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

[Willwork4truck]

Presuming thats correct then yes, it could also mean wheel slip up loose or wet surfaces.

I had a 3.21 and could make a rt angle turn uphill from a stop and not spin the inside rear. Same kind of turn yesterday with the new 3.92 and she broke loose a fair bit. So that un-scientific experiment suggests appreciably more torque from a stop. 3.21 was non et, 3.92 has et.

All that to say backing up a trailer could in fact be harder, especially on slick surfaces. Just MHO based on backing up travel trailers years ago with a lower hp 4.10 geared open diff pickup.

 

[theblet]

I searched but couldn't find an answer - with the 3.92, the final drive ratio for first and reverse is higher, so my assumption is that when maneuvering a trailer in reverse, the 3.9 geared vehicle would be be slower at idle speed, as well as have more torque. This would be helpful if backing up a trailer on an incline correct?

Different gearing doesn’t “have more Tq”. All of the hemis have the same Hp/Tq values. A taller gear applies the Tq differently, and the engine will be in a higher rpm range in the same gear than a 3.21 will be.

 

[Rick3478]

Different gearing doesn’t “have more Tq”. All of the hemis have the same Hp/Tq values. A taller gear applies the Tq differently, and the engine will be in a higher rpm range in the same gear than a 3.21 will be.

Incorrect. Engine torque is multiplied by axle ratio, so yes taller gears are an advantage for backing uphill, pulling boats out of the water, etc.

I was wondering if park assist might be relevant to this thread. I've heard of trucks refusing to back up due to thinking the trailer is a wall that is too close, or tailgate open thinking the ground is a wall.

 

[CalvinC]

Theoretically you are right, would make backing up a load easier with more torque at the ground.

Then I recall regularly backing a 6k lb boat up my super steep & windy 1/8th mile driveway with a 98 F150 with a 4.6L V8 and 3.55s, and realize anything modern will be just fine in the real world.

What would actually be a game changer is a 2WD Lo, or even better a 4AutoLo, mode. Even more torque to the ground, better throttle modulation, and no binding.

Early 2000s Toyotas had this and was fantastic.

 

[Rick3478]

What would actually be a game changer is a 2WD Lo, or even better a 4AutoLo, mode. Even more torque to the ground, better throttle modulation, and no binding.

Early 2000s Toyotas had this and was fantastic.

I think BD Diesel makes a 2-low wiring and relay kit. That's from memory, hope I got it right.

 

[silver billet]

I searched but couldn't find an answer - with the 3.92, the final drive ratio for first and reverse is higher, so my assumption is that when maneuvering a trailer in reverse, the 3.9 geared vehicle would be be slower at idle speed, as well as have more torque. This would be helpful if backing up a trailer on an incline correct?

Two different things going on here: 1) power, 2) traction.

The hemi has more than enough power to move it's rated weight in any gear, including first/reverse. It's not even something to worry about, the hemi will push and pull whatever you want.

Traction: this is a separate problem, you may find issues on slippery boat ramps or on a grassy/sandy campsite, this is why 4x4 and/or lockers (limited slip) are your friend. I've used 4x4 auto often while getting in/out campsites. Never needed 4x4 low but that's always the next step if auto isn't doing it for you.

 

[Willwork4truck]

Exactly.
Even my old 77' GMC 1 ton single 4x (really a 2x, 1 up front, 1 in back power) and a 4.10 had enough power but traction was the issue. Going backwards up a hill with an empty bed pushing a dead weight 6000# travel trailer required a good grippy set of tires and no loose crap or wetness on the surface. Didn't work too well in summer on grass or winter on snow, that I recall...

 

[Mountain Whiskey]

I searched but couldn't find an answer - with the 3.92, the final drive ratio for first and reverse is higher, so my assumption is that when maneuvering a trailer in reverse, the 3.9 geared vehicle would be be slower at idle speed, as well as have more torque. This would be helpful if backing up a trailer on an incline correct?

The easy answer is yes.

Hemi power, blah blah blah, the stock truck is detuned so the average idiot with a student driver bumper sticker won't get hurt driving it. The transmission is the same across the board. The torque and power that matters is what is measured at the wheel. Yes this is affected by the gear ratio. The 3.92 is dominant here.

As for speed when maneuvering your boat trailer around, if you have 3.21s don't worry, you won't have enough power to move it unless it is a little girl's pedal boat and the ramp is not too steep.

If you have a man's boat pull it around with the 3.92 gears. Sure if you are an idiot stomping on the pedal while dragging weight on a wet concrete ramp, you can spin the tires. At least it CAN spin though. This is something the 3.21 "guys" are not familiar with.

So if you want a truck to do truck things, 3.92 is your choice.

If you want something to get groceries with, take a few bags of leaves to the dump in the fall, and keep your Ken doll riding shotgun on the dash, get 3.21 gears. Hey at least then you have something you can put a unicorn sticker on and give to your daughter for her sweet 16.

 

[6of36]

The easy answer is yes.

Hemi power, blah blah blah, the stock truck is detuned so the average idiot with a student driver bumper sticker won't get hurt driving it. The transmission is the same across the board. The torque and power that matters is what is measured at the wheel. Yes this is affected by the gear ratio. The 3.92 is dominant here.

As for speed when maneuvering your boat trailer around, if you have 3.21s don't worry, you won't have enough power to move it unless it is a little girl's pedal boat and the ramp is not too steep.

If you have a man's boat pull it around with the 3.92 gears. Sure if you are an idiot stomping on the pedal while dragging weight on a wet concrete ramp, you can spin the tires. At least it CAN spin though. This is something the 3.21 "guys" are not familiar with.

So if you want a truck to do truck things, 3.92 is your choice.

If you want something to get groceries with, take a few bags of leaves to the dump in the fall, and keep your Ken doll riding shotgun on the dash, get 3.21 gears. Hey at least then you have something you can put a unicorn sticker on and give to your daughter for her sweet 16.

My 4th Ram had a 6, and towed my almost 6,000 lb boat just fine, except on steep inclines. My Hemi trucks have all done great with 3.21s. I never even put in 4wd at the boat ramp, although some boat ramps are more slippery, and would need 4wd. With a large heavy trailer I would recommend 3.92, but up to 6,000 lbs, 3.21 is sufficient.

 

[theblet]

My 4th Ram had a 6, and towed my almost 6,000 lb boat just fine, except on steep inclines. My Hemi trucks have all done great with 3.21s. I never even put in 4wd at the boat ramp, although some boat ramps are more slippery, and would need 4wd. With a large heavy trailer I would recommend 3.92, but up to 6,000 lbs, 3.21 is sufficient.

If you have insufficient “manhood” I’d recommend 3.92s as well

 

[Ramfancy]

I can only imagine 2 reasons why I would choose 3.92 over 3.21.

If I towed in very steep hills a lot. It would have better acceleration taking off on steep grades. I am sure it feels more capable in that setting.

If I wanted to get taller or much heavier tires. My days of tricking out a trail beast are over. Maybe in my younger days.

I pulled a couple campers this fall to test out my Laramie with the 3.21. 1730 payload maxes out pretty fast. A 7000 and change 27 footer towed beautifully. Had 0 issues. Probable maxed out payload and I knew it was there all the time, but was a great experience. Medium hills did not bother the hemi.

65% of my miles are on the highway. About 25% are in town, and the rest are towing a camper. The extra mileage adds up to be pretty respectable in my scenario.

This hemi rocks compared to my old 4.7.

 

[Willwork4truck]

I can only imagine 2 reasons why I would choose 3.92 over 3.21.

If I towed in very steep hills a lot. It would have better acceleration taking off on steep grades. I am sure it feels more capable in that setting.

If I wanted to get taller or much heavier tires. My days of tricking out a trail beast are over. Maybe in my younger days.

I pulled a couple campers this fall to test out my Laramie with the 3.22. 1730 payload maxes out pretty fast. A 7000 and change 27 footer towed beautifully. Had 0 issues. Probable maxed out payload and I knew it was there all the time, but was a great experience. Medium hills did not bother the hemi.

65% of my miles are on the highway. About 25% are in town, and the rest are towing a camper. The extra mileage adds up to be pretty respectable in my scenario.

This hemi rocks compared to my old 4.7.

My heavy trailering days are past as well, so why did I end up with a 3.92 when this truck just goes to Home Depot or Lowes for dirt, concrete blocks etc… well it is what the dealer had at the time, there were 2, just 2 end of year 2023’s left that were decked out Limiteds. Both had 3.92, which although it is costing me a 3+ mpg hit (my 2019 same truck with 3.21’s, doing the same “work”, consistently returned the better highway 21-22 vs this ones 18 per the lieometer.)

I justified the 3.92’s for resale as I usually keep a vehicle less than 4 years despite swearing that “this one is a keeper”. 3 new vehicles since 2019 adds up to a lot of expensive changes. The 3.92 will sell quicker, not for any more money but likely a peep will choose this 3.92 over a similar 3.21. Why you ask?

Towing prowness is the reason, while next to no one remembers that the wimpy 1370 lb payload is what gets you first. Most everyone is all about the “towing wars” number, which is kinda’ dumb. A greenhorn trying to tow a 32+ foot long multi-slide 10K + GVW travel trailer would quickly find out he is significantly under-trucked.

So to say that the 3.21 isn’t good for under 6.5K towing loads isn’t correct, yet that 12-13% tongue weight before anything else is put in the truck (other than driver and fuel) is going to be your reasonable limit.
”Frontal sail area, what’s that?”

Note I say “reasonable” as there is no end to folks towing too big with 1500’s on the highways and going 75 mph as well. Just accidents waiting to happen IMHO.

I will try to link one of the several “too big travel trailer, tail wagging the dog ending up overturned on the road” YT videos. Here‘s an example, look up YT:

RV Crashes That Could Of Been Avoided | RV Fails |RV Accidents | RV Wreck|RV Crash​

The first one shows a too long trailer, or conversely a too short wheelbase tow vehicle. Probably overloaded as well.
“Flame on…”

 

[Ramfancy]

My heavy trailering days are past as well, so why did I end up with a 3.92 when this truck just goes to Home Depot or Lowes for dirt, concrete blocks etc… well it is what the dealer had at the time, there were 2, just 2 end of year 2023’s left that were decked out Limiteds. Both had 3.92, which although it is costing me a 3+ mpg hit (my 2019 same truck with 3.21’s, doing the same “work”, consistently returned the better highway 21-22 vs this ones 18 per the lieometer.)

I justified the 3.92’s for resale as I usually keep a vehicle less than 4 years despite swearing that “this one is a keeper”. 3 new vehicles since 2019 adds up to a lot of expensive changes. The 3.92 will sell quicker, not for any more money but likely a peep will choose this 3.92 over a similar 3.21. Why you ask?

Towing prowness is the reason, while next to no one remembers that the wimpy 1370 lb payload is what gets you first. Most everyone is all about the “towing wars” number, which is kinda’ dumb. A greenhorn trying to tow a 32+ foot long multi-slide 10K + GVW travel trailer would quickly find out he is significantly under-trucked.

So to say that the 3.21 isn’t good for under 6.5K towing loads isn’t correct, yet that 12-13% tongue weight before anything else is put in the truck (other than driver and fuel) is going to be your reasonable limit.
”Frontal sail area, what’s that?”

Note I say “reasonable” as there is no end to folks towing too big with 1500’s on the highways and going 75 mph as well. Just accidents waiting to happen IMHO.

I will try to link one of the several “too big travel trailer, tail wagging the dog ending up overturned on the road” YT videos. Here‘s an example, look up YT:

RV Crashes That Could Of Been Avoided | RV Fails |RV Accidents | RV Wreck|RV Crash​

The first one shows a too long trailer, or conversely a too short wheelbase tow vehicle. Probably overloaded as well.
“Flame on…”

I too bought the only Ram the dealer had that included most options I wanted. If it would have had the 3.92, I still would have bought it. Lose a little mileage, but gain a little giddy up!

 

[Mountain Whiskey]

If you have insufficient “manhood” I’d recommend 3.92s as well

I see the 3.21 focus on manhood.... Not that there's anything wrong with that!

I can only imagine 2 reasons why I would choose 3.92 over 3.21.

1. So I can drive a truck.
2. So the girls in the Jeeps don't laugh when my truck can't keep up with their Wrangler.

 

[Ramfancy]

I see the 3.21 focus on manhood.... Not that there's anything wrong with that!

1. So I can drive a truck.
2. So the girls in the Jeeps don't laugh when my truck can't keep up with their Wrangler.

Pretty good, but I can think of a lot of better things to do with pretty girls than race them in my truck!

 

[ferraiolo1]

It’s always the lifted truck and low gear ratio guys trying to compensate.


Sent from my iPhone using Tapatalk

 

[6of36]

If you have insufficient “manhood” I’d recommend 3.92s as well

True, guys with insufficient manhood need 3.92s. Me, I'm retired. No need to prove my manhood.

 

[Ramfancy]

Pretty good thread, boys!

 

[Rick3478]

Do we need to re-title this thread to "A Therapist's Ultimate Guide..."?

 

[HSKR R/T]

Do we need to re-title this thread to "A Therapist's Ultimate Guide..."?

Probably more retitle it to battle of the sexes. Which one is which is up to you