Unhappy with 1500 towing. Need Help

ramffml said:

I'm not discrediting the 3.92. See this post:

Unhappy with 1500 towing. Need Help

So then tell us…. If what you say is so true It's not "if", it's not my opinion, it's a mathematical certainty. The two trucks have a different tow rating on paper, due to the 3.92 being able to accelerate faster from a dead stop. Two of the J2807 tow rating tests deal specifically with 0...

www.ramforum.com

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Then why did you start off with your first post pretty much saying that all of us that have the 392‘s are basically full of crap when we said that the OPs high geared rear end is the problem?

ramffml said:

My entire argument in this thread has been this: the 3.21 and the 3.92 will give you identical towing results at 62 mph (which is what the OP talked about in the very first post) so for the OP, getting a 3.92 will not change or help him at 62 mph.

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So then again if the high gears and the low gears will yield the same towing results then why have two different ones? Maybe if the OPs truck had the 392 gears he could actually drive the speed limit where it was 65 or 70 without working the heck out of his truck.

corneileous said:

Then why did you start off with your first post pretty much saying that all of us that have the 392‘s are basically full of crap when we said that the OPs high geared rear end is the problem?

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I didn't say you're full of crap. I said the 3.92 won't fix the OP's problem (which is occurring at 62 mph) and he will have identical results at 62.

corneileous said:

So then again if the high gears and the low gears will yield the same towing results then why have two different ones? Maybe if the OPs truck had the 392 gears he could actually drive the speed limit where it was 65 or 70 without working the heck out of his truck.

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You're not reading what I'm writing. The 3.92 and 3.21 have different results towing at 0, but have the same results towing at 62 mph.

The mph at which we're comparing the two gears matters.

corneileous said:

OK so, after thinking about it, let me put it this way; the eight speed transmission is the only reason why you even have an argument in the first place but still, the 392 gear is much better for towing and the 321 is meant for people who don’t tow lot or at all or very light and want a 400 horse V-8 to get around 20 miles to the gallon when they’re not towing anything oh so don’t act like the 321 is all that and a sack of peanuts and pretty much discredits the 392.

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I guess it comes down to the Original posters main concern, Truck revs to 2700 rpm towing at 62mph or that it will only tow his trailer in 5th gear at 62 mph.

392,s would let him tow 62mph in 6th gear but he would still be turning 2700 rpms.

I guess the other advantage for him would be essentially he would get one more gear ratio when he tows,(1st-6th instead of 1st-5th) along with better acceleration from stop, but not worth changing trucks over in my opinion.

When we first started camping I towed a trailer about his size with a 99 Ram with a 5.2L 3:55 gears 46RH trans. Talk about a miserable experience.
On steep hills it couldn't maintain 50 mph in 3rd, if you crowded it to much it would shift to second and you still couldn't go over 50 as you were up against the rev. limiter.

Most people don't realize how good they have it with newer trucks

ramffml said:

I'm not discrediting the 3.92. See this post:

Unhappy with 1500 towing. Need Help

So then tell us…. If what you say is so true It's not "if", it's not my opinion, it's a mathematical certainty. The two trucks have a different tow rating on paper, due to the 3.92 being able to accelerate faster from a dead stop. Two of the J2807 tow rating tests deal specifically with 0...

www.ramforum.com

My entire argument in this thread has been this: the 3.21 and the 3.92 will give you identical towing results at 62 mph (which is what the OP talked about in the very first post) so for the OP, getting a 3.92 will not change or help him at 62 mph.

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Not trying to pick a side, just trying to learn. My question is...if they are at the same rpm at 62 mph, just a different gear in the transmission based on the rear end gearing, wouldn't the 3.92 be running higher rpm at say 63, 64, 65 mph and so on?!?! Therefore, possibly making it feel stronger, or quicker?!?! Or would the rpms go up the same on either version??

KKBB said:

Not trying to pick a side, just trying to learn. My question is...if they are at the same rpm at 62 mph, just a different gear in the transmission based on the rear end gearing, wouldn't the 3.92 be running higher rpm at say 63, 64, 65 mph and so on?!?! Therefore, possibly making it feel stronger, or quicker?!?! Or would the rpms go up the same on either version??

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While the 3.21 is in 6th gear and the 3.92 is in 7th, they have almost identical gear ratios (3.21 vs 3.2144, so, lets just call it "equal"). Since they have equal gear ratios at that point, they will both have the same power from the engine and will accelerate just as easily in those 2 gears. They are literally "in the same gear" at that point, just using a different numerical value (6th vs 7th) for it.

corneileous said:

OK so then just like I asked the other guy; if the eight speed transmission makes up for the torque magnification then why is it the trucks with the higher rear end gears don’t have the full 10,000+ trailer towing capacity?

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That's a good question I've wondered that myself, maybe a hold over from the way they have always rated trucks? or they don't want people complaining their truck wont tow their trailer 62mph in 6th gear

I don't know.

They stop the truck on a grade. Then from a stop proceed up it.

The 3.92 is rated to move 3000 more lbs than the 3.21.

They also measure the ability to descend a grade using the fewest brake applications. 3.92 does better.

They also must maintain a certain speed up a certain grade with a certain lowest gear. 3.92 does it better.

392DevilDog said:

They stop the truck on a grade. Then from a stop proceed up it.

The 3.92 is rated to move 3000 more lbs than the 3.21.

They also measure the ability to descend a grade using the fewest brake applications. 3.92 does better.

They also must maintain a certain speed up a certain grade with a certain lowest gear. 3.92 does it better.

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I did not know that, thanks

Another question I always had was, With any transmission 1 to 1 is the most efficient ratio. least amount of power loss through the transmission, why do they make all modern transmissions with overdrives?
Why not make an 8 speed with top ratio 1 to 1 and put really high rear end gears? I asked that at school years ago and didn't get a good answer.
There must be a reason, I dont pretend to be a know it all Im always learning

yoda said:

I did not know that, thanks

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There is even more...but those are the 3 easiest to explain.

ramffml said:

While the 3.21 is in 6th gear and the 3.92 is in 7th, they have almost identical gear ratios (3.21 vs 3.2144, so, lets just call it "equal"). Since they have equal gear ratios at that point, they will both have the same power from the engine and will accelerate just as easily in those 2 gears. They are literally "in the same gear" at that point, just using a different numerical value (6th vs 7th) for it.

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At the speed quoted by the OP, I have to agree that changing the rear gear ratio should not be an improvement in rpm or noise or wear on the engine. Since some side issues have been raised by others, let's briefly consider what happens at other speeds. There seems to be agreement that torque in first gear is affected. What about 8th? When not towing, one might travel faster, and in 8th gear. A person doing that a lot might prefer the 3.21 because is will save gas in that situation. With the lower rpm's, there would be less noise and engine wear (as long as not physically lugging). All that might be the reality that causes someone to suggest that the 3.21 is better for someone who doesn't tow much. What about the difference in towing capacity? Individual components can and will break when overloaded. Even the driveshaft can break, as can individual gears. If we change the axle ratio and then the transmission changes accordingly, to get the same engine rpm, then some of the components in the drivetrain will experience different levels of stress, perhaps pushing some components closer to their limits. I am no expert, but that is my first guess at what might cause a change in towing capability when the axle ratio is changed. Also, I guess that at "direct" gear, there are more components that are subject to no stress at all, perhaps leading to longer transmission life. The discussion so far has implied that the transmission will indeed (at the speed discussed) end up with the same engine rpm with either axle ratio. That makes sense of course, but (and here I admit even more ignorance) in these days of electronic control, is it possible that a computer supervises the overall operation and second guesses the situation and instructs the transmission otherwise, knowing that the axle ratio is different?

ramffml said:

You're just writing stuff without any numbers or math to back your claims. Its no wonder you don't get it.

View attachment 487894

Lets do the math. A 3.21 in 6th gear has a gear ratio of 3.21. A 3.92 in 7th has a 3.2144 gear ratio.

Fact #1: When the 3.21 is in 6th gear, the engine RPMs and mph will be identical to the 3.92 in 7th gear.

Fact #2 Since the engine RPMs are the same, and the mph are the same, so is the torque/power.

Please point out which of those 2 facts you don't accept as true.

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Here are the correct ratios for Ram’s 8HP75 transmission

Bricknhank said:

Today I picked up my Grand Design Imagine 2600rb. I’m a first time RV’r. I was incredibly disappointed as to how the 75 mile ride home went. It was all expressway and mostly flat (It is Illinois) and my truck rarely made it out of 5th gear! My truck is a 2020 Longhorn with a towing capacity of 8120 lbs with a max payload of 1770lbs. 5.7 Hemi with e torque and 3:21 gears. 8HP75 transmission. The trailer weighs 5800lbs dry and since it was new there was nothing loaded in the trailer yet. I used a weight distributing hitch, Equal-I-Zer brand.

At 62mph (with everyone passing me) in a 70mph limit, the truck was revving at 2700rpm’s in 5th gear. I did use tow haul to enter the expressway but turned it off once speed increased. There were a few times on a slight downgrade that the transmission shifted into 6th gear and one time coasting it briefly went into 7th gear but it was brief. The Electronic Range Select (ERS) was not engaged. Upshifting and downshifting were fine.
I have never had any problems mechanically with this truck and up until today (with exception of some Rambox latch problems) I have loved this Longhorn. The 5.7 has always been a good runner for me.

So, please, I’m looking for suggestions from experienced RV’rs as to what is going on here? Is the 3:21 gear the culprit? Did Ram overstate the towing capacity? Just because the truck’s frame and axles can physically carry the weight, maybe the transmission isn’t equipped for towing. I’m leery to add the usual weight of daily necessities for a trailer trip let alone hitting any hilly areas. After at $70K for a truck and another $40K for the trailer it quite disappointing. I’m desperately seeking experienced analyses.
Thanks in advance,
Hank

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Your numbers are MAX towing NOT what your truck may be!!! You need to read the plaque on the t4uck. It is probably 6680 towing, 1500 load. Think your ratio is 3.21, should he the 3.92!

I have a 16 Big Horn with the 5.7 and 391 gears. My TT weighs about 8500 with gear. I have traveled thru Il. several times. I-39 down to I-24 east to Ky. Mine runs in 6th to 7 though mostly 6th. I limit speed to 65 & usually about 2200 rpm. Truck runs fine, no trans temp variations, still the same temps as empty. In prep I run 1000 over springs & air bags in the center of the springs pumped to 50 lbs. Sounds like you are doing pretty good. Fuel mileage goes to about 9-10 mpg though. I always get rid of eco by using the gear selector. Using tow/haul I believe increases trans pressure to help save clutches. I also set cruise control.

Bricknhank said:

Today I picked up my Grand Design Imagine 2600rb. I’m a first time RV’r. I was incredibly disappointed as to how the 75 mile ride home went. It was all expressway and mostly flat (It is Illinois) and my truck rarely made it out of 5th gear! My truck is a 2020 Longhorn with a towing capacity of 8120 lbs with a max payload of 1770lbs. 5.7 Hemi with e torque and 3:21 gears. 8HP75 transmission. The trailer weighs 5800lbs dry and since it was new there was nothing loaded in the trailer yet. I used a weight distributing hitch, Equal-I-Zer brand.

At 62mph (with everyone passing me) in a 70mph limit, the truck was revving at 2700rpm’s in 5th gear. I did use tow haul to enter the expressway but turned it off once speed increased. There were a few times on a slight downgrade that the transmission shifted into 6th gear and one time coasting it briefly went into 7th gear but it was brief. The Electronic Range Select (ERS) was not engaged. Upshifting and downshifting were fine.
I have never had any problems mechanically with this truck and up until today (with exception of some Rambox latch problems) I have loved this Longhorn. The 5.7 has always been a good runner for me.

So, please, I’m looking for suggestions from experienced RV’rs as to what is going on here? Is the 3:21 gear the culprit? Did Ram overstate the towing capacity? Just because the truck’s frame and axles can physically carry the weight, maybe the transmission isn’t equipped for towing. I’m leery to add the usual weight of daily necessities for a trailer trip let alone hitting any hilly areas. After at $70K for a truck and another $40K for the trailer it quite disappointing. I’m desperately seeking experienced analyses.
Thanks in advance,
Hank

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Sorry, your truck is a poor fit for a heavy un-aerodynamic travel trailer. It works, just don't expect a fully satisfactory experience. RPMs will be high and mileage low.

1. Always use Tow/Haul when towing. It prevents hunting and reduces strain on both the engine and transmission. This was part of your problem.
2. The 3:21 gear ratio is not ideal for this much weight. With that ratio, your truck will seldom use gears 7 or 8. With the 3.92 ratio your gears would have been higher, but it's likely that the engine RPMs would be nearly the same as what you are seeing now. The 3.92 ratio helps acceleration. You don't have it, so you need to drive like your truck doesn't have lots of acceleration.

I tow a 6,500 lb Grand Design travel trailer with a Ram 1500 BigHorn EcoDiesel Crew cab with a 3.92 axle ratio. Its rated for 1600 lbs payload and 11,000 tow weight. It holds 33 gallons of fuel, has more torque than the V8, at lower RPMs and gets better fuel mileage: between 12 and 15 while towing. The transmission only drops to 5 on very steep hills below 60. It runs in 7 and 8 over 65 on flats. It's a joy to drive long distances.

ramffml said:

if you're towing that load in 7th I'll be towing that same load in 6th (your gear ratio is 3.2144, mine is 3.21, they are literally identical gear ratios, see how the math works?)

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3.92 axle has a slightly lower gear ratio in 7th vs 3.21 axle in 6th

3.2928 vs the 3.21

bborzell said:

Several responses advise the OP to stay in tow mode with 3.21 diff. Is the same advise applicable for 3.92?

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Yesl

In the real world, while towing, I don't need more stoplight performance under WOT. I need passing/highway power, just like the OP, and that cannot be improved by using a 3.92.

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I think you should retract this statement....If you think that 3.92 won't tow better at higher speeds than 3.21's. You need to go back to whoever the math teacher was that told you and have him explain it better because you actually are not well informed.

My two cents.

IvoryHemi said:

Careful... payload on a diesel 2500 isn’t significantly higher than 1500

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So true, I have the same trailer(2600RB) and I had a 1500 (3.92), my payload was 1100ish and I was always at or a little higher than my payload number. The 2500 with the Cummins payload is around 1800 - 1900 (4x4 Laramies). Not enough to justify the price. I went with 6.4 + 4.10 and my payload is 2998, no more payload issues. IMO the 1500 can pull the weight just fine, it just has a limiting payload.

FasterZ Better said:

I think you should retract this statement....If you think that 3.92 won't tow better at higher speeds than 3.21's. You need to go back to whoever the math teacher was that told you and have him explain it better because you actually are not well informed.

My two cents.

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You may want to read the whole thread. Ramffml IS the math teacher and he’s correct.