Gear Switch 3.21 to 3.92

[2wd]

Hey, I'd like to shake this tree a little. I'm in the Coast Guard, and just got orders from the Houston area to Valdez, Alaska. I have a 2019 1500 with 3.21s. We just bought a bigger camper also! We're basically going from a lot of flat and straight to a lot of mountain twisties. I called two local dealers and they said they couldn't do it, no matter what the price was because they couldn't reflash the computer to make it work, but they both told me a couple local 4x4 shops could. My truck only has 19000 miles on it and I'd like to keep the factory warranty. To put it simply, I'd like to tow my camper and not be right at the max capacity through only Alaska/Canada mountains. Has anyone on here actually been able to get swapped out to 3.92s by a ram dealer? If so, where did you go, and what was the price?

What is the size of your trailer? Don't be afraid to operate at the max of the 3.21 for towing (8k lbs range). The 3.21 is very underrated by the manufacturer. You have a gear for gear mechanical advantage over a Toyota Tundra with 4.10's with your 3.21 thanks to the 8 speed. If you're much more than 8k you should probably be looking to a heavy duty truck.

 

[RBJ]

This was posted in February here by another member, an engineer; I thought you may find it of interest:

Jack said:
I hope this post will help to end the debate with facts and not opinions, and become THE post people refer to those who are having a hard time deciding.

You already know that 3.92 is better for towing, and 3.21 gets better fuel economy, so I will talk about what you might not know

Bottom line up front:

In layman's terms, to conceptualize the difference, imagine

1) 5 out the of 8 gears have the same final drive ratio between 3.21 and 3.92.

2) 3.21 has "an extra" overdrive gear.

3) 3.21 has 2 unique lower gears for towing.

4) 3.92 has 3 unique lower gears for towing.

5) Speed range that 3.21 is better at towing: 31-38 MPH, 48-57 MPH.

6) Speed range that 3.92 is better at towing: 0-30 MPH, 39-47MPH, 58-70 MPH.


Explanation


1) 5 out the of 8 gears have the same final drive ratio between 3.21 and 3.92:

Here's the gear ratio for the 8 speed transmission:
1) 4.71:1 2) 3.14:1 3) 2.10:1 4) 1.67:1 5) 1.29:1 6) 1.00:1 7) 0.84:1 8) 0.67:1 Reverse) 3.30:1

Final drive ratios with 3.21

1st. 15.12, 2nd. 10.10, 3rd. 6.74, 4th. 5.36, 5th. 4.14, 6th. 3.21, 7th. 2.70, 8th. 2.15, R 10.6

Final drive ratios with 3.92

1st. 18.46, 2nd. 12.31, 3rd. 8.23, 4th. 6.55, 5th. 5.06, 6th. 3.92, 7th. 3.29, 8th. 2.62, R 12.94

From the list below, we can see that gears 3-7 in 3.21 matches gears 4-8 in 3.92:

-- NO MATCH -- = 18.46 - 1st - 3.92
3.21 - 1st - 15.12 = -- NO MATCH --
-- NO MATCH -- = 12.31 - 2nd - 3.92
3.21 - 2nd - 10.1 = -- NO MATCH --
-- NO MATCH -- = 8.23 - 3rd - 3.92
3.21 - 3rd - 6.74 = 6.55 - 4th - 3.92
3.21 - 4th - 5.36 = 5.06 - 5th - 3.92
3.21 - 5th - 4.14 = 3.92 - 6th - 3.92
3.21 - 6th - 3.21 = 3.29 - 7th - 3.92
3.21 - 7th - 2.70 = 2.62 - 8th - 3.92
3.21 - 8th - 2.15 = -- NO MATCH --

2) 3.21 has "an extra" overdrive gear:

The 8th gear in 3.92 is the 7th gear in 3.21, thus effectively mean the 8th gear in the 3.21 is an extra gear to the 3.92.

Meaning, when you go test drive the 3.21 you will have to downshift to 7th to get the same acceleration at 3.92's 8th on freeways. That is why some people complain about how "sloppy" the 3.21 is, because the 3.21 has an extra overdrive gear for fuel economy. If you shift 3.21 in 7th gear, you will get the same acceleration as the 3.92 in 8th on the freeway. No, 3.21 isn't sloppy, you're just in a gear that 3.92 does not have.

3) 3.21 has 2 unique lower gears for towing:

As we know from 1), 5 gears have the same final drive ratio.
You "gain" an overdrive gear, but you "lose" one towing gear.
Here's the final drive ratio for the 2 towing gears.
1st. 15.12, 2nd. 10.10,

4) 3.92 has 3 unique lower gears for towing:

Same logic as the last
Final drive for 3 towing gears.
1st. 18.46, 2nd. 12.31, 3rd. 8.23.

5) Speed range where 3.21 is better at towing: 31-38 MPH, 48-57 MPH,
AND
6) Speed range where 3.92 is better at towing: 0-30 MPH, 39-47MPH, 58-70 MPH:

Calculated towing shift point to be 6000 rpm, if I'm off the logic is the same but the speed will vary.

For towing,
From the speed 0-30 MPH, 3.92 has higher final drive ratio over 3.21 (18.46 vs 15.12) until it has to shift to 2nd gear at 30MPH.

From the speed 31-38 MPH, 3.21 has higher final drive ratio over 3.92 (15.12 vs 12.31) until it has to shift to 2nd gear at 38MPH.

From the speed 39-47 MPH, 3.92 has higher final drive ratio over 3.21 (12.31 vs 10.10) until it has to shift to 3rd gear at 47 MPH.

From the speed 48-57 MPH, 3.21 has higher final drive ratio over 3.92 (10.10 vs 8.23) until it has to shift to 3rd gear at 57 MPH.

From the speed 58-70 MPH, 3.92 has higher final drive ratio over 3.21 (8.23 vs 6.74) until it has to shift to 4th gear at 70 MPH.

The key takeaway here is that towing heavier trailers uphill with 3.21 might never reach the desired speed within the 58-70 MPH range (typical highway towing speed) because 3.21 jumps from 10.10 to 6.74 without the 8.23 final drive ratio found in 3.92 that really help maintaining highway towing speed at max load.

Do you value the "extra" overdrive gear for fuel economy? or do you value the extra towing capability that you tell yourself you might one day need? That's up to you.

 

[IvoryHemi]

Hey, I'd like to shake this tree a little. I'm in the Coast Guard, and just got orders from the Houston area to Valdez, Alaska. I have a 2019 1500 with 3.21s. We just bought a bigger camper also! We're basically going from a lot of flat and straight to a lot of mountain twisties. I called two local dealers and they said they couldn't do it, no matter what the price was because they couldn't reflash the computer to make it work, but they both told me a couple local 4x4 shops could. My truck only has 19000 miles on it and I'd like to keep the factory warranty. To put it simply, I'd like to tow my camper and not be right at the max capacity through only Alaska/Canada mountains. Has anyone on here actually been able to get swapped out to 3.92s by a ram dealer? If so, where did you go, and what was the price?

I honestly wouldn’t spend the money on switching gears.

Because of the heavy tongue weights on a camper you are going to run out of payload long before you run out of towing capacity.

I have 3.92 and 11,300 lb tow rating. With our 6,500-7,000 lb camper and the family loaded, I’m right up against the Ram’s 7,100 lb GVWR.

Sure 3.92 will tow better than 3.21, but not significantly enough to justify spending $2,000+ on a gear swap

 

[aimlowrobin]

Have had multiple trucks with each gears. All lifted with 35s and tow with all. Not enough difference to me to influence my previous 3 truck purchases. I took whatever gears are in the truck that I liked and bought. Literally care more about the color than gears that happen to be in it.

 

[Bama2020]

Diablosport T2. Sold the truck so I have it up for sale now if you want. Got it with the extra pcm

Lil bit late but did you ever find a buyer for the pcm/diablo?

 

[Orion10182011]

If you have the 4x4 it's probably not going to be worth the cost.

 

[Topcorns336]

This was posted in February here by another member, an engineer; I thought you may find it of interest:

Jack said:
I hope this post will help to end the debate with facts and not opinions, and become THE post people refer to those who are having a hard time deciding.

You already know that 3.92 is better for towing, and 3.21 gets better fuel economy, so I will talk about what you might not know

Bottom line up front:

In layman's terms, to conceptualize the difference, imagine

1) 5 out the of 8 gears have the same final drive ratio between 3.21 and 3.92.

2) 3.21 has "an extra" overdrive gear.

3) 3.21 has 2 unique lower gears for towing.

4) 3.92 has 3 unique lower gears for towing.

5) Speed range that 3.21 is better at towing: 31-38 MPH, 48-57 MPH.

6) Speed range that 3.92 is better at towing: 0-30 MPH, 39-47MPH, 58-70 MPH.


Explanation


1) 5 out the of 8 gears have the same final drive ratio between 3.21 and 3.92:

Here's the gear ratio for the 8 speed transmission:
1) 4.71:1 2) 3.14:1 3) 2.10:1 4) 1.67:1 5) 1.29:1 6) 1.00:1 7) 0.84:1 8) 0.67:1 Reverse) 3.30:1

Final drive ratios with 3.21

1st. 15.12, 2nd. 10.10, 3rd. 6.74, 4th. 5.36, 5th. 4.14, 6th. 3.21, 7th. 2.70, 8th. 2.15, R 10.6

Final drive ratios with 3.92

1st. 18.46, 2nd. 12.31, 3rd. 8.23, 4th. 6.55, 5th. 5.06, 6th. 3.92, 7th. 3.29, 8th. 2.62, R 12.94

From the list below, we can see that gears 3-7 in 3.21 matches gears 4-8 in 3.92:

-- NO MATCH -- = 18.46 - 1st - 3.92
3.21 - 1st - 15.12 = -- NO MATCH --
-- NO MATCH -- = 12.31 - 2nd - 3.92
3.21 - 2nd - 10.1 = -- NO MATCH --
-- NO MATCH -- = 8.23 - 3rd - 3.92
3.21 - 3rd - 6.74 = 6.55 - 4th - 3.92
3.21 - 4th - 5.36 = 5.06 - 5th - 3.92
3.21 - 5th - 4.14 = 3.92 - 6th - 3.92
3.21 - 6th - 3.21 = 3.29 - 7th - 3.92
3.21 - 7th - 2.70 = 2.62 - 8th - 3.92
3.21 - 8th - 2.15 = -- NO MATCH --

2) 3.21 has "an extra" overdrive gear:

The 8th gear in 3.92 is the 7th gear in 3.21, thus effectively mean the 8th gear in the 3.21 is an extra gear to the 3.92.

Meaning, when you go test drive the 3.21 you will have to downshift to 7th to get the same acceleration at 3.92's 8th on freeways. That is why some people complain about how "sloppy" the 3.21 is, because the 3.21 has an extra overdrive gear for fuel economy. If you shift 3.21 in 7th gear, you will get the same acceleration as the 3.92 in 8th on the freeway. No, 3.21 isn't sloppy, you're just in a gear that 3.92 does not have.

3) 3.21 has 2 unique lower gears for towing:

As we know from 1), 5 gears have the same final drive ratio.
You "gain" an overdrive gear, but you "lose" one towing gear.
Here's the final drive ratio for the 2 towing gears.
1st. 15.12, 2nd. 10.10,

4) 3.92 has 3 unique lower gears for towing:

Same logic as the last
Final drive for 3 towing gears.
1st. 18.46, 2nd. 12.31, 3rd. 8.23.

5) Speed range where 3.21 is better at towing: 31-38 MPH, 48-57 MPH,
AND
6) Speed range where 3.92 is better at towing: 0-30 MPH, 39-47MPH, 58-70 MPH:

Calculated towing shift point to be 6000 rpm, if I'm off the logic is the same but the speed will vary.

For towing,
From the speed 0-30 MPH, 3.92 has higher final drive ratio over 3.21 (18.46 vs 15.12) until it has to shift to 2nd gear at 30MPH.

From the speed 31-38 MPH, 3.21 has higher final drive ratio over 3.92 (15.12 vs 12.31) until it has to shift to 2nd gear at 38MPH.

From the speed 39-47 MPH, 3.92 has higher final drive ratio over 3.21 (12.31 vs 10.10) until it has to shift to 3rd gear at 47 MPH.

From the speed 48-57 MPH, 3.21 has higher final drive ratio over 3.92 (10.10 vs 8.23) until it has to shift to 3rd gear at 57 MPH.

From the speed 58-70 MPH, 3.92 has higher final drive ratio over 3.21 (8.23 vs 6.74) until it has to shift to 4th gear at 70 MPH.

The key takeaway here is that towing heavier trailers uphill with 3.21 might never reach the desired speed within the 58-70 MPH range (typical highway towing speed) because 3.21 jumps from 10.10 to 6.74 without the 8.23 final drive ratio found in 3.92 that really help maintaining highway towing speed at max load.

Do you value the "extra" overdrive gear for fuel economy? or do you value the extra towing capability that you tell yourself you might one day need? That's up to you.

It's somewhat related, but I'd love to hear what this guy has to say about tire size increase and adjusting/regearing for shift points or tranny wear&tear. How can I pose a question to him?

Clearly I want my Speedo, ABS, and all the other tech to sync properly with the new RPMs.

Basically looking to understand if I can get away with a tuner for my '23 Laramie that I increased tire size from 285/45/22 to 285/55/22, or if I'm better off getting regeared. I'm at 3.21 gear ratio stock. I found a calculator that says I should be at 3.43 with the tire change.

I don't want an artificial change if a Tuner won't correct the root of the problem. Then again I'm just learning all of this. So maybe the tuners do the job I'm looking for.

I saw somewhere the 3.21 and 3.92 use the same gears just programmed differently?

 

[HSKR R/T]

It's somewhat related, but I'd love to hear what this guy has to say about tire size increase and adjusting/regearing for shift points or tranny wear&tear. How can I pose a question to him?

Clearly I want my Speedo, ABS, and all the other tech to sync properly with the new RPMs.

Basically looking to understand if I can get away with a tuner for my '23 Laramie that I increased tire size from 285/45/22 to 285/55/22, or if I'm better off getting regeared. I'm at 3.21 gear ratio stock. I found a calculator that says I should be at 3.43 with the tire change.

I don't want an artificial change if a Tuner won't correct the root of the problem. Then again I'm just learning all of this. So maybe the tuners do the job I'm looking for.

I saw somewhere the 3.21 and 3.92 use the same gears just programmed differently?

For starters, that guy, as a typical engineer, over thought the whole thing.

As for your tire change, you are going to a smaller tire? Just use alfaObd or one of the many other options to correct for tire size and shift points and the like will adjust accordingly

 

[Topcorns336]

For starters, that guy, as a typical engineer, over thought the whole thing.

As for your tire change, you are going to a smaller tire? Just use alfaObd or one of the many other options to correct for tire size and shift points and the like will adjust accordingly

Thanks for the reply and help! It's a larger tire.

From talking more in depth with friends who knows a lot more than I, sounds like I won't need to worry too much. Just need to find the right chip/tuner to accomplish all the goals in mind.

I'm looking to stop MDS, adjust tire size, fix shift timing, and speedometer/odometer.

Then the Tazer DT looks appealing but I'm hesitant. I've heard great things about the Pulsar and Diablo Sport, also read horror stories on the pulsar.

Stuck in a rabbit hole.

 

[Topcorns336]

Thanks for the reply and help! It's a larger tire.

From talking more in depth with friends who knows a lot more than I, sounds like I won't need to worry too much. Just need to find the right chip/tuner to accomplish all the goals in mind.

I'm looking to stop MDS, adjust tire size, fix shift timing, and speedometer/odometer.

Then the Tazer DT looks appealing but I'm hesitant. I've heard great things about the Pulsar and Diablo Sport, also read horror stories on the pulsar.

Stuck in a rabbit hole.

Oh and not to mention, from what I've seen Diablo doesn't offer a kit yet that works for '23 models. I could be wrong but I haven't found it anywhere.

I've only seen the edge pulsar kit with monitor for '23. Don't really need the monitor, I'd want it without.

 

[HSKR R/T]

Thanks for the reply and help! It's a larger tire.

From talking more in depth with friends who knows a lot more than I, sounds like I won't need to worry too much. Just need to find the right chip/tuner to accomplish all the goals in mind.

I'm looking to stop MDS, adjust tire size, fix shift timing, and speedometer/odometer.

Then the Tazer DT looks appealing but I'm hesitant. I've heard great things about the Pulsar and Diablo Sport, also read horror stories on the pulsar.

Stuck in a rabbit hole.

If you are going to a larger tire it will make your heart ratio a lower numbers not a higher number. Maybe if you had 3.92 it would make it a 3.4x.

I have the TazerDT and Pulsar. Both work great as long as you understand how to use them as they aren't compatible for steering wheel controls. Although I can't comment on 2023 compatibility

 

[Ramroo]

^^^
Thats exactly why people put larger tires on their 3.92…. trying to be 3.21.

Should have just bought a 3.21.

 

[Idahoktm]

It's somewhat related, but I'd love to hear what this guy has to say about tire size increase and adjusting/regearing for shift points or tranny wear&tear. How can I pose a question to him?

Clearly I want my Speedo, ABS, and all the other tech to sync properly with the new RPMs.

Basically looking to understand if I can get away with a tuner for my '23 Laramie that I increased tire size from 285/45/22 to 285/55/22, or if I'm better off getting regeared. I'm at 3.21 gear ratio stock. I found a calculator that says I should be at 3.43 with the tire change.

I don't want an artificial change if a Tuner won't correct the root of the problem. Then again I'm just learning all of this. So maybe the tuners do the job I'm looking for.

I saw somewhere the 3.21 and 3.92 use the same gears just programmed differently?

You're doing the calculations for gear ratio backwards. If you install 34's in place of 32's, your 3.21 gear ratio would be 3.02.

3.21 and 3.92 do not use the same gears. That doesn't make any sense.

 

[Topcorns336]

If you are going to a larger tire it will make your heart ratio a lower numbers not a higher number. Maybe if you had 3.92 it would make it a 3.4x.

I have the TazerDT and Pulsar. Both work great as long as you understand how to use them as they aren't compatible for steering wheel controls. Although I can't comment on 2023 compatibility

Running them together you can't use the steering wheel controls? Every YouTube video I watched made it seem like they would work together fine.

Tazer and pulsar both state '23 compatability. I'd love to disable the MDS with Pulsar.

Tazer seems fun but not sure if I need it, especially if pulsar takes care of the performance adjustments I'm looking for.

 

[Idahoktm]

^^^
Thats exactly why people put larger tires on their 3.92…. trying to be 3.21.

Should have just bought a 3.21.

Putting bigger tires on a 3.21 truck makes them even more useless than they already were. Look at topcorns ratio with 34's...3.02. That's good for nothing but going downhill, with a tailwind.

 

[Topcorns336]

You're doing the calculations for gear ratio backwards. If you install 34's in place of 32's, your 3.21 gear ratio would be 3.02.

3.21 and 3.92 do not use the same gears. That doesn't make any sense.

Well besides it being a learning experience for me, I blame the gear ratio calculator I used.

 

[Ramroo]

Putting bigger tires on a 3.21 truck makes them even more useless than they already were. Look at topcorns ratio with 34's...3.02. That's good for nothing but going downhill, with a tailwind.

He’s hauling A$$ downhill though.
Then you can make it back up.

 

[Ramroo]

All these folks with 3.92s putting on lifts to put on bigger tires….

 

[HSKR R/T]

Running them together you can't use the steering wheel controls? Every YouTube video I watched made it seem like they would work together fine.

Tazer and pulsar both state '23 compatability. I'd love to disable the MDS with Pulsar.

Tazer seems fun but not sure if I need it, especially if pulsar takes care of the performance adjustments I'm looking for.

You can use them together, but TazerDT no longer supports compatibility. You can only use the TazerDT with cruise control turned on. Meaning when making menu selections on the TazerDT you have to constantly turn cruise control back on to keep making selections. Sometimes, if you try to make Pulsar changes when there are TazerDT live functions running it screws with the Pulsar, and will default back to stock tune and you can't change it again until the truck power cycles.

 

[Topcorns336]

You can use them together, but TazerDT no longer supports compatibility. You can only use the TazerDT with cruise control turned on. Meaning when making menu selections on the TazerDT you have to constantly turn cruise control back on to keep making selections. Sometimes, if you try to make Pulsar changes when there are TazerDT live functions running it screws with the Pulsar, and will default back to stock tune and you can't change it again until the truck power cycles.

Thanks that's great information. Does it affect the functions of cruise control at all?