Towing

[dsherman26]

Those people saying shifting down a gear will increase strain on the transmission are making up stuff and calling their ideas "physics".

Not making anything up at all, and has nothing to do with shifting down a gear. If you're going up a hill, towing a load, it requires force between the wheels and the road to move. Where does that force come from? Torque applied through the driveshaft through the differential gears. A 3.92 rear axle ratio reduces the rotational speed of the driveshaft by a factor of 3.92, and torque applied from the driveshaft increases by a factor of 3.92 to drive the wheels. Yes, physics can back me up on that. So, if you have a 3.21 rear axle, same concept, except now, it's going to require additional torque from the driveshaft and the transmission to get the same amount of torque at wheels. Sure, you can downshift a gear so the engine is better matched to keep things moving, but it doesn't change the fact that if you're towing a full load up a hill at highway speeds, the lower 3.21 ratio will need more torque (albeit a lower driveshaft speed) from the driveshaft compared to the 3.92.

If you want to try debating the physics of it, go ahead. My degree may be in electrical engineering, but I still did quite well in physics, dynamics and statics. Still had to know those things to take the professional engineering exams to get my license.

 

[18CrewDually]

Not making anything up at all, and has nothing to do with shifting down a gear. If you're going up a hill, towing a load, it requires force between the wheels and the road to move. Where does that force come from? Torque applied through the driveshaft through the differential gears. A 3.92 rear axle ratio reduces the rotational speed of the driveshaft by a factor of 3.92, and torque applied from the driveshaft increases by a factor of 3.92 to drive the wheels. Yes, physics can back me up on that. So, if you have a 3.21 rear axle, same concept, except now, it's going to require additional torque from the driveshaft and the transmission to get the same amount of torque at wheels. Sure, you can downshift a gear so the engine is better matched to keep things moving, but it doesn't change the fact that if you're towing a full load up a hill at highway speeds, the lower 3.21 ratio will need more torque (albeit a lower driveshaft speed) from the driveshaft compared to the 3.92.

If you want to try debating the physics of it, go ahead. My degree may be in electrical engineering, but I still did quite well in physics, dynamics and statics. Still had to know those things to take the professional engineering exams to get my license.

Thankfully a 3rd person that gets it.
Like I said if the argumentative guy(s) don't get in the other posts by now then there's no help.
No one said anything about "grenading" but him. My messages were as clear as I could be. Go back and read with an open mind. He is missing the message.
Good luck all.

 

[yrraljguthrie]

Torque is not produced nor changed by the transmission. A transmission in 8th gear with the 3.92 has the same or close to the same numerical coefficient as if the transmission were in 7th gear with the 3.21. Sifting the transmission does nothing to change the amount of torque that reaches the rear wheel. A transmission is passive, it changes the ratio in the same way that a change in rear axle does. The reason for having a transmission is to allow the engine to increase or decrease its rpm. If a certain amount of torque from the engine is required to drag a trailer up a slope a certain amount of torque is required from the engine. So if the amount of torque is generated by the speed of the engine with a certain ratio of transmission and axle is possible the truck goes up the hill. If one reduces the numerical ratio of the axle then the transmission has to increase it's ratio of in to out. So a transmission in 8th gear and 3.92 axle is the same or close to the same as a transmission in 7th gear with a 3.21 gear. No change in power or torque. What happens is that the transmission changes the first ratio the engine sees and allows the engine to operate easier. A little like a bicycle. You're the engine, going up a hill you shift down and use the same number of pedal turns and you can go up the hill. The bicycle gears are actually under less stress and so is the engine...you.

 

[yrraljguthrie]

By the way, I'm getting old and arthritic and in pain all the time, don't feel sorry, I don't. BUT I do make small mistakes with numbers and words sometimes. But not usually with theory. So if you pick my posts apart you may find inconsistencies in details.

 

[Randy Grant]

12300 was wrong, nice of you to point that out. That doesn't change my intent. There is just very little difference between the 3.21 and the 3.92 performance-wise because the transmission can be shifted down one gear.

Just for ****sandgigles, this is my 2019


2019 Ram 1500 Limited
VIN.
5.7 e-Torque
3.92
Ivory
Mirror Cover, Right - Mopar (68263392AA) in black
Gross Axle Wt Rating - Front3700 lbs 3700.0 min 3700.0 max
Gross Axle Wt Rating - Rear4100 lbs 4100.0 min 4100.0 max
Curb Weight - Front2886 lbs 2886.0 min 2886.0 max
Curb Weight - Rear2078 lbs 2078.0 min 2078.0 max
Gross Vehicle Weight Rating Cap6900 lbs 6900.0 min 6900.0 max


LOOK UP MY VEHICLE
Look up towing and payload for a specific vehicle
Step 4 of 4
2019

VIN Or Year -
Vehicle - 2019 Ram 1500 Limited
Options - All
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2019 RAM 1500 LIMITED CREW CAB 4X2 5'7" BOX
8-Speed Automatic 8HP75 Transmission
Vehicle images shown may not reflect the selected model year. See dealer for details.

MAX PAYLOAD - 1367.74LBS

MAX TOWING - 11467.74LBS

Theoretically I could cross the scale at a little over 18k as long as I dont overload the rear axle.
But I don't, and I drive under 65.

 

[ramffml]

Not making anything up at all, and has nothing to do with shifting down a gear. If you're going up a hill, towing a load, it requires force between the wheels and the road to move. Where does that force come from? Torque applied through the driveshaft through the differential gears. A 3.92 rear axle ratio reduces the rotational speed of the driveshaft by a factor of 3.92, and torque applied from the driveshaft increases by a factor of 3.92 to drive the wheels. Yes, physics can back me up on that. So, if you have a 3.21 rear axle, same concept, except now, it's going to require additional torque from the driveshaft and the transmission to get the same amount of torque at wheels. Sure, you can downshift a gear so the engine is better matched to keep things moving, but it doesn't change the fact that if you're towing a full load up a hill at highway speeds, the lower 3.21 ratio will need more torque (albeit a lower driveshaft speed) from the driveshaft compared to the 3.92.

If you want to try debating the physics of it, go ahead. My degree may be in electrical engineering, but I still did quite well in physics, dynamics and statics. Still had to know those things to take the professional engineering exams to get my license.

What you're missing: the trucks aren't in the same transmission gear at the same mph.

final gear ratio = transmission gear * rear axle ratio

When 3.21 is in 6th:
transmission gear ratio = 1
axle ratio = 3.21
final gear ratio = 1 * 3.21 = 3.21

When 3.92 is in 7th
transmission gear ratio = 0.82
axle ratio = 3.92
final gear ratio = 0.82 * 3.92 = 3.2144

Those 2 trucks have absolutely identical torque multiplication; for every 3.21(44) rotations of the engine, the axles rotate once.

If you want to play an engineer, you should study the chart below. It shows the RPMS both trucks will be at when they're at 65 mph. Note the blue squares, these trucks are with 3 rpms of eachother because they are using the same final gear ratio.

 

[ramffml]

Thankfully a 3rd person that gets it.
Like I said if the argumentative guy(s) don't get in the other posts by now then there's no help.
No one said anything about "grenading" but him. My messages were as clear as I could be. Go back and read with an open mind. He is missing the message.
Good luck all.

A third person that doesn't get it. An you most certainly brought in the "stress" argument back in post #17 or have you forgotten what you wrote already? You didn't use the word "grenade" but obviously that's your argument below, that the increased stress can cause issues (damage/destroyed).

The 3:21 ring & pinion ratio increases load and stress on drivetrain from the rear axle U-joint all the way forward to the crankshaft, in comparison to 3:92s.
There's no way around that whether its 4, 5, 6, 7, 8, or 10 spd.
It's a gamble that may not be negligible.

And yet you haven't given any proof that the 3.21 can't handle the stress of towing 11,500 pounds, as I said the engineers may have engineered it for 15,000 pounds, we don't know. What we know is that the j2807 penalizes it due to 0 to 30 acceleration only, it doesn't test for driveline stress or wear and tear of any kind.

 

[18CrewDually]

A third person that doesn't get it. An you most certainly brought in the "stress" argument back in post #17 or have you forgotten what you wrote already? You didn't use the word "grenade" but obviously that's your argument below, that the increased stress can cause issues (damage/destroyed).



And yet you haven't given any proof that the 3.21 can't handle the stress of towing 11,500 pounds, as I said the engineers may have engineered it for 15,000 pounds, we don't know. What we know is that the j2807 penalizes it due to 0 to 30 acceleration only, it doesn't test for driveline stress or wear and tear of any kind.

Read back my other post. I specifically said longevity. I mean, remember the Toyota commercial towing the space shuttle? A truck towing over weight with 3:21s will cause more stress than 3:92s. It's pretty simple.

 

[ramffml]

Read back my other post. I specifically said longevity. I mean, remember the Toyota commercial towing the space shuttle? A truck towing over weight with 3:21s will cause more stress than 3:92s. It's pretty simple.

You used the word "stress" and now "longevity". What the heck do you think I was refering to when I said "grenade"? Dude....

You're taking a fact which is true in theory (stress) and simply waving it into the argument and asserting that the 3.21 will be a problem towing extremely heavy. That is a logical jump that you have failed to prove.

One part can be weaker than another part, and both of them can still be designed way stronger than needed for the task. This is what you're intentionally failing to admit.

As I said, the 3.21 could very well be engineered to tow 15000 pounds all day every day and still outlast the rest of the truck. We simply don't know. And what's more, we have 0 reports of the 3.21 causing issues while towing.

And that circles back to the argument that NEITHER truck is towing more than 8000 pounds without overloading the payload. The GCWR rating is not the limiting factor in our trucks, the payload is.

 

[dsherman26]

What you're missing: the trucks aren't in the same transmission gear at the same mph.

final gear ratio = transmission gear * rear axle ratio

When 3.21 is in 6th:
transmission gear ratio = 1
axle ratio = 3.21
final gear ratio = 1 * 3.21 = 3.21

When 3.92 is in 7th
transmission gear ratio = 0.82
axle ratio = 3.92
final gear ratio = 0.82 * 3.92 = 3.2144

Those 2 trucks have absolutely identical torque multiplication; for every 3.21(44) rotations of the engine, the axles rotate once.

If you want to play an engineer, you should study the chart below. It shows the RPMS both trucks will be at when they're at 65 mph. Note the blue squares, these trucks are with 3 rpms of eachother because they are using the same final gear ratio.

View attachment 524616

Sigh. I'm not missing that the transmissions are in different gears at the same speeds at all, I'm very much aware of that. As 18CrewDually and I are aware, you're still not quite getting what we're trying to get across. THE TORQUE AT THE DRIVESHAFT is higher with the lower axle ratio. Sure, if the transmission is in a different gear the engine RPM might be in the same ballpark and the overall gear ratio might be about the same, but guess what? Gearsets in the transmission are having to take the additional torque. Correspondingly, the engine/transmission combination is turning the driveshaft, so what has to counteract that torque? Motor mounts.

Your argument that we don't know if a 3.21 could tow the same maximum theoretical load as a 3.92 is valid, maybe it can and all would be fine. Your information on the acceleration times being the determining factor for the towing capacity for the two axle ratios is interesting, that's good to know. We're just trying to point out that saying there's no difference towing with a 3.21 in a lower gear is not at all accurate.

 

[ramffml]

Sigh. I'm not missing that the transmissions are in different gears at the same speeds at all, I'm very much aware of that. As 18CrewDually and I are aware, you're still not quite getting what we're trying to get across. THE TORQUE AT THE DRIVESHAFT is higher with the lower axle ratio. Sure, if the transmission is in a different gear the engine RPM might be in the same ballpark and the overall gear ratio might be about the same, but guess what? Gearsets in the transmission are having to take the additional torque. Correspondingly, the engine/transmission combination is turning the driveshaft, so what has to counteract that torque? Motor mounts.

Your argument that we don't know if a 3.21 could tow the same maximum theoretical load as a 3.92 is valid, maybe it can and all would be fine. Your information on the acceleration times being the determining factor for the towing capacity for the two axle ratios is interesting, that's good to know. We're just trying to point out that saying there's no difference towing with a 3.21 in a lower gear is not at all accurate.

Obviously there is a physical difference. There is no difference that matters towing with the 3.21 in 6th vs 3.92 in 7th.

And again, you're so worried about drive train stresses - I'd rather tow sustained in 6th gear/direct drive vs 7th/overdrive in the 3.92. Yet another point in favor of the 3.21.

Motor mounts? You guys are just nuts at this point, sorry. Hop into the real world please, many of us tow heavy with the 3.21.

 

[Wild one]

Some of you guys are just gonna have to " Agree to Disagree ",lol.

 

[ramffml]

I've on this forum for a few years, I've argued this position for those same years, and I thought I heard all the excuses and theories out there.

But then he just casually dropped the "motor mounts" thing in there and I'm sitting here wondering what I'm doing with my life.

Guess I'm heading for the ole exit sign on this thread too.

No offense to anyone in this thread, peace out!

 

[Randy Grant]

Those people saying shifting down a gear will increase strain on the transmission are making up stuff and calling their ideas "physics".

Tell that to a heavy hauler. That's why semis have a 13 speed tranny and pickups gave up the old tried and true four speed.

 

[dsherman26]

Motor mounts? You guys are just nuts at this point, sorry. Hop into the real world please, many of us tow heavy with the 3.21.

Ah, I see you must not have had my real world experience of helping dad replace the right front motor mount (multiple times, I might add) on an '83 GMC van that was cursed with the 6.2 diesel. Funny how the right front on that one is the one that takes the combined weight of the engine AND the torque moment. No doubt towing a 4300 pound Lincoln on a few cross country moves contributed to those failures.

Yeah, I must be nuts and I need to hop in the real world for even considering the motor mounts. Silly me! Have a nice day.

 

[Wild one]

Ah, I see you must not have had my real world experience of helping dad replace the right front motor mount (multiple times, I might add) on an '83 GMC van that was cursed with the 6.2 diesel. Funny how the right front on that one is the one that takes the combined weight of the engine AND the torque moment. No doubt towing a 4300 pound Lincoln on a few cross country moves contributed to those failures.

Yeah, I must be nuts and I need to hop in the real world for even considering the motor mounts. Silly me! Have a nice day.

I'm not getting involved in this discussion,but a little tidbit for you there's a few 800+ and a couple 1100+ rwhp trucks running around still using the stock truck motor mounts.The trucks motor mounts are pretty robust.If your Dad had been on the ball he could of chained the motor down in his old van and never had any issues with the motor mount.It was a common mod back in the day.BTW it's the left/drivers side mount that takes the load,open the hood and watch which way the motor rocks when you floor the skinny pedal

 

[dsherman26]

BTW it's the left/drivers side mount that takes the load,open the hood and watch which way the motor rocks when you floor the skinny pedal

Well, the tin worm retired that old van many moons ago, but here's a video of a GM 6.2 diesel. Dad wasn't wrong, it's the right front that took the load.

https://www.youtube.com/watch?v=KE0R60tZ-fc

 

[Wild one]

Well, the tin worm retired that old van many moons ago, but here's a video of a GM 6.2 diesel. Dad wasn't wrong, it's the right front that took the load.

https://www.youtube.com/watch?v=KE0R60tZ-fc

Put a load on the engine,and the pulling forces move to the other side of the engine.If you go out and floor the engine in your truck,it rocks to the pass side,and the pulling force tries to pull the drivers side mount apart. The engine turns counter clockwise,so the pulling force acts in the opposite clockwise direction.Even an engineer should be able to figure that out,lol. Doesn't matter which mount your dad had to replace,if he'd of chained the engine down,he wouldn't of had to replace the mount

 

[dsherman26]

Put a load on the engine,and the pulling forces move to the other side of the engine.If you go out and floor the engine in your truck,it rocks to the pass side,and the pulling force tries to pull the drivers side mount apart. The engine turns counter clockwise,so the pulling force acts in the opposite clockwise direction.Even an engineer should be able to figure that out,lol. Doesn't matter which mount your dad had to replace,if he'd of chained the engine down,he wouldn't of had to replace the mount

You are correct, the left front gets pulled up, but I already knew that. However, the torque counteracts the engine weight so the left front wasn't getting ripped apart but rather having the weight of the engine removed from it. As one would expect, that's not the one that kept failing. Right front has the torque adding to the weight, and surprise, surprise, that's the one kept failing! Sorry, the owner's manual made no mention of having to add a chain to keep the motor mounts from failing.

 

[crash68]

I'm not getting involved in this discussion

Huh?? ... LOL

Apparently rear end gear ratio doesn't matter but if an exact clone of your truck was made and had 3.21 gearing and your truck has 3.92 gearing... Which one would you want to be behind the wheel of in a race to the next stop light(0.4km away) from a 30 roll??