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

[silver billet]

Very nice write up. I have the 2020 1500 Classic, 392 ( I mean to say 5.7 Hemi — confused as my first Hemi was the 392 hemi of my 1956 St Regis), 3.21, 2wd.

Towing my 5000 lb trailer seems best in 6th gear which I need to select manually, as the tow mode typically runs under or at 2000 rpm at 57 mph. Where can I find a torque curve for this setup? What would you suggest as the optimum cruising rpm As the cruise control selects 7th ?

Appreciate your insight.

I typically pull at 2300 RPMs or so, little more little less, but in 6th gear. My truck picks that gear naturally, but I do lock out 7th just because sometimes it might want to upshift for a few seconds.

So I put it in TH mode, and then use gear limiter to lock it down to 6th.

 

[KWKSLVR]

I typically pull at 2300 RPMs or so, little more little less, but in 6th gear. My truck picks that gear naturally, but I do lock out 7th just because sometimes it might want to upshift for a few seconds.

So I put it in TH mode, and then use gear limiter to lock it down to 6th.

How much weight do you pull?

 

[silver billet]

I believe the trailer is rated to 7500 pounds gross, but I don't always load it right up. Never weighed it, but I have to be over 5000 pounds anyway. For the most part, I can't really tell much difference in terms of weight, towing it empty vs loaded, maybe a bit off the line but I have to think its mostly wind resistance/drag that is the real issue on the freeway, it's a giant brick back there and no getting around that.

 

[Buz]

View attachment 100060

Tip:
Get rid of the 'AVE MPG' on your center screen, replace it with your speed and put the clock where your speed is now.
Your drives will be much more stress free. f I'm at 6k miles on mine and 12.6 is still considered good for my truck. Mostly around town.

 

[KWKSLVR]

I believe the trailer is rated to 7500 pounds gross, but I don't always load it right up. Never weighed it, but I have to be over 5000 pounds anyway. For the most part, I can't really tell much difference in terms of weight, towing it empty vs loaded, maybe a bit off the line but I have to think its mostly wind resistance/drag that is the real issue on the freeway, it's a giant brick back there and no getting around that.

I'm curious to see how little I'll be able to tow once mine comes in. As long as I can handle one of those smaller pull behind RV's, on occasion, I don't guess it matters all that much.

 

[silver billet]

I'm curious to see how little I'll be able to tow once mine comes in. As long as I can handle one of those smaller pull behind RV's, on occasion, I don't guess it matters all that much.

For sure, there are many trailers you'd be able to pull. The drivetrain isn't the week spot in our trucks, so you'll have enough power to pull 8000+ pounds, it's more about payload and keeping your tongue weight down.

Especially in your truck: Limited, etorque, ORG, ram box, 4x4, those are all heavy so I'd be careful and read your door jamb for payload specs.

Have to say I'm jealous of your 33 gallon tank though! I factory ordered my truck but missed that feature and really wish I had it.

 

[Mountain Whiskey]

I love how the thread starter for this thread is "I hope this post will help to end the debate". That's great!

 

[KWKSLVR]

For sure, there are many trailers you'd be able to pull. The drivetrain isn't the week spot in our trucks, so you'll have enough power to pull 8000+ pounds, it's more about payload and keeping your tongue weight down.

Especially in your truck: Limited, etorque, ORG, ram box, 4x4, those are all heavy so I'd be careful and read your door jamb for payload specs.

Have to say I'm jealous of your 33 gallon tank though! I factory ordered my truck but missed that feature and really wish I had it.

Yeah, I was explaining it all to my wife and I think she's a little disappointed, but I also wasn't going to buy a 2500 for something I might pull 1 or 2 times in the next 5+ years. For my use, the ram boxes are legitimately useful and I'm in a place in life where I want unnecessary creature comforts.

 

[Cliffrunner88]

Tip:
Get rid of the 'AVE MPG' on your center screen, replace it with your speed and put the clock where your speed is now.
Your drives will be much more stress free. f I'm at 6k miles on mine and 12.6 is still considered good for my truck. Mostly around town.

I definitely agree, lol

 

[Michaelpotter7518]

I don't tow so the 3.21 is fine for me getting 17 to 19 mpg

 

[Redfour5]

I definitely agree, lol

I had to take the Bighorn level 1 package and got the 3.5 "color" TFT EVIC. I had the 7 inch on my 2015. I did get the console and not the bench seats. I checked the EVIC out though and with the four analog guages, it shows everything my 2015 shows and I like analog guages being an old fart, so, I'm liking it. I had a 2013 with the 3.5 EVIC in black and white and it sucked in comparison, but the new color 3.5 is decent. I haven't used the trailer related stuff yet. I assume it will be OK also.

 

[Cliffrunner88]

I’m realizing my 90% city driving is killing my mpg far more than I thought it would. Sadly none of my drives are 70% highway

 

[neeginan]

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.

Not in my case. I only looked at trucks with the 3.92 because I knew I was going with larger tires and I didn't want to end up with an effective axle ration in the high 2's or ~3.0.

Assuming stock tire size of 275 55 R20 (or another ~32 in tire): If you have a 3.92 and go with 275 65 R20 tires, you will reduce your 3.92 to effectively a ~ 3.67. That's what I currently have.

Gear Ratio Calculator

Easy to use gear ratio calculator. Use our gear ratio calculator to find the correct gear ratio to run when changing tire sizes to keep your stock gearing.

tiresize.com

 

[carterashley]

Great information. get-vidmate.com instasave

 

[Scram1500]

Curious, is the 3.92 in a Rebel with 33 inch tires the same as the 3.92 in a standard 1500 with 32 inch tires? Is the Rebel really a 3.79?

 

[IvoryHemi]

Curious, is the 3.92 in a Rebel with 33 inch tires the same as the 3.92 in a standard 1500 with 32 inch tires? Is the Rebel really a 3.79?

Correct the Rebel’s 33” tires make the 3.92 effectively a 3.79 axle

 

[nc_beagle]

For sure, there are many trailers you'd be able to pull. The drivetrain isn't the week spot in our trucks, so you'll have enough power to pull 8000+ pounds, it's more about payload and keeping your tongue weight down.

Especially in your truck: Limited, etorque, ORG, ram box, 4x4, those are all heavy so I'd be careful and read your door jamb for payload specs.

Have to say I'm jealous of your 33 gallon tank though! I factory ordered my truck but missed that feature and really wish I had it.

I'm really hoping to one day see DTE 1000 miles when I fill up (diesel) but with a Limited, 3.92, and ORG, I doubt I'll ever get a high enough average.

 

[IvoryHemi]

I'm really hoping to one day see DTE 1000 miles when I fill up (diesel) but with a Limited, 3.92, and ORG, I doubt I'll ever get a high enough average.

You should still be able to get pretty close with the 3.0

Mine has shown a 686 mile range with the 5.7L/3.92

 

[hutchman]

Hhhh

 

[HSKR R/T]

Correct the Rebel’s 33” tires make the 3.92 effectively a 3.79 axle

It's still a 3.92. so, is the Rebel "effectively" a 3.79, or is the regular 1500 a 4.05?