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

[IvoryHemi]

3.92 simply gives you 22% higher rpm = more hp/torque in any given gear

 

[theblet]

3.92 simply gives you 22% higher rpm = more hp/torque in any given gear

Gears don't increase HP or TQ. They change the curve. So you will reach peak at a different RPM than with 3.21s.

 

[IvoryHemi]

Gears don't increase HP or TQ. They change the curve. So you will reach peak at a different RPM than with 3.21s.

Correct, thus rpm’s are 22% higher

 

[Buz]

And when RPM's are 22% higher, it will cause less lugging/strain on the engine, all else being equal.

 

[IvoryHemi]

And when RPM's are 22% higher, it will cause less lugging/strain on the engine, all else being equal.

exactly. Less wear/tear on the trans too

 

[lkjk]

Correct, thus rpm’s are 22% higher

I don't think that 22% is correct. 3.92 is a 22% higher than 3.21, but i don't think it's a 1 for 1 for RPMs. not saying don't get 3.92s, i have them.

 

[silver billet]

Nope; first gear will be easier take off, and yes rpms are 22% higher, but that's assuming the trucks will be using the same gear at the same speed.

They won't.

When you're truck is towing in 7th, my truck is towing in 6th at the same speed; thus we have the same rpms, and same power.

 

[silver billet]

The "wear and tear" is laughable guys; you don't want to admit to wear and tear when your truck is revving 500 rpms higher on the highway unloaded in 8th, which it will probably do for many thousands of miles more than my truck spends in first while towing, so we can also ignore wear and tear in first gear (which is the only significant difference).

My truck is rated to pull 8000 pounds. So is yours, and you won't be pulling > 8000 without going over payload. So since both our trucks can pull 8000, and are rated to do so using the J2807 standard, lets not trot out fake data to support our bias; my truck isn't going to implode by pulling my rated load. If it means it takes 2 to 3 seconds longer to get up to speed because I need to hold first gear a little longer than you (assuming we're both WOT too).... OHH MY STARS ALIVE I'M GONNA TRADE IN MY TRUCK!!!!

 

[silver billet]

There is so much drama and complete misinformation in this thread. I'm officially exiting. The funniest thing is probably none of you guys are pulling close to 8000 pounds but hey, if you feel better with the 3.92 then I hate to take your popsicle away.

You may be happy to know that I've got a new truck on order. It's a 1 ton cummins because I'm pulling 7000 pounds and I'm afraid my current a$$ end is gonna disintegrate 10 years from now.

 

[IvoryHemi]

The funniest thing is probably none of you guys are pulling close to 8000 pounds

7,980 lbs to be exact lol

 

[theblet]

There is so much drama and complete misinformation in this thread. I'm officially exiting. The funniest thing is probably none of you guys are pulling close to 8000 pounds but hey, if you feel better with the 3.92 then I hate to take your popsicle away.

You may be happy to know that I've got a new truck on order. It's a 1 ton cummins because I'm pulling 7000 pounds and I'm afraid my current a$$ end is gonna disintegrate 10 years from now.

It's definitely an entertaining thread!

 

[IvoryHemi]

I don't think that 22% is correct. 3.92 is a 22% higher than 3.21, but i don't think it's a 1 for 1 for RPMs.

Yes it is with all else being equal (same gear, tire diameter, speed, etc)

 

[BowDown]

And when RPM's are 22% higher, it will cause less lugging/strain on the engine, all else being equal.

That makes the assumption that there is lugging and strain on the engine (with 3:21's) which there isn't

 

[BowDown]

exactly. Less wear/tear on the trans too

How so, once the clutches fully engage trans wear is done. Do the 3:92 geared trucks not utilize clutches in the trans?
Gear ratios don't increase or decrease trans wear

 

[HSKR R/T]

41 pages .... and yet you still missed it

To maximize towing, get 3.92
To maximize mpg, get 3.21
To rock crawl, get 3.92

But ... for towing the white elephant in the room is that you still won't "need" the 3.92, because you are payload limited. Since we all (probably) use our truck for much more than just towing (heavy towing usually is just recreational in 1500's), then why waste extra fuel 95% of the time while not towing, when the 3.21 can save you gas AND tow at the same time, within the limitations of our payload?

The 3.21 just makes the most sense for our 1500s. There are some very select use cases for the 3.92, but most of the guys on this forum preaching about how badly we need the 3.92 don't actually need it and are just wasting gas. Each to their own.

And those preaching about gas mileage in a 1/2 ton truck don't realize the minute difference doesn't make that big of a difference long term. Basically just bragging rights. And most of those guys are probably also cheaping out running 87 octane instead of the recommended 89.

 

[Mountain Whiskey]

You 3:21 advocates just don't get it.

3:21 = usually drives a prius but wants to look cool buying flowers at Home Depot.

3:92 = wondering what the new shimmy in the wheel is only to find a prius stuck in the tire when parking at the dive strip bar.

Don't be that guy. Get the right gears. Flip that stripper an extra bill as you give her a pat on the rump and grab another cold one.

If you want flowers and gas milage, get a Tessla and burn some coal to charge it up.

 

[theblet]

“3.21 advocates”

 

[BowDown]

And those preaching about gas mileage in a 1/2 ton truck don't realize the minute difference doesn't make that big of a difference long term. Basically just bragging rights. And most of those guys are probably also cheaping out running 87 octane instead of the recommended 89.

You think 17-18 in the city vs 14-15 in the city is a minute difference?

 

[theblet]

damn right i run 87. It's designed for it. Manual clearly says use 89 for optimum performance. So 87 when not towing, 89 when towing.

 

[Buz]

That makes the assumption that there is lugging and strain on the engine (with 3:21's) which there isn't

You have to tow a 7,500lb trailer over the Rockies.
You have two Ram 1500's at home with the same 5.7 Hemi engine and transmissions.
One has a 3.21 rear and the other has a unique 2.62 rear.
Which one are you going to use to tow that trailer over the Rockies?