3.55 vs 3.92

[tobyd]

The 3.92 axle ratio is actually better on fuel for city driving, less effort to go from stop to city driving speed.
The 3.21 gets better highway mpg.

Huh, I never would have guessed that. And I'd be guessing -- I just assumed the longer ratio rear end would have had better mileage in all conditions.

 

[SpeedyV]

The 3.92 axle ratio is actually better on fuel for city driving, less effort to go from stop to city driving speed.
The 3.21 gets better highway mpg.

I raise an eyebrow at this. My city economy is poor, and I'm generally easy on the throttle. I'd be surprised if the 3.21 is poorer. But I could see vehicle weight (i.e. options) and driver aggressiveness having more impact than gearing in town.

 

[PowerJrod]

This comes up every so often, the 3.55 is only with the v6.

But even if it was available I'd say it's a poor choice for the Hemi + 8 speed. It would neither give you that much better towing nor that much better mpg, kind of pointless. Just pick the 3.21 or 3.92 based on your priority; the one maximizes mpg while still giving you everything you need to pull within realisitic payloads, and the other maximizes towing while at the expense of some highway MPG. I see no point in going half way in between and gaining neither one or the other.

I have to disagree my friend. Having an axle ratio that has a good blend of each is something that almost every serious truck driver would appreciate. To say you need one or the other and not having a happy medium comprise is like saying you have to choose between reliability and comfort/enjoyment. Personally I came close to buying a 2020 F150 with a 3.55 but got too good of a deal on my RAM to pass up.

 

[PowerJrod]

3.21 here. As bad as my city MPG is (due to stupid-short commute) I can’t imagine what I would get with a 3.92.

I already get around ~9-10 MPG as it is. And if I do one or two 20-mile highway drives on weekends, then it goes up to around 12 MPG.

That's not great for a 3.21. with my Etorque 3.21 I get 23-24mpg highway pretty consistently.

 

[Neurobit]

That's not great for a 3.21. with my Etorque 3.21 I get 23-24mpg highway pretty consistently.

I can too if I keep it at 60 MPH. At 75+, I’ve never been able to get above 19.7, hand calculated.

 

[neeginan]

Get the 3.92 and reduce it with larger diameter tires.

Tire Size Change Gear Ratio Calculator | Interco Tire

Calculate the proper gear ratio for a tire size change.

www.intercotire.com

Assuming stock tire size of 275 55 R20 (or another ~32 in tire):

If you have a 3.92 and go with 275 65 R20 tires, you will reduce your 3.92 to effectively a ~ 3.67.

If you have a 3.92 and go with 275 70 R20 tires, you will reduce your 3.92 to effectively a ~3.55.

 

[PowerJrod]

I can too if I keep it at 60 MPH. At 75+, I’ve never been able to get above 19.7, hand calculated.

Oh lol. Yea over 75mph my MPGs go down to that too, but if I stay under 70mph I'll still get well over 20mpg.