3.21 vs 3.92: The Last Word

[SnowBlaZR2]

Oh, crap! I guess I should return mine?

Nah. Just learn from the mistake and get it right next time.

 

[Idahoktm]

These threads always go sideways. LOL.

On a serious note, I've driven both quite a bit. And I've got a buddy who leases a new Ram every couple of years and he's had both also. And I think we both agree that 3.21s feel very very different. Just got my new truck a few weeks ago with the 3.21s. Moderate acceleration feels like you could pitch a tent and roast some hotdogs. I've seen all the charts with gears matched to ratios and RPMs and all that. But at the end of the day the 3.21s just feel anemic and I haven't even hooked on the enclosed trailer yet. I also find it hard to believe that there's a 2 MPG loss on these trucks with the 3.92. My new 3.21 truck is only averaging 16 MPG. It won't even do window sticker. Sometimes I wonder if the 3.92s wouldn't actually be better around town because the gearing advantage means the accel pedal doesn't get used as hard. Hmm...

Oh well, I'm going to enjoy the truck anyway! But it'll be the last set of 3.21 "airplane gears" as my Dad calls them in my driveway.

A back-to-back test drive with 3.21's and 3.92's is what pushed me to order 3.92's. It wasn't a night and day difference, but it was definitely noticeable.

Combined fuel economy is a weighted average of city and highway MPG values that is calculated by weighting the city value by 55% and the highway value by 45%. My window sticker says my combined average should be 17 mpg. I get 16-16.5 without any highway driving and 17-17.5 with about 20% highway miles. That's using my onboard computer which is dead on balls accurate.

Does he call them airplane gears because of how slow jet engines spool up?

 

[Dewey]

Dang I shoulda got 3.92’s. Might have gotten a few more feet outa her.


Figured my rear wheel-wells needed some undercoating.

 

[StuartV]

Yep my dash is reading 17.5 right now. So realistically 16 to 16.5. My '20 was always reading high also. I wish these trucks had a diagnostic menu accessible on the dash where the MPG display could be calibrated like on the Ford trucks.

Maybe. I've had mine read high (over about 500 miles) by over 3 MPG. And I've had it read low by almost 1 MPG. But, usually it's about 1 .5 MPG high, roughly.

Unless you check it every time you fill up, you just don't really know.

 

[djevox]

Maybe. I've had mine read high (over about 500 miles) by over 3 MPG. And I've had it read low by almost 1 MPG. But, usually it's about 1 .5 MPG high, roughly.

Unless you check it every time you fill up, you just don't really know.

Must be those 3.21’s lying to the BCM. The 3.92’s always tell the truth…

 

[StuartV]

They are. But, fuel economy savings between either are negligible.

There's really no good reason to order a truck with 3.21s.

My Hemi w/eTorque and 3.92 got 14.1 MPG overall, and that was with a LOT of highway driving. It got around 12 (or less) strictly driving in town. Can't imagine how bad it would have been if it's worse with 3.21 gears.

Oh, except it's not. Just like everything else in your post was wrong.

Really, the only good reason to buy 3.92 gearing with a Hemi is if you tow at or near the limit of weight the truck is rated for AND you do a lot of that towing in stop-and-go traffic. If you really want to be going down the highway at 70MPH and turning 2000 RPMs, you can still do that with 3.21 gears. Just hit the little minus button on the steering wheel to lock out 8th gear.

 

[StuartV]

Must be those 3.21’s lying to the BCM. The 3.92’s always tell the truth…

It was the same in over 72K miles of experience with my last Hemi (with 3.92 gears)...

 

[SnowBlaZR2]

My Hemi w/eTorque and 3.92 got 14.1 MPG overall, and that was with a LOT of highway driving. It got around 12 (or less) strictly driving in town. Can't imagine how bad it would have been if it's worse with 3.21 gears.

Oh, except it's not. Just like everything else in your post was wrong.

Really, the only good reason to buy 3.92 gearing with a Hemi is if you tow at or near the limit of weight the truck is rated for AND you do a lot of that towing in stop-and-go traffic. If you really want to be going down the highway at 70MPH and turning 2000 RPMs, you can still do that with 3.21 gears. Just hit the little minus button on the steering wheel to lock out 8th gear.

Cool. I can do better than that towing my camper. So...sounds like gearing isn't the issue.

So, better fuel economy and much better towing performance, especially out west and in the rest of the real world. Guess I'll keep waiting for a good reason to get a weaker rear end.

 

[StuartV]

Cool. I can do better than that towing my camper. So...sounds like gearing isn't the issue.

So, better fuel economy and much better towing performance, especially out west and in the rest of the real world. Guess I'll keep waiting for a good reason to get a weaker rear end.

We both had/have 3.92 gears and you get better mileage than I did. Therefore, you get better than 3.21 gears would. Seems like solid logic, to me....

 

[SnowBlaZR2]

We both had/have 3.92 gears and you get better mileage than I did. Therefore, you get better than 3.21 gears would. Seems like solid logic, to me....

We don't even need to worry ourselves with logic. We have math, and the math is easy.

 

[theblet]

Cool. I can do better than that towing my camper. So...sounds like gearing isn't the issue.

So, better fuel economy and much better towing performance, especially out west and in the rest of the real world. Guess I'll keep waiting for a good reason to get a weaker rear end.

3.21 vs 3.92: The Last Word

 

[StuartV]

I traded my '19 with 3.92 for a '21 with 3.21 3 weeks ago.

So far, I've driven 3700 miles and my combined city/highway average is 24 MPG.

 

[SnowBlaZR2]

3.21 vs 3.92: The Last Word

We already squashed that with the numbers. No need to devolve to the before times.

 

[nc_beagle]

My 2013 Mazda shows my rolling average fuel economy but it also shows a rolling average MPH, which is kind of handy for seeing if I'm trending towards more city driving versus highway. When I first got the car we took it on longer trips and I think my average speed was about 35mph. Now its like 31-32mph on average and my mileage is down a little bit. Would be a handy feature to have on the truck and pretty simple to add to the system.

 

[StuartV]

My 2013 Mazda shows my rolling average fuel economy but it also shows a rolling average MPH, which is kind of handy for seeing if I'm trending towards more city driving versus highway. When I first got the car we took it on longer trips and I think my average speed was about 35mph. Now its like 31-32mph on average and my mileage is down a little bit. Would be a handy feature to have on the truck and pretty simple to add to the system.

You can already get to a display that shows total hours. Odometer tells you miles. Divide and have average speed.

 

[djevox]

It was the same in over 72K miles of experience with my last Hemi (with 3.92 gears)...

 

[SnowBlaZR2]

View attachment 136930

Only serious replies please. We MUST get to the bottom of this. I need to know if everyone else bought the right truck or not.

 

[J-Cooz]

Everybody takes this so personal.

My ecodiesel has 3.92s and gets 28+ MPG easily on the highway. I generally drive around 70mph, not much faster. If I lived in the USA where speed limits are 75+ (it's 62mph or 100kmh) in most of Ontario Canada, I'd probably get the 3.21.

Ideally the old 3.55 rear end would probably be ideal.

I do tow and I like the 3.92 combined with the ecodiesels torque. It gets heavy loads moving with very little effort.



Sent from my SM-G781W using Tapatalk

 

[Idahoktm]

Everybody takes this so personal.

Nope. Almost nobody is taking this seriously.

 

[theblet]

Everybody takes this so personal.

nah. I bought my truck because of the features and color, despite the rear end. i don't even GAF because I don't tow barely ever. these threads are very entertaining tho!