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

[theblet]

I went for the 3.92 vs 3.21 not for towing but because I plan on putting larger tires, 35's, and my friend is a whiz at calculating things like that, or at least knowing where to find it on the internet. Long story short, with 35's vs stock tires and 3.92, it will essentially bring me down to a 3.55 according t0 him.

Good plan.

 

[Mountain Whiskey]

Yes, plus the tires are heavier and the wimpy 3.21 gears will have a hard time making them roll.

 

[Dewey]

Back in

Yes, plus the tires are heavier and the wimpy 3.21 gears will have a hard time making them roll.

Back in 1999 I had Ram Sport with a 360. Talk about a super pooch. If I remember right it had 3.55’s. That thing woulda had a hard time making stock tires roll even with 4.10’s. Don’t think that’ll be a problem with the current Hemi even with 3.21’s. It’s amazing what you can do with another 150 hp. I’m amazed the huge tires guys ran back in the day with barely 200 hp.

 

[c3k]

Yes, plus the tires are heavier and the wimpy 3.21 gears will have a hard time making them roll.

Yep. Look at my sig. I put 34" on my 3.21 EcoDiesel. I've got to park at the top of a hill or I'll never get it moving.

Found that out the hard way, at the grocery store. It had a level lot. I had to have my wife push the truck to help get it moving. Then, I circled back and she had to jump into the bed (I couldn't stop or we'd have to do it again). Old girl missed on the first two jumps, but she was game and finally made it onboard before I'd gone a full mile. (I didn't want to keep circling, what with the ice cream and all.)

 

[theblet]

Yes, plus the tires are heavier and the wimpy 3.21 gears will have a hard time making them roll.

I find if I drive to work in reverse it feels like I have a 3.92. I’m doing 40mph at 4000 rpm. Ahhh the good life…….

 

[Mountain Whiskey]

I find if I drive to work I’m reverse it feels like I have a 3.92. I’m doing 40mph at 4000 rpm. Ahhh the good life…….

That's torque baby!

 

[Mountain Whiskey]

Back in

Back in 1999 I had Ram Sport with a 360. Talk about a super pooch. If I remember right it had 3.55’s. That thing woulda had a hard time making stock tires roll even with 4.10’s. Don’t think that’ll be a problem with the current Hemi even with 3.21’s. It’s amazing what you can do with another 150 hp. I’m amazed the huge tires guys ran back in the day with barely 200 hp.

I hear ya. I had an old ex military 1977 Dodge once. Put a 4 inch lift and 33s on it. The thing had Dana 60 front and rear with a 318ci motor. It was made to not have enough power to snap an axle no matter how dumb a grunt was driving it.

I have no idea what the gearing was with the 3 speed transmission but it would go 0-60 in 5.3.
Well, minutes, not seconds.....

 

[GratefulDenglish]

Skipping around the tread and have a quick maybe dumb questions...I am changing out the rear differential fluid and have the 3.92 gear set. I know it calls for 75w-140 and many have said with infrequent towing that 75w-110 would suffice. I am sure either would be fine, but figured the gallery would like to chime in. BIGGER QUESTION - I have an E-Locker and in the past on my old 5th Gen with 3.21 gears it took LS Additive. Do I need to add the Mopar LS additive to the 3.92 E-Locker? Can't seem to find a straight answer and window sticker does not have anything to help.

 

[c3k]

Skipping around the tread and have a quick maybe dumb questions...I am changing out the rear differential fluid and have the 3.92 gear set. I know it calls for 75w-140 and many have said with infrequent towing that 75w-110 would suffice. I am sure either would be fine, but figured the gallery would like to chime in. BIGGER QUESTION - I have an E-Locker and in the past on my old 5th Gen with 3.21 gears it took LS Additive. Do I need to add the Mopar LS additive to the 3.92 E-Locker? Can't seem to find a straight answer and window sticker does not have anything to help.

Someone smarter than me will reply soon, but here's my take: a Limited Slip differential needs Limited Slip additive, so that the clutch packs (the part that limits the slip) don't stick. If they stick, your rear end chatters.
If you have an E-locker...it doesn't have a clutch pack that needs Limited Slip additive. Nor will the LS additive harm anything. So, you're good to go if you use it.

 

[Mountain Whiskey]

Someone smarter than me will reply soon, but here's my take: a Limited Slip differential needs Limited Slip additive, so that the clutch packs (the part that limits the slip) don't stick. If they stick, your rear end chatters.
If you have an E-locker...it doesn't have a clutch pack that needs Limited Slip additive. Nor will the LS additive harm anything. So, you're good to go if you use it.

Yup.

 

[BowDown]

Skipping around the tread and have a quick maybe dumb questions...I am changing out the rear differential fluid and have the 3.92 gear set. I know it calls for 75w-140 and many have said with infrequent towing that 75w-110 would suffice. I am sure either would be fine, but figured the gallery would like to chime in. BIGGER QUESTION - I have an E-Locker and in the past on my old 5th Gen with 3.21 gears it took LS Additive. Do I need to add the Mopar LS additive to the 3.92 E-Locker? Can't seem to find a straight answer and window sticker does not have anything to help.

If you're replacing the gear oil with synthetic you don't as the additive is already there

 

[m.hamner]

Got my truck in for some factory items and noticed their badlander series are on 37’s with…. 3.21’s also, so are their black widow’s and rocky ridges, though those are on 33’s or 35’s. Still, interesting that they’re kitted out like that.

 

[djevox]

Got my truck in for some factory items and noticed their badlander series are on 37’s with…. 3.21’s also, so are their black widow’s and rocky ridges, though those are on 33’s or 35’s. Still, interesting that they’re kitted out like that.

View attachment 132033

I’m surprised that truck moves at all with those wimpy gears. On a similar note, I almost got the winch out for this situation out of worry for having 3.21 gears. That 4.25” grass is killer on those gears:

 

[Ramjack]

I’m surprised that truck moves at all with those wimpy gears. On a similar note, I almost got the winch out for this situation out of worry for having 3.21 gears. That 4.25” grass is killer on those gears:

View attachment 132064

LOL . . . Just pretend you're pumping a bicycle up a hill.

 

[BowDown]

Drove back from San Antonio to Dallas yesterday @80 mph. Average speed was 72 mph, traffic in Austin and Waco



Man, I wish I didn't get those wimpy 3.21 gears....

 

[SnowBlaZR2]

Lol at trying to dunk about getting 22 mpg in an empty 2WD "truck."

 

[BowDown]

Lol at trying to dunk about getting 22 mpg in an empty 2WD "truck."

Umm

About that; trying to dunk about getting 36 mpg in an empty 4wd truck will driving 49 mph

BTW, I had 4 adults and their luggage the truck

 

[SnowBlaZR2]

Umm




About that; trying to dunk about getting 36 mpg will driving 49 mph

First, 36.8 mpg is the old record. It's up to 37.9 mpg now.

Second, I didn't have to get a 2WD truck with 3.21s and pretend it weighs 5200 lbs to hit that.

 

[ferraiolo1]

Still won’t show the real mpg screen with a higher milage though.


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[SnowBlaZR2]

Best I got. I have a truck, not a minivan.



25 city/38 highway. I'll take it, and don't even have to handicap the truck to get it.