3:21 rear vs 3:92 gas mileage?

[ramffml]

Highway cruise mileage on my 3.92 limited is 20-21. The 3.21 will need to shift more since the 8sp has two overdrive gears. The 3.92 just keeps pulling up those hills. The only way to compare is to change the gears in the same truck driving the same course with the same driver over several weeks to account for different wind and traffic conditions. The 3.92 also provides better holdback downhills.

Both trucks have 2 overdrive gears.

The better way to look at this, is:
8th gear in the 3.92 = 7th gear in the 3.21
7th gear in the 3.92 = 6th gear in the 3.21

Whatever the 3.92 does in 8th, it will be 100% identical to the 3.21 in 7th. But the 3.21 has an extra upshift left and so it will drop 400 RPMs at that point.

Naturally if you come up to a grade and both trucks are in 8th, the 3.21 will be 400 rpms lower so it absolutely will downshift to match the 3.92. And then they're equivalent and both trucks might need to downshift again if needed.

The point of overdrive gears is to use them. I like how my truck basically idles through life. Downshifts are smooth and seamless, its not something I even notice if the tunes are on or I'm talking in the cab etc.

So no, the 3.92 will not pull better up hills nor will it provide more holdback. It just means the 3.21 has one extra gear to up/downshift first but: if the RPMs are identical in both trucks, they have identical performance.

 

[Wild one]

Meh...who cares about holdback when you have ACC?

I don't why this popped into my mind Mike,but that made me think of the old saying "brakes we don't need no stinking brakes"

 

[Wild one]

Both trucks have 2 overdrive gears.

The better way to look at this, is:
8th gear in the 3.92 = 7th gear in the 3.21
7th gear in the 3.92 = 6th gear in the 3.21

Whatever the 3.92 does in 8th, it will be 100% identical to the 3.21 in 7th. But the 3.21 has an extra upshift left and so it will drop 400 RPMs at that point.

Naturally if you come up to a grade and both trucks are in 8th, the 3.21 will be 400 rpms lower so it absolutely will downshift to match the 3.92. And then they're equivalent and both trucks might need to downshift again if needed.

The point of overdrive gears is to use them. I like how my truck basically idles through life. Downshifts are smooth and seamless, its not something I even notice if the tunes are on or I'm talking in the cab etc.

So no, the 3.92 will not pull better up hills nor will it provide more holdback. It just means the 3.21 has one extra gear to up/downshift first but: if the RPMs are identical in both trucks, they have identical performance.

I've noticed alot of guys have no clue what "final drive ratio's" mean,and can't comprehend how a transmission and it's gear ratio's apply to the overall driveline ratio.They seem to miss the fact that once you're moving and the transmission has made a few shifts,both 3.21 and 3.92 have virtually identical final drive ratio's,until they hit 8th

 

[mikeru]

I don't why this popped into my mind Mike,but that made me think of the old saying "brakes we don't need no stinking brakes"

Haha I remember saying that to my brother when we were building a go-cart one time. Turns out I was wrong.

 

[CaptCurt]

Hello,

I am looking to purchase either a new 5.7L Laramie or Limited. The issue is that the Limiteds I am looking at all have the 3:92 rear end. My usage will be 99% city and highway with no towing(at present).

Can anyone share their knowledge on the significance as it relates to gas mileage?

Thanks for your help!

3.21 for sure, unless you're planning on towing or hauling heavy loads. Even with the 3.21s, you can still tow and haul if it's off and on with medium to light loads. And you should get 3-5 more MPG with them, vs the 3.92s.

 

[Wild one]

Haha I remember saying that to my brother when we were building a go-cart one time. Turns out I was wrong.

I know what you mean,lol.I built a go-cart in high school shop class,and i jumped on it before we had any brakes on it,big mistake,after i quit leaking blood,i brought it back into shop class and we put a basic drum brake on the back axle,lol

 

[Renegade17]

My 2 cents,
I had the 3.21 in my 2017 Longhorn crew cab 5.7 box, City driving is 10-12mpg, Highway driving is 14-16mpg at 55 mph , 11-13 at 70 mph. Towing 65 -67 mph 5,000lb trailer 8-10 mpg. Into the wind is more like 7-9 mpg range.

I now have a 2019 Warlock crew cab 5.7 box with 3.92. MPG overall is just about the same as the 3.21 in the city, But a louch when towing.
The 3.92 are great for off the line and passing when towing.
I have spent years towing and what i call hunting for what the best highway speed along the NYS thruway for the best MPG i can get.
Results 66-68 MPH range is it for my truck.
None of these trucks are ment for good gas milage but great for towing ! Oh I alos notice no diffrence in mpg when in tow mode but love how it downsifts as toy slow to a stop.

 

[suicideking]

I'm looking to buy a 1500, probably at the end of this year. Other than the Rebel (not into the red interior), the 3.92 gears seem pretty hard to find. I will tow eventually, so would prefer it. Though figure I will most likely end up with 3.21 just because of selection. I figure the 3.21 will be better for me, other than when I'm towing. Only plan to tow a few times per year.

There is one I like about an hour from me. Only thing I wouldn't have selected is it has the 6' 4" box instead of the 5' 7". Other than that, the closest one is 4 hours away. Also might buy a used one, selection is even slimmer then.

 

[Truckit]

I have driven almost a million kms on Hemi 1500s. Eight new ones starting in 2007. I have owned all 3 ratios and trasmissions. I only order 3:92s now because of towing capacity and drivability. Some 3:21s will tend to hunt for the proper gear at certain speeds depending on 5,6 or 8 speed. At steady 55 mph I found the 3:92s actually improve fuel mileage over the 3:21 or 3:55s. The difference is very little with an 8 speed. I have all my fuel records and could calculate it exactly but there really isn't enough difference to bother.

 

[Jim S]

I have a 2021 Laramie Sport with 5.7 e BS and 3.92. I continually average 17mpg per dashboard. Lot's of hwy miles SW Louisiana to Tampa 8 times plus DFW, ATL, HOU, etc. got 62K on it.
Just for fun, I slowed down to 60 for 20 miles (in a 60mph zone), got 28mpg indicated. Drove 70mph in a 70mph zone for 20 miles...got 21 mpg indicated
returned to my normal 80-85mph got 17mpg.

Hope that helps.

 

[Rado]

Reset the MPG read out on both and test drive both about 15/20 miles same road and speed if it would show much difference ??

 

[mikeru]

I'm looking to buy a 1500, probably at the end of this year. Other than the Rebel (not into the red interior), the 3.92 gears seem pretty hard to find. I will tow eventually, so would prefer it. Though figure I will most likely end up with 3.21 just because of selection. I figure the 3.21 will be better for me, other than when I'm towing. Only plan to tow a few times per year.

There is one I like about an hour from me. Only thing I wouldn't have selected is it has the 6' 4" box instead of the 5' 7". Other than that, the closest one is 4 hours away. Also might buy a used one, selection is even slimmer then.

If you are buying new and don't plan to buy till the end of the year you might consider placing an order. That way you can get the exact configuration you want. Just a thought.

 

[Wild one]

The 3.92 are great for passing when towing.

I don't think you understand "final drive ratio's" with that comment. If the truck downshifts to 6th with 3.92's while passing,it'll also downshift to 5th with 3.21's in the same scenerio,and there's no differance in the final drive ratio.The truck will downshift to it's sweet spot with both gear ratio's,just one will be in a lower gear,but their overall final drive ratio's will be the same.The 3.21's actually have the torque multiplication advantage after the 3.92's shift into 2nd,as the 3.21's will still be in 1st gear

 

[suicideking]

If you are buying new and don't plan to buy till the end of the year you might consider placing an order. That way you can get the exact configuration you want. Just a thought.

I have thought about that. Especially since this is the last year of this model with the 5.7. Next year will be an I6 Turbo like the Toyota and Ford EB. It will probably be fine, but I never like to buy 'first year' cars.

Anyone know what the deadline is to order a 2024?

 

[Marshall]

I have 3.92 gears and really like it, My last one was a 2010 Laramie, and I am not sure what was in that, different transmission. I get way better milage with the 8 spd and 3.92, and if you put your foot into it, way difference.
At 120km, 70mph I would think you could not tell what gears you had, with a trailer maybe.
I think the wind has way more to do with mileage on the HI way, I usually have that gauge on the dash highlighted.
Around town ,sitting at red lights , your gas mileage is not that great, no matter what gears you have.

Most of my towing was done back with 3 speed transmissions, or a 4 sp stick.

 

[Jerrybob]

2019 Tradesman crew cab.....5.7 Hemi....3.92 rear.....4x4....tow package......we live rural....two lane roads at 50 to 55mph mostly......I get 20 to 21 mpg almost always......I admit.....I don't have a heavy foot.......we tow a small travel trailer.....bout 4000lbs.....we consistently get 16 to 18 mpg when towing.....my truck doesn't know a trailer is back there.....even when towing through the Rockies.......I also tow a 17ft car trailer loaded with either carriages...wagons or my tractor......16 to 17 mpg always. Love the truck.....love the mileage.....3.92 for me!

 

[Neomoritate]

Just out of curiosity does the VIN indicate the axle ratio?

I have a 2020 1500 4x 5.7 hemi. Truck was originally titled in Canada.

Went to it from a 7.3 Power Stroke and find the RAM obviously less of a tow vehicle – disappointing acceleration when towing, even light trailers. But since I tow infrequently, I am otherwise very pleased with the RAM.

You can get your truck's Build Sheet here:

FCA RAM

fcagroup.my.site.com

 

[Aircommuter]

Both trucks have 2 overdrive gears.

The better way to look at this, is:
8th gear in the 3.92 = 7th gear in the 3.21
7th gear in the 3.92 = 6th gear in the 3.21

Whatever the 3.92 does in 8th, it will be 100% identical to the 3.21 in 7th. But the 3.21 has an extra upshift left and so it will drop 400 RPMs at that point.

Naturally if you come up to a grade and both trucks are in 8th, the 3.21 will be 400 rpms lower so it absolutely will downshift to match the 3.92. And then they're equivalent and both trucks might need to downshift again if needed.

The point of overdrive gears is to use them. I like how my truck basically idles through life. Downshifts are smooth and seamless, its not something I even notice if the tunes are on or I'm talking in the cab etc.

So no, the 3.92 will not pull better up hills nor will it provide more holdback. It just means the 3.21 has one extra gear to up/downshift first but: if the RPMs are identical in both trucks, they have identical performance.

What about first gear? Same. Plus the 3.92 truck can pull better with less shifting. The ratios don’t equal out in every gear.

 

[ramffml]

What about first gear? Same. Plus the 3.92 truck can pull better with less shifting.

No, the same final gear ratios are available other than 1st in the 3.92 and 8th in the 3.21. If you're towing in the city or the freeway both trucks will shift identically.

The ratios don’t equal out in every gear.

What matters is final gear ratio (transmission * rear axle). Those do approximately equal other than the exceptions mentioned above.

 

[Wire4money]

I have thought about that. Especially since this is the last year of this model with the 5.7. Next year will be an I6 Turbo like the Toyota and Ford EB. It will probably be fine, but I never like to buy 'first year' cars.

Anyone know what the deadline is to order a 2024?

I don’t think they are making them anymore. I think 2025 production has started.