3.21 vs 3.92 towing question

[Tazithman]

I have a 2020 bighorn 5.7 etorque 4x4 crew with the 3.21 gears. The tow rating listed for my truck is listed around 8100lbs. The same truck with 3.92 is listed at 11000 lbs.

My question is, couldn't the 3.21 truck just run a gear higher to make up the difference?

 

[silver billet]

When you do the math and calculate final gear ratio at the wheels, there are a number of gears which are either exactly equal (6 in 3.21 = 7 in 3.92) or quite close. But that is at the "top end".

When you get to first/second/third, there are no equals, and the 3.92 digs really deep in first gear.

So the advantage (and requirement for the 3.92) is due to getting off the line. The 3.92 can just go much lower, but once you're moving at city or highway speeds, there will be an almost identical gear match between the two, until the 3.92 reaches 8th at which point the 3.21 is in 7'th and has 1 more gear left (which it would probably never shift into while towing, it's meant for unloaded and high MPGs).

 

[Zeronet]

By far the biggest advantage of the 3.92 will be getting that load moving from a stop. The 3.92 will give 20% more torque at the wheels in first gear.

There may be other slight advantages in engine braking, having an additional usable gear and working the transmission a little less when towing. Slight.

Lots of good threads on here with detailed comparisons of the two gear sets.

 

[Willwork4truck]

I have a 2020 bighorn 5.7 etorque 4x4 crew with the 3.21 gears. The tow rating listed for my truck is listed around 8100lbs. The same truck with 3.92 is listed at 11000 lbs.

My question is, couldn't the 3.21 truck just run a gear higher to make up the difference?

You’ve got etorque which helps at the very beginning get the tires moving. If you are towing up at the max, your truck will still do it, just slower. I’d be more concerned with your payload as opposed to your gcvwr. The hemi, zf and 3.21 will pull a lot of trailer. What’s the expected terrain and speeds?
Can it stop it and can it carry the weight in the bed? Only you know what you are planning on towing.

 

[Tazithman]

Not really expecting to tow anything regularly other than a 7k camper. I do have to haul a 3500lb 2-car hauler on rare occasion and may push 11k lbs depending on whats on it (maybe once a year depending if I buy a new toy or something breaks).

I'm not one to go over max recommended weights but wanted to verify it as a matter of working the truck a little harder and not a matter of safety.

 

[ktl5005]

Not really expecting to tow anything regularly other than a 7k camper. I do have to haul a 3500lb 2-car hauler on rare occasion and may push 11k lbs depending on whats on it (maybe once a year depending if I buy a new toy or something breaks).

I'm not one to go over max recommended weights but wanted to verify it as a matter of working the truck a little harder and not a matter of safety.

What’s the gcwr of the vehicle? I’m sure a 7k camper already has you close to max gcwr before occupants and cargo

 

[brian42]

I'm not one to go over max recommended weights but wanted to verify it as a matter of working the truck a little harder and not a matter of safety.

Safety is staying within the published limits...GVWR, GCWR, and towing capacity.

The limiting piece(s) that drives those numbers is/are not necessarily the engine or transmission.

 

[OkieSooner94]

Safety is staying within the published limits...GVWR, GCWR, and towing capacity.

The limiting piece(s) that drives those numbers is/are not necessarily the engine or transmission.

You’re correct, Master Chief. The limiting factors here are the gear ratios and perhaps the suspension. Neither the engine nor the transmission would have an issue towing up to 12,750 lbs, when properly equipped, of course.

 

[JF19Longhorn]

Biggest factor on a 1/2 ton will be your payload.

I have the 3.92s and a 13XX lb payload.. with fuel, hitch weight, driver, and a 10-15% tongue weight, there is no way I can get close to that mythical 11,000lbs tow rating without going over the payload.

 

[mattee]

Biggest factor on a 1/2 ton will be your payload.

I have the 3.92s and a 13XX lb payload.. with fuel, hitch weight, driver, and a 10-15% tongue weight, there is no way I can get close to that mythical 11,000lbs tow rating without going over the payload.

I agree with this the most I think. People often overlook payload especially when camping because you ultimately load up the truck with lots of crap and you need to factor in all weight, towing and payload. That being said shorter gears will definitely help off the line but also at highway speed. In 1995 my dad bought a new 2nd gen Ram 1500 with the 5.9 liter gas engine and 3.55 gears (that was standard gear at the time),in 2010 I ended up getting a 2002 ram 1500 (which I just got rid of in April when I bought this truck), same 5.9 liter gas engine but with 3.92 gears and the big difference on the highway was down shifting my dad's truck would downshift with the slightest uphill grade almost like it was hunting for gears. Mine would rarely downshift, it would have to be a much, much harder grade to downshift. Now keep in mind both trucks only had 4 speed transmissions and the new transmissions are much better but when I was looking for a truck I waited to find one with 3.92 gears just because I didn't want any issues.
Just one man's opinion

 

[OkieSooner94]

Biggest factor on a 1/2 ton will be your payload.

I have the 3.92s and a 13XX lb payload.. with fuel, hitch weight, driver, and a 10-15% tongue weight, there is no way I can get close to that mythical 11,000lbs tow rating without going over the payload.

Payload is a myth. The axle rating is where it’s at. Get you some of these and you’ll be fine. 2009-Present RAM 1500 Timbren SES Suspension Enhancement System SKU# DR1500DQ - Rear Kit

 

[silver billet]

Payload is a myth. The axle rating is where it’s at. Get you some of these and you’ll be fine. 2009-Present RAM 1500 Timbren SES Suspension Enhancement System SKU# DR1500DQ - Rear Kit

Absolutely not. There are reports of cracked frames right above the Timbrens. You use those at your own risk especially while doing stupid and exceeding your payload.

 

[OkieSooner94]

Absolutely not. There are reports of cracked frames right above the Timbrens. You use those at your own risk especially while doing stupid and exceeding your payload.

Neither 8k lbs or 11k is gonna crack a frame, with or without Timbrens. Do you even now how exactly a truck’s max payload is determined?

 

[silver billet]

Neither 8k lbs or 11k is gonna crack a frame, with or without Timbrens. Do you even now how exactly a truck’s max payload is determined?

As I said there are reports of the Timbrens cracking the frame while towing within its rating. You can choose to ignore that, it doesn't change the facts.

 

[Rick3478]

I have a 2020 bighorn 5.7 etorque 4x4 crew with the 3.21 gears. The tow rating listed for my truck is listed around 8100lbs. The same truck with 3.92 is listed at 11000 lbs.

My question is, couldn't the 3.21 truck just run a gear higher to make up the difference?

Under most conditions, yes. But the tow rating includes things like being able to launch fully loaded from a dead stop up a 12% slope (that's from memory, so take with a grain of salt). Also, with 3.92 gears, the transmission, driveshaft, and u-joints operate at about 18% less torque for a given load, with the differential doing more of the gear reduction & torque multiplication work.

 

[Bt10]

As I said there are reports of the Timbrens cracking the frame while towing within its rating. You can choose to ignore that, it doesn't change the facts.

Can you provide any more info or links? I'd like to see that also. Thanks.

 

[silver billet]

Can you provide any more info or links? I'd like to see that also. Thanks.

There are some reports of this on the other forum. That's all I want to say as the mods don't really like links to that site.

 

[Rick3478]

As I said there are reports of the Timbrens cracking the frame while towing within its rating. You can choose to ignore that, it doesn't change the facts.

The sudden change in effective spring rate is what engineers like to call a step function. Step functions generate harmonics and other nasty side effects. I'd have thought the frame would bend before cracking, but if you hit it repeatedly fatigue may set in. They're cheaper than air bags and don't require a compressor or develop leaks with age, I guess you get what you pay for. As always, caveat emptor.

 

[Bt10]

Interesting. My GMC bumpstops were on the framerail, and if I remember correctly, the Ram is welded to the inside of the rail? Might be a good explanation for that problem. I've never seen it on this site, and it's drastically bigger than the other.

Timbrens are harder than the softest Sumos, and Sumo even recommends cutting a progressive taper on them if you are either riding them continuously or slapping them on minor bumps. A soft engagement probably solves most of that issue.