Sweet Spot for Cummins

['Lil Guy']

When towing the bigger rigs, is there a sweet spot to hold the RPM at? I've heard of between 19 and 2200 RPM. I guess it's because the torque comes in at 1800. With my 3.42 rear end, should I just keep the TV in a lower gear to maintain a good RPM. For instance, if towing, should you be in 5th gear? With my rear end, at 65 I'm at about 1500 RPM. Looking to be hauling a heavier load and don't want to lug the truck. Thanks in advance. Probably wouldn't be an issue with a 4:10 or 3:73 RE

 

[jnbhobe]

Just drive it the tranny will do what it's suppose to do. If there is a sweet spot you'll find it on your own, all trucks are different from one another.

 

[Bohemian]

Peak Torque

 

[hoefler]

On my 14 Ram, it likes 1750-1800 for cruising, when it does down shift, it only goes to 2000. On the 2010, it liked 2000-2100, when it down shifted, it went 2300.

 

[marvmarcy]

Its best to keep a loaded engine in the middle to upper portion of the torque curve. The sweet spot is for flat road cruising, but often not the best rpm for the load and conditions.

 

[Jim.Allison]

Tow/Haul mode delays shifting on terrain that is inducing frequent shifting. When cruising tow/haul primarily applies to 6th gear on the RAM transmission (and probably the other HD trucks). If it becomes obvious to you that your transmission is searching for a gear, then you should eliminate that shift point by dropping down a gear. In this manner you will be operating at the most efficient RPM. Diesels operate off of torque and it is very hard to lug these motors with as much torque that they are providing, its even more difficult to defeat the sophisticated motor and transmission controls. RAM states that you should set your cruise control and drive because it is not likely that you can improve the efficiencies of their systems. I find it to be true. But I also find that I have to sometimes drop down a gear because it is hunting/searching for a correct gear.

 

[Bohemian]

Tow/Haul mode delays shifting on terrain that is inducing frequent shifting. When cruising tow/haul primarily applies to 6th gear on the RAM transmission (and probably the other HD trucks). If it becomes obvious to you that your transmission is searching for a gear, then you should eliminate that shift point by dropping down a gear. In this manner you will be operating at the most efficient RPM. Diesels operate off of torque and it is very hard to lug these motors with as much torque that they are providing, its even more difficult to defeat the sophisticated motor and transmission controls. RAM states that you should set your cruise control and drive because it is not likely that you can improve the efficiencies of their systems. I find it to be true. But I also find that I have to sometimes drop down a gear because it is hunting/searching for a correct gear.

Exactly correct.

What does "peak torque" mean?

If motors were perfectly 100% efficient with 100% cylinder charge there would be no such thing as "peak torque". Torque would be a constant independent of rpm. The torque curve represents the varying efficiency of the motor. Peak torque is the maximum efficiency point of the motor.(under the torque test conditions).

HP, under perfect 100% efficiency with 100% cylinder charge , is a straight line starting with 0 HP at 0 rpm increasing linearly. It s proportional to fuel burned per second or energy consumed per second (power). If torque was an ideal constant, max hp would at max rpm.

 

['Lil Guy']

Do any of you use the cruise control when towing a heavier rig in tow haul mode?

 

[danemayer]

Do any of you use the cruise control when towing a heavier rig in tow haul mode?

We tow with cruise control quite a bit.

 

[jnbhobe]

If it's just a rolling terrain I use it all the time.I don't use it if it's up and down where it can't catch up at the bottom of a hill
.

 

[NWILSON]

The owner's manual on our '12 Ram says Tow/Haul locks out 5th and 6th gear. Mine does not! My "go to" guy says he knows the Aisin tranny locks out of 6th but not sure about the 68RFE tranny.
Yes, I tow with Cruise Control on all the time and will use the manual shift buttons on occasion.I suspect the EPA restrictions sometimes prevent shifts when "seat of the pants" driving says you need a different gear.

 

[hoefler]

Do any of you use the cruise control when towing a heavier rig in tow haul mode?

All the time.

 

[porthole]

The owner's manual on our '12 Ram says Tow/Haul locks out 5th and 6th gear. Mine does not! My "go to" guy says he knows the Aisin tranny locks out of 6th but not sure about the 68RFE tranny.
Yes, I tow with Cruise Control on all the time and will use the manual shift buttons on occasion.I suspect the EPA restrictions sometimes prevent shifts when "seat of the pants" driving says you need a different gear.

Locks out - or - locks up the converter?

Tow haul modes typically locks up the converter sooner and in lower gears, raises the transmission shift points (RPM) and increases line pressure to the clutches.


I use cruise almost all the time with the same exception Jon listed (short hills).

I tend to disengage the cruise when cresting hills (highways) to allow gravity to do some work. Since the Ford model years from 2011 - 2014 do not have any exhaust brake, they use aggressive transmission downshifting, to the point of being a bit annoying.

 

[NWILSON]

Duane....the owners manual says the transmission will automatically shift into overdrive gear (5th and 6th gears) if the Tow/
Haul switch has not been activated.
HOWEVER.......I just heard back from Ram Customer Service who checked with engineering regarding this statement. They said that the transmission will still shift into 5th and 6th in the Tow/Haul mode. Seems there may be an error in the owner's manual!