Another 3.21 vs 3.92 comparison

[Cr250Ram]

I decided to make this post to share my extensive time and research into towing and axle ratios. My backstory; I didn’t know about axle ratios and ended up buying a Silverado with the dreaded, and all too common, 3.08 axle ratio. The BEST tow rating you could get was 6,100 pounds with 12,000 combined. It was horrible!!! Not only that but I learned the advertised “max tow” ratings are unattainable for how most people use their trucks. This lead me down a path of “enlightenment” about towing and I’ve learned A LOT. *this thread is about *legal* tow ratings, we all know the truck can exceed these ratings, however you run the risk of legal/civil liability and denied warranty claims when exceeding the ratings.

I recently ended up deciding to buy a 19’ Ram 1500 with the 3.21 axle ratio despite my past experience with the 3.08s. I am sharing my research on why the 3.21 ratio isn’t bad, compared to the 3.92, and WHY in most cases you will never even be able to access the additional towing ability with the 3.92s. Sure the 3.92s look good on paper with their “max trailer weight number”, but when you crunch the numbers it is really *only* better if you are driving solo with nothing else in your truck. This is due to the rams payload.

The chart below is a direct comparison of the 3.21 vs 3.92 ratio for MY SPECIFIC truck, and what I believe to be one of rams most common configurations, obviously other models (single cab) will produce much different results! If you look at the very bottom you will see what the truck is capable of towing with a family of 4 (600lbs) in the truck and NOTHING else in the bed.

***As you can see the 3.92 can really only tow 1,300 more pounds than the 3.21 when traveling with a family of 4, and ONLY if the trailers tongue weight is at 10%.**** This is due to the Rams payload of 1,505 pounds (configuration specific).

***The 3.92 and 3.21 have the SAME towing ability when towing at 15% tongue weight with people riding in the truck****

10% tongue weight is often only obtained with things like a boat.
Closer to 15% tongue weight is often encountered with heavier things such as cargo trailers and travel trailers. Those batteries and propane weight A LOT.

I hope this helps someone out there shopping. I WAS dead set on 3.92s until I got the same truck for $5,000 less but with 3.21s. I did the math below and discovered the 3.21s will work good for my individual needs. With this said the 3.92 will provide a more comfortable tow than the 3.21 even with the same weight, again this data strictly looks at legal ratings. Please tow safe so everyone can get to their destination safely. I am nervous for those I see towing 30’+ travel trailers at 8k+ with their half tons because “max tow” is over 10,000...

 

[Cr250Ram]

I highly recommend this site;
http://changingears.com/rv-sec-calc-trailer-weight-tt.shtml
You can input your own numbers and obtain your trucks towing capacity. Remember to add your trucks cargo (passengers and gear) to your trucks GVW when inputing the numbers!
*my personal 2 cents if you want to tow; buy a 19+ ram 2500 GAS 6.4. You get crazy good *legal* tow ratings (payload, hitch, trailer).

 

[troutspinner]

I'm not discounting any of your research and work. The math reveals the capabilities but the actual driving experience between the two gears is much different when towing heavy, even when not towing the 3.92 offers a better driving experience IMO.

The dealer just a couple miles away from me had the perfect truck, every option and color I wanted except it had 3.21 gearing. My wife and I sold our travel trailer so I no longer needed to tow heavy so I thought it would be easy to talk myself into that truck, heck, even save some gas but after test driving that truck, it just felt like a dog compared to my then 14 Ram with 3.92. The search continued with the 3.92 a must when I purchased.

 

[cotonymopar]

I just prefer the 3.92 gearing... if need it, more than if I want it...

 

[Cr250Ram]

I'm not discounting any of your research and work. The math reveals the capabilities but the actual driving experience between the two gears is much different when towing heavy, even when not towing the 3.92 offers a better driving experience IMO.

The dealer just a couple miles away from me had the perfect truck, every option and color I wanted except it had 3.21 gearing. My wife and I sold our travel trailer so I no longer needed to tow heavy so I thought it would be easy to talk myself into that truck, heck, even save some gas but after test driving that truck, it just felt like a dog compared to my then 14 Ram with 3.92. The search continued with the 3.92 a must when I purchased.

You are absolutely correct in regards to the driving experience. I also recognized that in my original post towards the end. I too required the 3.92 during my research, however the 3.21 feels way better than my 3.08s so it was an upgrade for me I wish you luck in your search for 3.92. I too preferred them to the 3.21s if not for the 5k savings.

 

[troutspinner]

You are absolutely correct in regards to the driving experience. I also recognized that in my original post towards the end. I too required the 3.92 during my research, however the 3.21 feels way better than my 3.08s so it was an upgrade for me I wish you luck in your search for 3.92. I too preferred them to the 3.21s if not for the 5k savings.

I found it back then. I am now at 1 year with my 19. I hear you on 5k savings for sure, hard to turn that down.

 

[Granite5thgen]

I wish ram offered a 3.55 for us guys in the middle

 

[riccnick]

Yup, this is being echoed across this forum, and many others, as the issue with modern half ton trucks isn't the towing capacity, it's the low payload capacity. Heck, even now, modern HD trucks can get down into the 1,500 lb or less range with their payloads as well, because that 1,000 hp diesel and limo cab with leather and moonroof take a lot of weight off the top of the payload ratings.

 

[Helmetface]

Yea, but 35's...

 

[Cr250Ram]

Yea, but 35's...

Very VALID point, and if 35" are for sure in someones plans, I would say the 3.92s are a must have!

 

[Gmoosevt]

I think the debate is simple: if your truck is multi-use and often a daily driver, and you tow stuff that is 5000# or under for boating or typical light weight travel trailers, then a 3.21 is fine, and you’ll get better gas mileage during the 90% of mileage when you probably aren’t towing. If you tow stuff greater than 5000#, then go for the 3.92... but if you are towing frequently, or for work, then a 2500 or 3500 is much more purpose-built for towing and carrying loads. Net: there is a reason that 1500’s and F150’s are called ‘Light Duty Trucks’. Too many customers think a light duty truck should be able to do anything... and the market-savvy manufacturers are jumping all over that - by stretching the truth about what their real world light duty trucks can actually do, especially a crew cab with people on-board and gear in the box... exactly as the previous blogger pointed out. I just took delivery of a crew cab Laramie with a 3.21, and it tows my boats, 4500 lb travel trailer, and 3000 lb rated utility trailer just fine. It stickered for just under $64k, and I got it for $46k, by waiting (patiently) for a year and taking delivery on 6/31... which is also the best timing for any purchase of a model year ending truck. FYI, I left off the bagged suspension and city-slicker auto running boards... since they won’t work within 5 years on salt-laden upper Northeast roads.


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[Willwork4truck]

Bigger tires = 3.92
Racing = 3.92
Towing anything more than 5k wet probably = 3.92
Just out “having fun” = 3.92

Old grandpa driver never having a v8 that had more than 210 hp = 3.21
What was on the lot that the wife wanted color wise = 3.21
Don’t tow anymore (compared to 20 years ago) = 3.21
The 8 speed tranny vs the old days 3 and 4 speeds = 3.21

 

[Willwork4truck]

I think the debate is simple: if your truck is multi-use and often a daily driver, and you tow stuff that is 5000# or under for boating or typical light weight travel trailers, then a 3.21 is fine, and you’ll get better gas mileage during the 90% of mileage when you probably aren’t towing. If you tow stuff greater than 5000#, then go for the 3.92... but if you are towing frequently, or for work, then a 2500 or 3500 is much more purpose-built for towing and carrying loads. Net: there is a reason that 1500’s and F150’s are called ‘Light Duty Trucks’. Too many customers think a light duty truck should be able to do anything... and the market-savvy manufacturers are jumping all over that - by stretching the truth about what their real world light duty trucks can actually do, especially a crew cab with people on-board and gear in the box... exactly as the previous blogger pointed out. I just took delivery of a crew cab Laramie with a 3.21, and it tows my boats, 4500 lb travel trailer, and 3000 lb rated utility trailer just fine. It stickered for just under $64k, and I got it for $46k, by waiting (patiently) for a year and taking delivery on 6/31... which is also the best timing for any purchase of a model year ending truck. FYI, I left off the bagged suspension and city-slicker auto running boards... since they won’t work within 5 years on salt-laden upper Northeast roads.


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What? You mean my city slicker air cooled leather seats 1500 isn’t the very best thing to tow a 35’ 5th wheel or bumper pull trailer that completely maxes out my measly payload? Who’d have thought?

 

[SpeedyV]

What? You mean my city slicker air cooled leather seats 1500 isn’t the very best thing to tow a 35’ 5th wheel or bumper pull trailer that completely maxes out my measly payload? Who’d have thought?

Careful...you can get a "city slicker air cooled leather seats" 2500 or 3500 nowadays

 

[Gmoosevt]

Ha ha... I absolutely went for the the air-cooled seats and every other amenity inside the truck! ..and all the safety stuff too, which I love. It’s the ‘subject-to-fail’ unnecessary techno-stuff hanging on the outside that only a city-slicker would be willing to pay for. For 6 months out of the year I have snow or mud up to the running boards anyway. In reality, all the new trucks - Fords, Chevys, Rams - are good trucks - they all have good drive trains and they all can haul and tow almost everything that most of us need. The BIG and main difference that makes the Ram the far-and-away best truck for 2019 is the ride, the quietness, and the interior. And if you think about it, ALL your time with your truck is spent in the interior, driving it. Because of that, I ignore all the loading, towing, and ‘my truck looks better than yours stuff’ - and I only go by how it feels when driving it, and how much I like to drive it. And right now, the Ram product line is kicking all the other manufacturers butts in that regard.


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[Willwork4truck]

Careful...you can get a "city slicker air cooled leather seats" 2500 or 3500 nowadays

Yep, saw a 2500 limited 6.4 on I-35 S just today...

 

[cipherbreak]

Well I knew I was going to put 35s on my truck so the 3.92 gears were a hard requirement.

 

[mass-hole]

The one thing you are not taking into account here is tractive effort, which is the force that needs to be applied to the road to move the truck and trailer down the road.

If you need 5000 lbs of force on the road to keep you moving at 70mph and you have a 32" tire, that means you are looking at needing 6,667 ft-lbs(5000 lb * 1.33' tire radius) of torque at the rear axle shafts.

If you have a 3.21 gear, that means the twist on the driveshaft before the axle needs to be 6,667/3.21 = 2077 ft-lbs

If you have 3.92's, that means you need 6667/3.92 = 1701 ft-lbs

So the entire driveline forward of the rear axle is contending with 22% more torque at any given moment when running 3.21's.

There is an arguement to be made that, despite the 8 speed offering enough ratios to pull whatever you want, the engine needs to works harder to do it and so does the transmission. Reliability, heat and other things can come into play regardless of whether you are maxing out the GCWR truck or not.

 

[Cr250Ram]

The one thing you are not taking into account here is tractive effort, which is the force that needs to be applied to the road to move the truck and trailer down the road.

If you need 5000 lbs of force on the road to keep you moving at 70mph and you have a 32" tire, that means you are looking at needing 6,667 ft-lbs(5000 lb * 1.33' tire radius) of torque at the rear axle shafts.

If you have a 3.21 gear, that means the twist on the driveshaft before the axle needs to be 6,667/3.21 = 2077 ft-lbs

If you have 3.92's, that means you need 6667/3.92 = 1701 ft-lbs

So the entire driveline forward of the rear axle is contending with 22% more torque at any given moment when running 3.21's.

There is an arguement to be made that, despite the 8 speed offering enough ratios to pull whatever you want, the engine needs to works harder to do it and so does the transmission. Reliability, heat and other things can come into play regardless of whether you are maxing out the GCWR truck or not.

This post wasn’t meant, and doesn't, imply the 3.21s are as good as 3.92s in regards to towing heavy loads. It was aimed at addressing LEGAL load ratings and being able to reach those ratings when taking payload into account. J2807 sets the testing for towing ability. Rams are J2807 compliant so their ratings are backed up for validity. The J2807 criteria is pretty strict about overheating and engine problems during the testing.
Are you saying the 3.21s are unable to pull their rated weight?

 

[Willwork4truck]

I think he just gave a technical response to why 3.92’s are easier on the truck when towing. Your seat of the pants buttmeter would likely say the same thing in a tactile way.
Here’s an old (2011) dieselstop.com thread on hills and gear ratios. The response pretty much summed it up succinctly:
“The change from 4.10 to 4.88 is not so much to lower EGT as it is to increase hp at a given speed in a given gear. The 4.88 compared to 4.10 will make the engine run at higher rpm, where it has more hp at a given speed in a given gear. Therefore, with more hp, it will be able to maintain speed for longer as the hill gets steeper. The truck with 4.10 will lose speed and have to downshift sooner, because it was running at lower engine rpm where there was lower hp.” End of quote

Course it all depends on your engine’s torque and hp curves, something I don’t have at my fingertips...