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

[Mountain Whiskey]

To the OP - Thanks for the data and explanation.

It is great to deal in facts but too much work and not as much fun as spewing baseless opinions.

25 pages of comments and counting - the 3.21 vs. 3.92 debate is a passionate one. I have owned both. Like them both for different reasons.

Looking at your signature block, it looks like, you settled for the better gear now. Good choice!

 

[Cgs1967]

I'm lifting mine and putting 35's on it. I also tow my Ranger bass boat so I'm very happy I chose the 3:92.

 

[Cliffrunner88]

My truck is probably going to be heavier than most in this post so while I won’t be towing that often, having the 3.92 would help move my truck’s weight better than the 3.21, same as if I had a lightweight with a trailer, right?

 

[Cliffrunner88]

Also, how do y’all calculate the final drive ratios of each gear with a different tire size?

 

[Mountain Whiskey]

Also, how do y’all calculate the final drive ratios of each gear with a different tire size?

Count back a dozen or two pages and someone posted a chart.

 

[bwsRam19]

Just get the 3.92, same if you buy a challenger or charger get the 392

 

[oldsouth]

What about how they compare on acceleration. And what about the middle ratio. What is it.... 3.55.... but I just looked and its not listed on their order page now. It was when I ordered my truck.

 

[Scram1500]

What about how they compare on acceleration. And what about the middle ratio. What is it.... 3.55.... but I just looked and its not listed on their order page now. It was when I ordered my truck.

3.55 is only available for the 3.6L gas V6, and the TRX....

 

[Cliffrunner88]

So you only save MPG on the 3.21 if you’re going above ~55mph right? Otherwise you’re just in a different gear on the 3.92. But the 3.92 will have better acceleration off the line.

 

[c3k]

FWIW...
See sig.
Driving at ~75mph on the ORG stock tires/wheels, my ecodiesel in 8th gear, 3.21 gears, was showing ~1650-1700 rpm. I'm sure that number (or something close to it) is on one of the charts upstream. If I had 3.92, then I'd expect it would've been about 2,000 rpm at that speed.

 

[theblet]

So you only save MPG on the 3.21 if you’re going above ~55mph right? Otherwise you’re just in a different gear on the 3.92. But the 3.92 will have better acceleration off the line.

The 3.21 should have a lower rpm at all speeds, assuming the same transmission gears. At ~55 I’m making 22 to 25 without mds on a flat road. 30+ with mds. What are you guys seeing with 3.92s?

 

[Cliffrunner88]

The 3.21 should have a lower rpm at all speeds, assuming the same transmission gears. At ~55 I’m making 22 to 25 without mds on a flat road. 30+ with mds. What are you guys seeing with 3.92s?

I don’t think I’ve seen anyone else post 30+ mpg with regular gas. Are you 90%+ highway?

 

[theblet]

87 octane. I’m about 50/50 highway and city. 30 isn’t my average. It’s just what I see at 55 mph with the cruise set and mds kicked in.

 

[parnine]

87 octane. I’m about 50/50 highway and city. 30 isn’t my average. It’s just what I see at 55 mph with the cruise set and mds kicked in.

In honor of David Letterman ..... and for some lighthearted fun.....

If you are getting 30+ mpg on the highway you .....
10 - have proven time travel and have a 2030 model - everone else is #$*@ out of luck
9 - are confused between mpg and kpl
8 - saw '99 mpg', thought that was not right, it dropped to the 30s, so that must be it
7 - really getting 80, confusing the 3 and 8 cause cause you've 'maybe had a drink or two'
6 - Cluster is broken and no matter speed it shows 30+ mpg
5 - in addition to the mds kicking in, the ecstasy has also kicked in
4 - are Democrat, i.e. socialist, and heard everyone is getting it, so you must also
3 - are a Trumper, and after paying $50K plus, with high price due to antifa and the radical left, you have created your own reality to save on gas
2 - are actually being towed
.
.
.
.
1 - got a large guy sitting on the tail gate blowing wind out his *** .......

Vote for your favorite, or add one better

 

[oldsouth]

74 indicated 75 actual

 

[Buz]

View attachment 93283
74 indicated 75 actual

You haven't filled the spot above the speed reading on your instrument cluster.
The menu lets you pick from a few things that can go there.

 

[brian42]

70 mph on the freeway is about 1550 RPM for me with my 3.21.

On the flats during my commute in the morning (freeway with no traffic) and the cruise control set at 70 mph (which is 69 mph actual) my "Current MPG" is 22-23 mpg without MDS (no ECO) and 26-27 with MDS (ECO light).

 

[oldsouth]

You haven't filled the spot above the speed reading on your instrument cluster.
The menu lets you pick from a few things that can go there.

Thanks, I'll check it out.

 

[oldsouth]

What is this MDS yall are talking about?

 

[Buz]

Thanks, I'll check it out.

I have my clock there. You can move your clock there and then pick from a bunch of things where your clock is now.