An Engineer's Ultimate Guide To 3.21 VS 3.92 Axle Ratio

[BowDown]

A fair amount at 90, not all of it, or even most, but enough to make a difference. Again, on the trip computer. Whether or not that's close to hand calc'd, who knows.

I do understand gear ratios so I'm not going to defend 3.92s and mpg, but i will say for a round trip like that, it depends on headwinds/tailwinds, drafting semis, elevation (in the mtns it makes a massive difference if you baby it up and go fast down) and for how much of that time as a % of total. To say it's impossible is false. I would also note there was virtually zero city driving outside of getting off the highway.

My trip comp usually says 15ish when i'm mostly around town with some highway, so i'm not saying i average anything out of the ordinary.

My truck with 3.21s and lowered to aero mode is at about 12-14 mpg at 90mph.
80+ kills mpg

 

[ShortStack]

I drove back and forth to the beach about 115 miles. Put it on 75 mph and was behind cars most of the way (maybe 40 miles not behind a car) and gauge said 19.8. Actually got
the beast to switch to ECO mode for a total of about 65 miles - not consecutively though. Never did the "at the pump" check - too damn lazy
Blew my mind that it actually read 19.8 moving at 75.

 

[CogitoErgoLevo]

Sorry to burst your bubble, but that is NOT your lifetime MPG. The onboard computer has no way of tracking lifetime MPG. The trip computer MPG is a rolling average of the last 500~ miles, regardless of how many miles you have on the current trip. The ONLY way to track your MPG is to manually do it with an app like Fuelly. I know this sounds ridiculous, but if you don't believe me, check the regular MPG screen after driving a full tank of fuel through it without resetting... guarantee it will match your trip MPG screen even with 8K+ miles on the trip.

Thank you for the explanation.

 

[HSKR R/T]

Sorry to burst your bubble, but that is NOT your lifetime MPG. The onboard computer has no way of tracking lifetime MPG. The trip computer MPG is a rolling average of the last 500~ miles, regardless of how many miles you have on the current trip. The ONLY way to track your MPG is to manually do it with an app like Fuelly. I know this sounds ridiculous, but if you don't believe me, check the regular MPG screen after driving a full tank of fuel through it without resetting... guarantee it will match your trip MPG screen even with 8K+ miles on the trip.

If you never reset trip B since new then it will hold lifetime MPG. I was trying to do that, but playing with my Tazer, I accidentally had it set of trip B when I reset after a fill up and cleared it out.

 

[BowDown]

If you never reset trip B since new then it will hold lifetime MPG. I was trying to do that, but playing with my Tazer, I accidentally had it set of trip B when I reset after a fill up and cleared it out.

Trip B has a max of 9,999 miles before it resets, all you can get is a 9,999 mile average, I don't touch trip B and it reset at 9,999 miles. I assume Trip A is the same but I reset it every fillup to verify mpg

 

[BowDown]

Sorry to burst your bubble, but that is NOT your lifetime MPG. The onboard computer has no way of tracking lifetime MPG. The trip computer MPG is a rolling average of the last 500~ miles, regardless of how many miles you have on the current trip. The ONLY way to track your MPG is to manually do it with an app like Fuelly. I know this sounds ridiculous, but if you don't believe me, check the regular MPG screen after driving a full tank of fuel through it without resetting... guarantee it will match your trip MPG screen even with 8K+ miles on the trip.

I dont think thats accurate, My trip B didn't reset until 9,999 miles then at 10,000 it went to 1.

The owner's manual makes no mention of 500 mile resets, where did you read that?

Trip Push and release the up or down arrow button until the Trip menu item is highlighted in the instrument cluster display. Push and release the right or left arrow buttons to enter the submenus of Trip A and Trip B. The Trip A or Trip B information will display the following: • Distance • Average Fuel Economy • Elapsed Time Push and hold OK button to reset all information.

 

[HSKR R/T]

Trip B has a max of 9,999 miles before it resets, all you can get is a 9,999 mile average, I don't touch trip B and it reset at 9,999 miles. I assume Trip A is the same but I reset it every fillup to verify mpg

Guess I didn't make it to that mileage before I accidentally reset. Good to know.

 

[Rebelguy2020]

Trip B has a max of 9,999 miles before it resets, all you can get is a 9,999 mile average, I don't touch trip B and it reset at 9,999 miles. I assume Trip A is the same but I reset it every fillup to verify mpg

My trip B is at 13,456km, but the hours is only at just over 19 hrs, the hour meter definitely reset at some point.

 

[Redfour5]

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.

Just as a heads up, if you do a search on the differences between a 3.21 and a 3.92 your post comes up everywhere as a resource.

 

[HSKR R/T]

Just as a heads up, if you do a search on the differences between a 3.21 and a 3.92 your post comes up everywhere as a resource.

And yet it hasn't ended the debate.

 

[Mountain Whiskey]

And yet it hasn't ended the debate.

That's because some people refuse to admit they purchased the inferior gearing with 3.21!

 

[BowDown]

 

[Cliffrunner88]

View attachment 99650

She’s not wrong

 

[tidefan1967]

Most people"got" whatever gears they have because that's what was available when they bought their truck off the lot. I don't care what anyone says but most people don't special order, they just look around until they find a vehicle that meets their criteria and then they buy it. I doubt even 10% of all the buyers out there even even know what gears their truck has much less requested a specific gear when they were truck shopping to begin with.

 

[Scram1500]

And yet it hasn't ended the debate.

Opinions are like buttholes, everyone has one and they stink

 

[Redfour5]

Most people"got" whatever gears they have because that's what was available when they bought their truck off the lot. I don't care what anyone says but most people don't special order, they just look around until they find a vehicle that meets their criteria and then they buy it. I doubt even 10% of all the buyers out there even even know what gears their truck has much less requested a specific gear when they were truck shopping to begin with.

I found one that had every single thing I wanted including the tow package and off road package/LED package (as part of the built to serve edition), sprayed in bedliner and side steps/NERF were a part of my boxes checked also and at least one thing I didn't care about but it is growing on me fast (rambox/storage management system). So, the ONE AND ONLY THING it did not have was the 3.92 gearing.

I appear to be one of the few except others specifically here that cared. BUT the tow ratings were right in my range with a good thousand lbs above what my max could ever be. AND the payload was a good hundred lbs above my old 2015 so I knew I was 'in the ballpark" and then I watched the TFL truck video on a 3.21 going up the Ike gauntlet MAXED out on its load from both a payload AND a total weight. I noticed they even removed the tonneau cover to stay within payload,

SO, sleeping on it, I pulled the trigger with an amazing offer on my 2015 to buy. BUT, I still cannot figure out WHY whoever ordered this 59K unit obviously ready to tow did NOT spend another 95 bucks on that 3.92 gearing. Other than that it is an almost perfect TV for me, but looks like (See TFL video) it's gonna be fine.

 

[silver billet]

I found one that had every single thing I wanted including the tow package and off road package/LED package (as part of the built to serve edition), sprayed in bedliner and side steps/NERF were a part of my boxes checked also and at least one thing I didn't care about but it is growing on me fast (rambox/storage management system). So, the ONE AND ONLY THING it did not have was the 3.92 gearing.

I appear to be one of the few except others specifically here that cared. BUT the tow ratings were right in my range with a good thousand lbs above what my max could ever be. AND the payload was a good hundred lbs above my old 2015 so I knew I was 'in the ballpark" and then I watched the TFL truck video on a 3.21 going up the Ike gauntlet MAXED out on its load from both a payload AND a total weight. I noticed they even removed the tonneau cover to stay within payload,

SO, sleeping on it, I pulled the trigger with an amazing offer on my 2015 to buy. BUT, I still cannot figure out WHY whoever ordered this 59K unit obviously ready to tow did NOT spend another 95 bucks on that 3.92 gearing. Other than that it is an almost perfect TV for me, but looks like (See TFL video) it's gonna be fine.

Our trucks are payload limited. You could throw a 5.30 in there for all I care, you still can't tow anymore and all you're doing is wasting gas.

I factory ordered my truck, with towing expicity in mind: I got big horn, 4x4, level 2, brake controller ... and 3.21. No off road group, no heavy ram boxes, no panormaic sunroof, no etorque, nothing that would add needless weight and cut down on my payload.

The result is a relatively modestly equipped truck; it's very comfortable, and is an amazing highway cruiser. I get good gas mileage unloaded, have whatever I need for winter (4x4 + heated seats/wheel), and have 1750 pounds of payload. That payload is way above average, and means I can tow more than many guys with the 3.92, especially the more upscale trims.

So what's the point of the 3.92? Larger tires and offroading, that's about it. It's not about the initial 95 bucks, its the fact that everytime you hit 8th gear (which is where my truck lives), you're paying for a gear ratio that offers you no advantage beyond a slightly easier first and second gear pull while towing heavier loads. Just take your time with the 3.21 and its all good.

 

[SpeedyV]

Most people"got" whatever gears they have because that's what was available when they bought their truck off the lot. I don't care what anyone says but most people don't special order, they just look around until they find a vehicle that meets their criteria and then they buy it. I doubt even 10% of all the buyers out there even even know what gears their truck has much less requested a specific gear when they were truck shopping to begin with.

Ordered in May 2018.

 

[Redfour5]

Our trucks are payload limited. You could throw a 5.30 in there for all I care, you still can't tow anymore and all you're doing is wasting gas.

I factory ordered my truck, with towing expicity in mind: I got big horn, 4x4, level 2, brake controller ... and 3.21. No off road group, no heavy ram boxes, no panormaic sunroof, no etorque, nothing that would add needless weight and cut down on my payload.

The result is a relatively modestly equipped truck; it's very comfortable, and is an amazing highway cruiser. I get good gas mileage unloaded, have whatever I need for winter (4x4 + heated seats/wheel), and have 1750 pounds of payload. That payload is way above average, and means I can tow more than many guys with the 3.92, especially the more upscale trims.

So what's the point of the 3.92? Larger tires and offroading, that's about it. It's not about the initial 95 bucks, its the fact that everytime you hit 8th gear (which is where my truck lives), you're paying for a gear ratio that offers you no advantage beyond a slightly easier first and second gear pull while towing heavier loads. Just take your time with the 3.21 and its all good.

"Our trucks are payload limited. You could throw a 5.30 in there for all I care, you still can't tow anymore and all you're doing is wasting gas."

I am in total agreement. I bought specifically for towing my existing travel trailer. That is it's primary purpose other than visits to the transfer station maybe some light off roading... In the general marketing, literature and practically every dealer, they NEVER mention payload. It is always absolute tow rating that gets noted like some kind of competition when IN FACT, the payload is the critical factor for staying both legal and safe. I learned this with my Subaru and a pop up now 16/17 years ago. I actually used to put the battery on the back of the pop up to stay within the tongue weight rating on my Subaru. Then a marketing puke became their CEO and marketing started overriding the engineers who used to run the company. The difference between my 2004 and 2007 towing the same pop up showed those differences as they softened springs jerked with the wheel to wheel steering set up. I had to buy STi pink springs in the 2007 to get that one to tow right although specs were supposedly identical. A former Suby engineer told me what happened there.

I bought my 2015 to tow and now this new one. I'm good on total weight, but that payload is always a challenge but one I have always paid very close attention to. Sorry, I'm old and like a few bells and whistles. That level 2 Bighorn isn't exactly spartan. I have level 1 itself not spartan. I was quite spartan until a few years ago. Now I'm retired and what the heck, it's time to enjoy life a bit, but I will always be cognizant of not putting me and mine at risk. Ignorance is no excuse but the manufacturers and certainly the dealers (generalization) who have been known to mislead and even the supposed car mags and websites don't make it easy to be informed. The marketing wanks are often the biggest problem in the equation imho. This particular thread is likely the clearest I've ever seen on this particular issue.

 

[Whoa_Ram]

Sorry to burst your bubble, but that is NOT your lifetime MPG. The onboard computer has no way of tracking lifetime MPG. The trip computer MPG is a rolling average of the last 500~ miles, regardless of how many miles you have on the current trip. The ONLY way to track your MPG is to manually do it with an app like Fuelly. I know this sounds ridiculous, but if you don't believe me, check the regular MPG screen after driving a full tank of fuel through it without resetting... guarantee it will match your trip MPG screen even with 8K+ miles on the trip.

You are correct! It's not a lifetime MPG at all. I've noticed it and tracked it and realized it is not. I'm using the Fuelly app and track every fuel up in my truck so far.