Rear axle ratio vs mpg.

[desdave37]

2021 1500 etorque hemi 4x4 3.92 axle. If I swapped to 3.23 what Change in mpg might I expect? What is a ballpark on having that work done? Also, as 4x4 is there any corresponding change to the front drive? Appreciate any info.

 

[Wild one]

Yes you'd have to swap the front to a 3.21 to.There won't be enough gain in milege to ever pay for the gear change. Unless you found somebody to swap diffs with,and they gave you a few bucks on top,and you swapped the housings yourself. Then you'd be ahead of the game and it'd be worth it,but if you're paying somebody to swap diffs,or install gears in the rear one,and swap the front diff,no you'll never get your money back. The front diff is a complete swap,as you can't change the gears in the front end.
You are sitting on the diffs alot of guys do want though,so finding somebody willing to swap your complete 3.92's for their 3.21's won't be hard to do.If you go that way,you could even ask for money on top.
Another option to look into would be swapping in 3.55's,they're a good middle of the road gear set between the 3.21's and 3.92's

 

[Yardbird]

I have a 3.21. You will never be able to use 8th gear under 75+ mph on any kind of rolling terrain. Even then you will shift down on most any kind of uphill rise.

I just lock out 8th to keep if from shifting downhill, them back again on level ground.

I do have 20" tires, so that would contribute to the excessive shifting compared to smaller around tires.

Ram should have put a 3.42 ratio in so 8th can be used like it should at 70-75 MPH.

 

[IDSandman]

Leave the 3.92 in. Much better ratio then the 3.21 imo. The fuel mileage difference is not enough to
Offset the cost plus it’s a truck and 1-2mpg shouldn’t matter.

 

[Wild one]

I have a 3.21. You will never be able to use 8th gear under 75+ mph on any kind of rolling terrain. Even then you will shift down on most any kind of uphill rise.

I just lock out 8th to keep if from shifting downhill, them back again on level ground.

I do have 20" tires, so that would contribute to the excessive shifting compared to smaller around tires.

Ram should have put a 3.42 ratio in so 8th can be used like it should at 70-75 MPH.

They should of kept the 3.55's with the 8 speed.When they first brought out the 8 speed in 2013,you could get a Hemi / 8 speed combo with the 3.55's,then they dropped that option in 2014. I think that was a mistake,but corporations don't listen to their consumers anymore,

 

[GTyankee]

It seems to me,
that when Chrysler was running the show ..

Ram was a masculine truck, if you saw a woman driving a Ram, you knew she could ride a horse an was not afraid of cleaning out the stalls, she could shoot pool & will drink a beer.

When FCA took over, security went out the door, Ram was more like a 40 year old ladies truck, she was just happy to get out of the family van.

Stellantis held Focus Groups & locked out masculinity

 

[CraigS41]

I had a 2019 Bighorn Classic with the 3.21, Now a 22 Laramie with the 3.92. In 8th gear at 55 mph, the 3.21 is running at 1250 RPM, the 3.92 is at 1500. The mileage difference is 20.5 with 3.21, and 19.0 with the 3.92. Same commute, 55 miles each way, over a 3200 foot mountain, down to 2000 feet, then back ove3r the mountain and down to 500 foot at home. I use the cruise control 90% of the time

 

[brian42]

Your driving habits and environmental conditions play more of a part in your fuel economy than gearing between 3.92 and 3.21.

I had a 2019 HEMI 4x4 and got about 15 mpg overall with my 3.21 (a little more with summer blend and a little less with winter blend).

 

[TestPilot57]

I do have 20" tires, so that would contribute to the excessive shifting compared to smaller around tires.

A point of clarification - they aren't 20" tires vs 18" tires, it's the rim/wheel diameter. Trucks from the factory with 20" rims have tires with a smaller sidewall, so the outside/rolling diameter remains the same (or close enough to make no difference).

 

[Yardbird]

A point of clarification - they aren't 20" tires vs 18" tires, it's the rim/wheel diameter. Trucks from the factory with 20" rims have tires with a smaller sidewall, so the outside/rolling diameter remains the same (or close enough to make no difference).

I haven't measured the height or circumfrence between the tires. I've just went by how each look in the fender wells.

 

[Yardbird]

I had a 2019 Bighorn Classic with the 3.21, Now a 22 Laramie with the 3.92. In 8th gear at 55 mph, the 3.21 is running at 1250 RPM, the 3.92 is at 1500. The mileage difference is 20.5 with 3.21, and 19.0 with the 3.92. Same commute, 55 miles each way, over a 3200 foot mountain, down to 2000 feet, then back ove3r the mountain and down to 500 foot at home. I use the cruise control 90% of the time

Dang, 1250 rpm. The V-6 will change with most any amount of throttle pressure at 1900 and under. It's rare on level ground to get down to 1500.

 

[ramffml]

I have a 3.21. You will never be able to use 8th gear under 75+ mph on any kind of rolling terrain. Even then you will shift down on most any kind of uphill rise.

I just lock out 8th to keep if from shifting downhill, them back again on level ground.

I do have 20" tires, so that would contribute to the excessive shifting compared to smaller around tires.

Ram should have put a 3.42 ratio in so 8th can be used like it should at 70-75 MPH.

As a counterpoint: my truck lives in 8th gear (literally). I bet 95% of its life is 8th gear, and yes that includes many hours of "rolling terrain". I'm also on 20 inch rims (stock diameter though).

Downshifting is not some boogyman either, it's a seamless 400 rpm increase and if you have tunes on or you're talking in a conversion its completely unnoticeable. The point of having all these gears, is to use them at times likes this. The truck always has a gear that makes the most sense, who cares if it drops a gear? That's why you have 8 of them.

And don't forget, when you're in the city: the 3.92 usually creates 1 extra upshift/downshift vs the 3.21, it uses more gears to get to the same speed. So if you're THAT concerned about shifting, then be honest and mention that the 3.92 is definitely more busy in the city.

Pick your poison.

For me, nothing better than cruising on the freeway at 1400 to 1500 RPMs for hours at a time, the truck is just idling its way through life with minimal drama.

Though I absolutely agree that the time for the 3.21 is when you're buying the truck, probably too late at this point unless the truck is brand new and you plan to drive the wheels off it.

Edit: ok I just realized you have the 3.6 with the 3.21. Completely different story, I know nothing about how that drive train feels. The hemi/3.21 is glorious though, no complaints. The OP drives a hemi, not the 3.6.

 

[Kickboxer]

Your driving habits and environmental conditions play more of a part in your fuel economy than gearing between 3.92 and 3.21.

I had a 2019 HEMI 4x4 and got about 15 mpg overall with my 3.21 (a little more with summer blend and a little less with winter blend).

Well said, it is much more how you drive than what gearing you have..
That said the 3.21 will offer better MPG...for most. That is what I have
and I really like it.

 

[GTyankee]

Something that i have noticed..
Ram 1500s that have 20" wheels, are the trucks that have the 1" Raised Ride Height.

17" & 18" wheeled Ram 1500s, when they leave the assembly plant, do not have it

 

[Wild one]

Something that i have noticed..
Ram 1500s that have 20" wheels, are the trucks that have the 1" Raised Ride Height.

17" & 18" wheeled Ram 1500s, when they leave the assembly plant, do not have it

The 17's on the 1500's are a 31" tall tire,the 20's on the 1500's are a 33" tall tire,differance divided by 2 = 1" raised ride height

 

[danielmid]

The 17's on the 1500's are a 31" tall tire,the 20's on the 1500's are a 33" tall tire,differance divided by 2 = 1" raised ride height

I checked and that math works out

 

[GTyankee]

That is where i messed up my life

I opted out of high school math
if it did not have a
- + ÷ ×
no fractions, percentages, etc., etc.
I can't work with a calculator either

no math & can't dance
if i could not use my hands to do the basic things, i would still be a Stock Boy in a Dress Shop, i delivered stock between stores

 

[Wild one]

That is where i messed up my life

I opted out of high school math
if it did not have a
- + ÷ ×
no fractions, percentages, etc., etc.
I can't work with a calculator either

no math & can't dance
if i could not use my hands to do the basic things, i would still be a Stock Boy in a Dress Shop, i delivered stock between stores

I loved math in school,it was english that buggered me up,i can't sound out a word for the life of me,i spell by memory,lol

 

[GTyankee]

LOL
I paid real good attention to final year High School English

she wore plaid skirts that touched her knee caps
she had a real nice profile
she had recently graduated from college, she was a substitute teacher

she passed me because i was very attentive

I never cared to study & could not wait to get out of school

Joined the Navy & went to boot camp, had to study, graduated
then they sent me to Aviation Ordnance "A" School in Jacksonville Florida, where i learned to handle Explosives, bombs, missiles, rockets, 20 mm ammo, etc. For that Class, i really paid attention

 

[Randy Grant]

It seems to me,
that when Chrysler was running the show ..

Ram was a masculine truck, if you saw a woman driving a Ram, you knew she could ride a horse an was not afraid of cleaning out the stalls, she could shoot pool & will drink a beer.

When FCA took over, security went out the door, Ram was more like a 40 year old ladies truck, she was just happy to get out of the family van.

Stellantis held Focus Groups & locked out masculinity

I guess that shows what you think of us all, including yourself