3:21 rear vs 3:92 gas mileage?

[jwaked]

My Limited had 3:21 and was fine, my Rebel with 3:92 and bigger gas tank not so good on MPG

 

[DA Smith]

My 2019 fifth gen Laramie 4x4 with 3.92 gears gets between 12 to 14 in town depending on how I drive it. On the highway the best I have ever got is 19 but I wanted the 3.92 for towing my 34 foot TT. When towing a load the 3.92 does definitely make a difference over the 3.21 on take off and on the highway at causing speed with the trailer. If you are not going to pull a heavy trailer and just plan on normal driving you will probably get around 3 mpg better on the highway with the 3.21 gears.

 

[suicideking]

My Limited had 3:21 and was fine, my Rebel with 3:92 and bigger gas tank not so good on MPG

The Rebel tires are 33" and most others are 32". So that extra inch is going to make your gas mileage a little worse too.

 

[Ramregret]

The biggest gain you'd see from having the 3.92 gear is starting from a dead stop, especially if towing moderate to heavy. And the biggest gain you'd see from the 3.21 is in 8th gear as @ramffml said already. People argue over which is better, but having owned both I can say that I wouldn't know which one I have if my window sticker didn't tell me LOL. Maybe if I towed or drove faster than 65 mph on a regular basis. Speed limits are low around here

Speed limits are just suggestions.

 

[Dusty]

My Limited had 3:21 and was fine, my Rebel with 3:92 and bigger gas tank not so good on MPG

Tires can make significant difference.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 105505 miles.

 

[ppine]

For a truck you are much better off with 3.92s.
My first 1/2 ton truck was back in the 1970s. It was great except it came with 3.07 gears. Even pulling a 2 horse trailer was hard on the clutch. I sold it and never bought another Chevy again.

Find some good charts. You can adjust your amount of rpms by changing the diameter of your tires.

 

[MD Sledhead]

My 2019 fifth gen Laramie 4x4 with 3.92 gears gets between 12 to 14 in town depending on how I drive it. On the highway the best I have ever got is 19 but I wanted the 3.92 for towing my 34 foot TT. When towing a load the 3.92 does definitely make a difference over the 3.21 on take off and on the highway at causing speed with the trailer. If you are not going to pull a heavy trailer and just plan on normal driving you will probably get around 3 mpg better on the highway with the 3.21 gears.

I agree 100%. I live in the mountains (of the Eastern US) Any time you get over 70 mph running 3.92s the mpg's start to drop. 75-80 mph is a huge difference versus the 3.21. If I didn't pull a larger trailer, I would have the 3.21s no question.
Now if you're running 2-lane 55-60 or so, you'll barely notice a difference.

With 3.92s the last 10+ years, I have only ever seen 19 mpg ONCE. That's when i purposely drove around 70-72 mph on relatively level ground. Mine usually lives around 15-16 mpg. (this is a Crew Cab 4x4 with 6'4" bed)

 

[Aircommuter]

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.

 

[mikeru]

Speed limits are just suggestions.

Maybe where you live. The law takes them seriously here. I go 4-5 mph over the posted speed limit. More than that and I'm tempting fate LOL.

 

[nonbonum]

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.

 

[Tulecreeper]

Maybe where you live. The law takes them seriously here. I go 4-5 mph over the posted speed limit. More than that and I'm tempting fate LOL.

I'll do 5 over all the time. Much faster than that and I start to stand out from the crowd and that is what gets you pulled over. Occasionally, I get caught in a group of vehicles that all want to do 70 in a 55 and I have to scoot along with them before I can get over and let those idiots pass.

 

[David James]

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!

Have a 2016 1500 Big Horn 4x4, crew cab with 20” wheels, and a slightly taller than cab high Lear topper, 3.21 rear end. Before topper averaged a shade over 20 mpg in my mostly highway driving, with best at 23.5 mpg from El Paso to central VA driving at about 72-73 mph cruise. The topper has cut my mpg by about a mile per gallon (5%) but I still get about 21-22 on the road at consistent highway speeds. Very quiet. Local mpg is 15-16. Great truck. I don’t tow as a routine but have pulled a ton weighted uhaul trailer once with truck also loaded with stuff and still got about 19 mpg - Lear cap may actually have helped in this case, and I held my speed to 65 mph. Hope this helps. I think you should shop for the best available truck first, and axle ratio is secondary.

 

[suicideking]

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.

Yes, looking up the VIN will show your axle ratio. Add your VIN at the end of the link below, it will pull up your sticker.

https://www.chrysler.com/hostd/windowsticker/getWindowStickerPdf.do?vin=

 

[1 MEAN66]

We have a 2016 Tradesman, I have the, 5.7, 6 spd. auto and 3.55's. I can actually get into 6th at 45mph, some of the 8 spd. you must bet at 60 or better to see 8th gear. have averaged 17.2-17.5 on every tank full. We took it on vacation ( 9 days) and averaged 21.5 for the entire trip ( stop & Go, interstate, local short trips, and sight seeing in the Susquehannock State Forest roads of Potter County PA,).But I am always using the "cruise"! when I leave a stop light, get to 20mph hit the cruise, etc. I think using the cruise makes the biggest difference. I tried two tanks of no cruse and averaged a more common 15.5 -16.5 per tank.

 

[Tulecreeper]

We have a 2016 Tradesman, I have the, 5.7, 6 spd. auto and 3.55's. I can actually get into 6th at 45mph, some of the 8 spd. you must bet at 60 or better to see 8th gear. have averaged 17.2-17.5 on every tank full. We took it on vacation ( 9 days) and averaged 21.5 for the entire trip ( stop & Go, interstate, local short trips, and sight seeing in the Susquehannock State Forest roads of Potter County PA,).But I am always using the "cruise"! when I leave a stop light, get to 20mph hit the cruise, etc. I think using the cruise makes the biggest difference. I tried two tanks of no cruse and averaged a more common 15.5 -16.5 per tank.

My 8-spd 2500 won't hit 8th until almost 65.

 

[dek1581]

We have a 2016 Tradesman, I have the, 5.7, 6 spd. auto and 3.55's. I can actually get into 6th at 45mph, some of the 8 spd. you must bet at 60 or better to see 8th gear. have averaged 17.2-17.5 on every tank full. We took it on vacation ( 9 days) and averaged 21.5 for the entire trip ( stop & Go, interstate, local short trips, and sight seeing in the Susquehannock State Forest roads of Potter County PA,).But I am always using the "cruise"! when I leave a stop light, get to 20mph hit the cruise, etc. I think using the cruise makes the biggest difference. I tried two tanks of no cruse and averaged a more common 15.5 -16.5 per tank.

On a side note: I also have 2017 Ram 1500 4WD BigHorn 3.21 rear/8 spd tranny. How fast will I actually have to go to be in 8th gear?

 

[Wild one]

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.

I did that exact scenerio,and the deeper gears take a big hit on milege at 70+ mph,plus oil temps increase by a significant amount.I never noticed any differance in holdback going downhill,plus i didn't notice any differance in the downshifts on hills unless the hill was above a 4% grade,then the 3.21's "might" downshift a bit quicker at 60 mph,but at 70+ mph there was no differance.On the freeway at 75+ mph,the 3.21's are way better on milege,and oil temps.

 

[Wild one]

On a side note: I also have 2017 Ram 1500 4WD BigHorn 3.21 rear/8 spd tranny. How fast will I actually have to go to be in 8th gear?

Right conditions,which means a light foot,my truck when it had 3.21's would go into 8th gear at 50 mph,but you have to know how to drive for milege for it to happen

 

[nonbonum]

Window sticker doesn't show axle ratio.
But I did find a link in an earlier post on the forum that provides the full equipment list via VIN.
Put your VIN in the window on this link. https://fcacommunity.force.com/RAM/s/equipment-listing

 

[mikeru]

I did that exact scenerio,and the deeper gears take a big hit on milege at 70+ mph,plus oil temps increase by a significant amount.I never noticed any differance in holdback going downhill,plus i didn't notice any differance in the downshifts on hills unless the hill was above a 4% grade,then the 3.21's "might" downshift a bit quicker at 60 mph,but at 70+ mph there was no differance.On the freeway at 75+ mph,the 3.21's are way better on milege,and oil temps.

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