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.