with the 3.92. I love the truck and still getting use to it at 600 miles now. I run it in aero mode. I am a bit disappointed in the 3.92. I live in the Midwest and it downshifts on most inclines on the highway. I haven't towed anything with it yet and I set the cruise at 60. Perhaps its just not broke in but I am only getting 15.2 mpg via the computer. My 13.5k lbs ram 5500 with 4.44 gears if i am not mistaken is averaging 12.3 and thats towing and normal driving. But it is also a 6.7 diesel and 77k miles. I was expecting my limited to tackle the hills a little better than it does empty with the 3.92. I cannot compare it to the 3.21 as I have never driven one. Just my .2 cents. For me I think if I was to do it over I would probably give the 3.21 a try. Just to see the difference on the highway mostly.

If you 3.92 truck is downshifting one gear, a 3.21 truck would more than likely be making two downshifts. Also, every gear above 6th is an "overdrive". You can use gear limiter to keep it in 7th and it wouldn't shift down on hills.

 

[Usmc041127]

If you 3.92 truck is downshifting one gear, a 3.21 truck would more than likely be making two downshifts. Also, every gear above 6th is an "overdrive". You can use gear limiter to keep it in 7th and it wouldn't shift down on hills.

Do they get a little better fuel mileage broke in more? Maybe at a different cruise speed? I know my wrecker 60 to 65 is the sweet spot.

 

[Ramjack]

Do they get a little better fuel mileage broke in more? Maybe at a different cruise speed? I know my wrecker 60 to 65 is the sweet spot.

No, not really. Kind of a myth these days. It applied several decades ago when engines came out of the factory with overly tight tolerances. 60-65mph should be a good range for highway MPG. Mine starts to take a dive at 75.

 

[BowDown]

Do they get a little better fuel mileage broke in more? Maybe at a different cruise speed? I know my wrecker 60 to 65 is the sweet spot.

I never noticed that, I've got the same mileage since day one.
I've read that on these modern engines that the bearings are broken in almost immediately and most ring manufacturers claim within 100 miles but recommend varying rpm.

IMO, what most people are seeing as far as fuel mileage improvement after break-in is the tune (fueling) actually changing.
GM has a 500 mile break-in tune for vehicles as I'm sure most OEMs do as well.

 

[BowDown]

No, not really. Kind of a myth these days. It applied several decades ago when engines came out of the factory with overly tight tolerances. 60-65mph should be a good range for highway MPG. Mine starts to take a dive above 75.

As does mine. 72-74 seems to be the sweet spot for around 22-24mpg. 65mph I can get 25-26 but I'm getting passed by everyone. 40-50 mph is crazy, I've seen 30mpg+ but those are short 4-6 mile stretches in town

 

[Mountain Whiskey]

My limited with 4x4 off road package was ordered with the 3.92. I love the truck and still getting use to it at 600 miles now. I run it in aero mode. I am a bit disappointed in the 3.92. I live in the Midwest and it downshifts on most inclines on the highway. I haven't towed anything with it yet and I set the cruise at 60. Perhaps its just not broke in but I am only getting 15.2 mpg via the computer. My 13.5k lbs ram 5500 with 4.44 gears if i am not mistaken is averaging 12.3 and thats towing and normal driving. But it is also a 6.7 diesel and 77k miles. I was expecting my limited to tackle the hills a little better than it does empty with the 3.92. I cannot compare it to the 3.21 as I have never driven one. Just my .2 cents. For me I think if I was to do it over I would probably give the 3.21 a try. Just to see the difference on the highway mostly.

At least you are not downshifting going downhill with a tailwind like you would be with Girly Gears.

 

[HSKR R/T]

I never noticed that, I've got the same mileage since day one.
I've read that on these modern engines that the bearings are broken in almost immediately and most ring manufacturers claim within 100 miles but recommend varying rpm.

IMO, what most people are seeing as far as fuel mileage improvement after break-in is the tune (fueling) actually changing.
GM has a 500 mile break-in tune for vehicles as I'm sure most OEMs do as well.

I'd say the "improvement" in fuel mileage comes.fdom the newness of the truck wearing off, especially the Hemi power, and they start driving more sensible.

 

[BowDown]

I'd say the "improvement" in fuel mileage comes.fdom the newness of the truck wearing off, especially the Hemi power, and they start driving more sensible.

That's entirely possible too, I know my yearly mileage has certainly slowed now that the newness is wearing off. I still enjoy driving the truck but I'm back to making efficient trips rather than driving because I want to drive the truck

 

[Ramroo]

Here is my take on the 3.92 vs 3.21 axle ratio. I own a 2021 1500 with 3.92 and a 2022 1500 with 3.21. My son drives the 21 with 3.92 so I can’t officially claim it now. They are close to the same trucks except the 3.21 truck is a long bed. I drove in town, cruised, hauled, and towed with the 3.92 for a year before my 3.21 truck came in from an order. I have now done the same with the 3.21 as far as driving in town, cruising, hauling and towing the same weights as well as empty. I am glad now that a ordered the 3.21 because I have not had any issues towing because the trans shifts so well, and tow / haul works. What really pisses me off about the 3.92 truck is it was turning 2100 to 2200 rpm at 75mph where the 3.21 truck is at 1750 rpm at 75mph ( empty trucks ). Not a big deal I guess, but it actually bothers me on long expressway cruising with the RPMs that high on the 3.92 truck. I’m sure the high and increasing gas prices and current people in charge doesn’t help my anxiety.
There are lots of strong opinions on the 3.92 vs 3.21 subject, but if someone is arguing the subject without owning and using both types of trucks, they really don’t have a dog in the fight.
Fights On

 

[SnowBlaZR2]

Here is my take on the 3.92 vs 3.21 axle ratio. I own a 2021 1500 with 3.92 and a 2022 1500 with 3.21. My son drives the 21 with 3.92 so I can’t officially claim it now. They are close to the same trucks except the 3.21 truck is a long bed. I drove in town, cruised, hauled, and towed with the 3.92 for a year before my 3.21 truck came in from an order. I have now done the same with the 3.21 as far as driving in town, cruising, hauling and towing the same weights as well as empty. I am glad now that a ordered the 3.21 because I have not had any issues towing because the trans shifts so well, and tow / haul works. What really pisses me off about the 3.92 truck is it was turning 2100 to 2200 rpm at 75mph where the 3.21 truck is at 1750 rpm at 75mph ( empty trucks ). Not a big deal I guess, but it actually bothers me on long expressway cruising with the RPMs that high on the 3.92 truck. I’m sure the high and increasing gas prices and current people in charge doesn’t help my anxiety.
There are lots of strong opinions on the 3.92 vs 3.21 subject, but if someone is arguing the subject without owning and using both types of trucks, they really don’t have a dog in the fight.
Fights On

I agree, the 3.21 is great if your main use for the truck is highway crusing at 75 mph on your way to get a mango frappe.

Just finished an 8 hour tow and was glad I went with the truck gears the whole way.

 

[Idahoktm]

Here is my take on the 3.92 vs 3.21 axle ratio. I own a 2021 1500 with 3.92 and a 2022 1500 with 3.21. My son drives the 21 with 3.92 so I can’t officially claim it now. They are close to the same trucks except the 3.21 truck is a long bed. I drove in town, cruised, hauled, and towed with the 3.92 for a year before my 3.21 truck came in from an order. I have now done the same with the 3.21 as far as driving in town, cruising, hauling and towing the same weights as well as empty. I am glad now that a ordered the 3.21 because I have not had any issues towing because the trans shifts so well, and tow / haul works. What really pisses me off about the 3.92 truck is it was turning 2100 to 2200 rpm at 75mph where the 3.21 truck is at 1750 rpm at 75mph ( empty trucks ). Not a big deal I guess, but it actually bothers me on long expressway cruising with the RPMs that high on the 3.92 truck. I’m sure the high and increasing gas prices and current people in charge doesn’t help my anxiety.
There are lots of strong opinions on the 3.92 vs 3.21 subject, but if someone is arguing the subject without owning and using both types of trucks, they really don’t have a dog in the fight.
Fights On

At 75 mph, my truck is turning 1900 rpm's. Not sure why yours is at 2100-2200 rpm's unless you installed smaller tires.

 

[Ramroo]

I agree, the 3.21 is great if your main use for the truck is highway crusing at 75 mph on your way to get a mango frappe.

Just finished an 8 hour tow and was glad I went with the truck gears the whole way.

Since you know what a frikin mango frappe is, tells me a lot. I don’t think I would like it, too much sugar.

 

[Ramroo]

At 75 mph, my truck is turning 1900 rpm's. Not sure why yours is at 2100-2200 rpm's unless you installed smaller tires.

Pic while cruising with stock laramie tires. Both trucks stock.

 

[Mountain Whiskey]

I agree, the 3.21 is great if your main use for the truck is highway crusing at 75 mph on your way to get a mango frappe.

Just finished an 8 hour tow and was glad I went with the truck gears the whole way.

Apparently the 3.21 driver may prefer the sugar free peppermint-sprinkle-mocha-nilla-grande-nitro-berry latte since the mango frame has too much sugar.

I'll take some "no label" #3 char barrel 2 year with a coke myself.

 

[Mountain Whiskey]

Pic while cruising with stock laramie tires. Both trucks stock.

Yea but they come with Prius tires on them. When you put truck tires on the 3.21 becomes the fail.

 

[Idahoktm]

Pic while cruising with stock laramie tires. Both trucks stock.

I'll have to take a pic of mine next time I'm on the freeway, for proof, but I know it's 1900 rpm's.

 

[BowDown]

I'll have to take a pic of mine next time I'm on the freeway, for proof, but I know it's 1900 rpm's.

At 75 MPH?

 

[Ramroo]

Apparently the 3.21 driver may prefer the sugar free peppermint-sprinkle-mocha-nilla-grande-nitro-berry latte since the mango frame has too much sugar.

I'll take some "no label" #3 char barrel 2 year with a coke myself.

Born and raised on 4 year old Jim Beam.
Since you drink whiskey with coke says it all!!!!

 

[Idahoktm]

At 75 MPH?

Yep.