3.21. vs 3.92 gear

[Mike97]

I’m looking to place an order and I’m not sure of which gear ratio to order. 95% of the time I will be driving the truck empty. Gas mileage is important to me so I’m ordering the e-torque engine. I tow a small trailer that weighs 4000 lbs and only do it 6-8 weekends a year.

My concern is that the 3.92 gear is going to kill the gas mileage. The 3.21 just seems a bit low for a truck of this size.

Looking for the mpg difference between the two in every day driving.

Thanks

 

[bgmshrm]

I’m looking to place an order and I’m not sure of which gear ratio to order. 95% of the time I will be driving the truck empty. Gas mileage is important to me so I’m ordering the e-torque engine. I tow a small trailer that weighs 4000 lbs and only do it 6-8 weekends a year.

My concern is that the 3.92 gear is going to kill the gas mileage. The 3.21 just seems a bit low for a truck of this size.

Looking for the mpg difference between the two in every day driving.

Thanks

if you are leaving it stock height id get the 3.21s

 

[Mike97]

Good point about height. Yes I plan on leaving it stock with 20’s. It will also be a 4x4

 

[SuperShortMag]

Have nothing to back this up because only have owned the 3.92 gears, but I think it would depend a lot on where you live. My truck spends most of it's life on some pretty good size hills and back roads. My 3.92 gets better mileage when I average 60 on a 2 lane then it does at 70 on the interstate. Mind you we are only talking about 1 mpg or less most of the time. If I lived in flatter land or a lot of interstate driving, I would consider the 3.21

 

[19llhpb]

Wish a 3:55 would be available for all trim levels and engine options as it seems that would be a good fit for most guys.

 

[MrHankbot]

Have nothing to back this up because only have owned the 3.92 gears, but I think it would depend a lot on where you live. My truck spends most of it's life on some pretty good size hills and back roads. My 3.92 gets better mileage when I average 60 on a 2 lane then it does at 70 on the interstate. Mind you we are only talking about 1 mpg or less most of the time. If I lived in flatter land or a lot of interstate driving, I would consider the 3.21

The advice to go 3.21 if you live in flatter land or do a lot of interstate driving is good advice. At interstate speeds in NE (75-80) my truck gets 14-16mpg. At 65-70 it gets 17mpg, at 55-60 it gets over 18mpg. You can see how a taller gear would help if you did a lot of 60mph+ driving.

Oh, and at 85-90mph on the interstate with a strong diagonal headwind rushing to see my grandmother in the hospital it does about 11.5mpg.

 

[Mich thor]

With a 4 k trailer, I think the 3.21 would be the way to go. I had a hard time finding 3.92s. My camper is about 7 k and I think 3.21 would have handled it. In the city 3.92 is nice.Good Luck

 

[Mike97]

Wish a 3:55 would be available for all trims and models as it seems that would be a good fit for most guys

I agree 100% with the 3.55 gear.

My truck now is a Gmc 5.3 with a 3.77 gear. I get 18-20 with a combination city/hwy driving. Like one of the previous post stated it’s probab only 1 mpg between the 3.21/3.92. I live in Texas so it’s pretty flat but my towing trips are to Colorado and Utah so I’ll probably bite the bullet and go for the 3.92.

Thanks for all the advise.

 

[CCryder500]

With the 8-speed trans, first gear is pretty low, so the 3.21 should be fine. I have it in mine and it shifts out of first gear almost immediately, unless you really get on it. Should be perfect with a 4k lb trailer.

 

[th3duke]

I agree 100% with the 3.55 gear.

My truck now is a Gmc 5.3 with a 3.77 gear. I get 18-20 with a combination city/hwy driving. Like one of the previous post stated it’s probab only 1 mpg between the 3.21/3.92. I live in Texas so it’s pretty flat but my towing trips are to Colorado and Utah so I’ll probably bite the bullet and go for the 3.92.

Thanks for all the advise.

Just my 2 cents :For the extra 3,100 lbs towing capacity, for me, I'll gladly give up 1 mpg. I have the 3.92 in my Rebel, and only have about 1200 miles on it. I get a solid 18 MPG with ~90% city driving.

 

[go-ram]

If anyone is interested, just for what it might be worth, the guys over at Pickuptrucks*com have a fairly complete table at the end of their 2018/2019 half-ton shootout article, including all of the transmission gear ratios for a 3.92:1 rear-end Ram 1500. The table is way down the page.

https://news.pickuptrucks.com/2018/11/whats-the-best-half-ton-truck-for-2018.html#more

The only big difference I can see for the Ram compared to the other four trucks is the ratio in reverse (3.30:1 for the Ram, 4.04:1 to 4.87:1 for the others). Wouldn't that mean that if you were trying to back up a Ram with a heavy load in the bed, or backing up a heavy trailer, or even backing an empty truck up a slope, the Ram would strain a heck of a lot more in reverse than the other trucks?

 

[Chris]

The only big difference I can see for the Ram compared to the other four trucks is the ratio in reverse (3.30:1 for the Ram, 4.04:1 to 4.87:1 for the others). Wouldn't that mean that if you were trying to back up a Ram with a heavy load in the bed, or backing up a heavy trailer, or even backing an empty truck up a slope, the Ram would strain a heck of a lot more in reverse than the other trucks?

Technically, yes, at the trade off of higher potential reverse speed.

4Lo mitigates most of the issue when a load is present or slow speed is needed. Since you need to stop before switching back to drive anyway, switching in and out of electronic 4Lo isn’t a big deal.

 

[Ramit392]

Just my Spin on the 3.21 and the 3.92.....I owned the 3.55 in two Rams with the 5.7 hemi and the three 3.92 in the 5.7 hemi. There is very minimal difference in towing and torque between the 3.21 and 3.92 with an 8 speed tranny. There was a good difference noted from a 3.55 to 3.92 with a 6 speed tranny it seemed the 3.55 would hunt for the lower gear more when towing over the 3.92 which would hunt way less.

I would prefer the 1 mpg loss and the extra 75 bucks or so for the 3.92 to have the extra tow and pay load capacity if and when I need it. To me its like having hp if and when I need it verses when I need it and do not have it. But again that is just me,many would be very happy with a 3.21 I'm sure.

 

[TwinSac]

The 3.92 option adds roughly 3000 pounds of towing capacity. Is the only difference between the two (3.31 vs 3.92) just the ratio?

That seems like a lot of difference in weight. Brakes, bearings and axles the same?

I would think it's more important to stop while towing than it is to start. If the 3.92 can tow that much weight safely, wouldn't the 3.21 be just as safe? Might take a while to get going but can handle the weight just the same.

 

[Gondul]

Just my 2 cents :For the extra 3,100 lbs towing capacity, for me, I'll gladly give up 1 mpg. I have the 3.92 in my Rebel, and only have about 1200 miles on it. I get a solid 18 MPG with ~90% city driving.

Not getting anything near that on mine...

Just took a trip from FL to WI
75mph and cruise control, 87 octane
15 mpg was average
14 mpg was worst tank
16 mpg was best tank

Have to add up the info for the ride back..

 

[devildodge]

The 3.92 option adds roughly 3000 pounds of towing capacity. Is the only difference between the two (3.31 vs 3.92) just the ratio?

That seems like a lot of difference in weight. Brakes, bearings and axles the same?

I would think it's more important to stop while towing than it is to start. If the 3.92 can tow that much weight safely, wouldn't the 3.21 be just as safe? Might take a while to get going but can handle the weight just the same.

I believe it has to do with SAE J2807.

Look here 2nd post.

https://5thgenrams.com/community/th...et-my-needs-or-am-i-waiting-for-the-2500.437/

You are right. Nothing else is different...would guess the Ram is rated to stop even more weight.

Basically the truck is rated to stop say 15000 so the gears have nothing to do with that. And then each gear ratio allows for more or less weight to move.

 

[RenoRam]

I agree that 3.92 is better option for towing at any weight as I would rather have the capability at any time. I have a 6000lb trailer so it is needed imo. If I was looking for gas mileage, I probably wouldn't be driving a truck.

 

[Goatmann]

I get a solid 18 MPG with ~90% city driving.

Sorry, I find this very hard to believe. You must drive 45MPH down hill and never hit a stop light.

Log your mileage and tank fills on Fuelly.com.

 

[Zeronet]

The 3.21 gears put significantly (~20%) more stress and heat on the transmission. Drive shaft and pinion stress too. Could explain some of the 3000lb tow capacity difference.

 

[Gman]

Max torque for the 5.7l Hemi is at 3,950 RPM, max HP is at 5,600 RPM. The torque is available without high RPM. I don't live where everything is flat and the 3.21 handles it just fine. If you're not looking to haul at max capacity, the 3.21 is probably fine for your towing and it gives you the best opportunity to maximize your mileage when you're not.