3.21 vs 3.92 Gear Ratio...will not be towing much.

[Gooseit]

I just changed from 3:21to 392 gears and this is what I have observed. 1. At 70 mph it turns 500 rpm more. 2. I have lost gas mileage. 3. I have gained A LOT of low end grunt, big difference. 4. If I were going to do a lot of interstate traveling I would not go with the 3:92, but for around town driving like I do I love it My truck is a two-wheel drive lowered vehicle.

 

[runamuck]

I didnt think there would be more than a cpl, hundred rpms difference..anyhow, I have had a couple earlier ram trucks and several chevy/gmc 1500's and this truck handles the best and is more fun to drive than any of the others.

 

[Beltsand]

I can't believe I read this whole thread. Talk about going down the rabbit hole. Here are my takeaways from this:

- Higher reduction is better for low end torque
- Lower reduction is better for high speed gas mileage
- the ZF 8 speed broadens the range for both standard factory axles over the previous gen RAM 1500 trucks
- don't ignore the effect of tire size on the overall drive ratio - larger tire diameter lowers the effective ratio
- people still get confused between GCWR, GVWR, curb weight, payload (almost typed playload, still seems appropriate), axle rating, and tow capacity
- the limit on my setup is most likely going to be payload, yours may not be
- these trucks are awesome
- people on this forum know a lot about these trucks

 

[VeDubb]

I have a lowered Ram 1500 with the 8 speed and 3.92 gear. If empty I can get 22 easily on the highway. Of course, that's if I keep it under 78 mph. Once over 78 mph the mpg goes down significantly! One other thing to consider... If you lower it you'll lose some of the smooth ride especially with 22's.

 

[Lucy Girl]

321. My third Ram with 321. Only way to go.

 

[Mountain Whiskey]

What have you guys experienced when installing 35 inch tires?

I am coming from Jeeps. My old jeep had the milage drop like a rock when I put 33s on it and did not regear. My 2020 has 4:10s in the pumpkins with the 8 speed. Jumping from stock to 35s suffered a little milage but would not see 8th unless I was on a downhill grade with a tailwind pushing me.

Would 3.92 and 35s in 8th be near to stock tires and 3.21?

There are some gear math wizards on here that I am sure can figure that out!

 

[Sloverado]

What have you guys experienced when installing 35 inch tires?

I am coming from Jeeps. My old jeep had the milage drop like a rock when I put 33s on it and did not regear. My 2020 has 4:10s in the pumpkins with the 8 speed. Jumping from stock to 35s suffered a little milage but would not see 8th unless I was on a downhill grade with a tailwind pushing me.

Would 3.92 and 35s in 8th be near to stock tires and 3.21?

There are some gear math wizards on here that I am sure can figure that out!

You would be around around a 3.52 going from say a stock size tire (275/55/20) to a 35” (295/65/20). There is about 10% difference in final drive ratio.

 

[Lucy Girl]

Hi everyone,

I am planning on buying a new 2021 RAM 1500 and call me crazy but I would like to achieve the best mileage possible with a V8... (really not sure about the diesel and noise, and $$$)
#1 Priority is the most quiet best riding 4x4, without paying a fortune and able to achieve the best mileage possible. Priority #2 - I won't be towing much maybe a small 2 person fishing boat short distances or a small trailer to haul stuff...under 100 miles.
Here is what I am looking at:
1500 Laramie (need me some cooled seats), Sport, V8, Laramie 2 package, Multi Function tail gate, anti spin diff, 33 gallon fuel tank, 22 inch tires, tow package.

What do I lose by not going with the 3.92 ? ARE there any other options I should consider?

Thank you!

3.21 and 8 speed transmission. Unreal. My 6 cylinder HEMI loves it.

 

[corneileous]

What have you guys experienced when installing 35 inch tires?

I am coming from Jeeps. My old jeep had the milage drop like a rock when I put 33s on it and did not regear. My 2020 has 4:10s in the pumpkins with the 8 speed. Jumping from stock to 35s suffered a little milage but would not see 8th unless I was on a downhill grade with a tailwind pushing me.

Would 3.92 and 35s in 8th be near to stock tires and 3.21?

There are some gear math wizards on here that I am sure can figure that out!

Sloverado was pretty close if you had a 275/55-20 and went up to a 295/65-20. Using tiresize.com’s gear calculator, if 3.92 is what your gear ratio is then your new ratio after the new rubber would be 3.56 and you would need a 4.31 to bring it back down to 3.92.

But whatever gear you’re in with your stock tires, for every one revolution that your tires make, your drive line will have turned 3.92 times.


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[HEMIMANN]

Sloverado was pretty close if you had a 275/55-20 and went up to a 295/65-20. Using tiresize.com’s gear calculator, if 3.92 is what your gear ratio is then your new ratio after the new rubber would be 3.56 and you would need a 4.31 to bring it back down to 3.92.

But whatever gear you’re in with your stock tires, for every one revolution that your tires make, your drive line will have turned 3.92 times.


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What a useful chart that is! Perfect summation of 3 variables in one easy graph.

 

[corneileous]

What a useful chart that is! Perfect summation of 3 variables in one easy graph.

Yep. That’s why like when people buy those trucks with 3.21 gears and they decide to put 35’s on, their new gear ratio is way up there to around a 2.92 gear ratio if the stock tires are 275/55-20 and you went up to a 295/65-20 which isn’t quite as detrimental as it seems because even though yes, 35’s on a 3.21 geared truck is worse than 35’s on a 3.92 geared truck but if you felt it a good idea to do a gear swap- which you should, to make your truck and your drivetrain a lot happier, you could even go further than that and put in a set of gears that’ll bring your ratio up to a 3.92 which in my opinion is much better with larger and much more heavier tires since it’s like impossible to find a non-10 or 8-ply 35.

On that old 98 Ram 1500 I had, it came stock with a 245/75-16 tire and I believe a 3.73 gear ratio but when I bought it, the previous owner had put 33 inch 285/75-16 BFG all terrains that were 8-ply on it and, with that little 5.2L 318 and 5-speed, it was quite underpowered for the majority of the time I owned it and I just assumed it was because of what I thought was too small of a motor but when I dropped down to a 265/75-16 a few years later- I got rid of the BFG’s not long after buying it because they were well worn and I went though a set of much smoother-riding Yokohama Geolanders in the same size, the smaller 265’s gave quite a bit of power and performance back but if I would’ve had the money back then, I would’ve much rather preferred to do the gear swap because I sure loved how that truck looked with the 33’s. It’s like it was meant for that size tire and surprisingly the only tire rub I had was when at full turn in either direction, the inside shoulders of the front tires would rub just a little bit on the upper suspension arms that came down from the frame to the back of the front axle and that was even on really uneven terrain.


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[mmcbeat]

I’m retired and no longer drive a huge amount of miles each year. I purchased a 2021 Ram Lone Star and went with the 3.92 rear end. With my limited experience, this truck is fun to drive. City driving, hop on the entrance ramp and go. Again, I don’t drive enough to be overly concerned about mpg.

 

[Beltsand]

What have you guys experienced when installing 35 inch tires?

I am coming from Jeeps. My old jeep had the milage drop like a rock when I put 33s on it and did not regear. My 2020 has 4:10s in the pumpkins with the 8 speed. Jumping from stock to 35s suffered a little milage but would not see 8th unless I was on a downhill grade with a tailwind pushing me.

Would 3.92 and 35s in 8th be near to stock tires and 3.21?

There are some gear math wizards on here that I am sure can figure that out!

I doubt you are still looking for an answer, but I was curious on how they really stacked up. A little spreadsheet work, and I got this out. These MPH vs Engine Speed. I found these ratios for the ZF 8 speed and BW transfer case:


Gear Ratio
1 5
2 3.2
3 2.1429
4 1.72
5 1.3139
6 1
7 0.8221
8 0.64
R -3.456

transfer case 2.64
My factory tires have a 31.9" diameter, so that is what I used.



Then I changed just the 3.92 rear end to 35" tires and left the 3.21 with the 31.9.

 

[RamDutyl]

Hi everyone,

I am planning on buying a new 2021 RAM 1500 and call me crazy but I would like to achieve the best mileage possible with a V8... (really not sure about the diesel and noise, and $$$)
#1 Priority is the most quiet best riding 4x4, without paying a fortune and able to achieve the best mileage possible. Priority #2 - I won't be towing much maybe a small 2 person fishing boat short distances or a small trailer to haul stuff...under 100 miles.
Here is what I am looking at:
1500 Laramie (need me some cooled seats), Sport, V8, Laramie 2 package, Multi Function tail gate, anti spin diff, 33 gallon fuel tank, 22 inch tires, tow package.

What do I lose by not going with the 3.92 ? ARE there any other options I should consider?

Thank you!

Awesome pick! How much gas mileage will the 3.21 save you? If you don't have an exact number, you'll wake up one day wondering. You hope you won't tow much, but when you do, will that 3.21 seem limiting and lurchy? Test drive both maybe. Honestly, if you avoid jack rabbit starts, gas mileage ain't bad with a V8. Like the old 440ci V8's, stay off the secondaries and the ample low end power will get you going on minimal gas consumed.