Figuring out best cruising speed

[Agewon]

Hoping you guys may give me some insight into figuring out my most efficient cruising speed.
I have a '14 GMC 2500hd with the Duramax and 3.73 gears. It's a crew cab and will mostly be occupied with about 450 lbs of humans and another 200+\- cargo. My trailer is a 3150bhd weighing at about 10k max.
Is there anyone out there with a similar set-up? Going to be mainly highway on the east coast, and PA can get pretty hilly, so I'll try and make up for that on the straights.

[Oaklevel]

I told the boys when I taught them to drive a stick the car will tell you when to shift....... I go by the same idea with speed pulling the trailer..... the truck kind of determines how fast but I rarely go over 65. I just go with what ever the MPGs are............ and don't worry about that.

[Chuckinca]

65 MPH works for me in most open highway flat situations.



.

[RKR]

No more than 65. Your Duramax will be in it's peak torque at just under 65.
Also, after 65 the wind resistance really kicks in and will effect you fuel mileage.

[Sirsea]

We like 62 mph on the open road, good for mpg plus most trailer tires are only rated for 65 mph.

[ependydad]

Originally Posted by Sirsea

We like 62 mph on the open road, good for mpg plus most trailer tires are only rated for 65 mph.

Same here.

[transamz9]

My truck really likes 70-72. Like others said, your tires on your trailer are rated at 65.

[AquaMan]

My 5er is around 14k and it likes 67-68mph. Anything less (62-65), and it feels like it's wanting to downshift, and occasionally does. Each trailer and setup has it's own "sweet spot", just need to find yours.

[Pipeman]

I run at 65 mph. It's in cruise and not in tow haul. I do use tow/haul for braking along with the engine braking. We travel across the top of the U.S. going out to western Canada and back the same way. In the foothills of the mountains and just about on any hilly roads we are in cruise and the duramax handles it great. Barely notice when it downshifts to 5th. I have a 2011, 1ton dually, crew cab, long box, 4x4. I use tow haul mode when merging back onto the highway to get up to speed. I've had 2 trucks with the duramax engine. The 1st one was a 2001 3/4 ton and I travelled at the same speed with that one but there is a ton of difference with the newer one. More HP for one. My 5er is 35 ft and when packed for camping and/or traveling out west the total weight for both vehicles is around 23,900 lbs. My tires all around are at 80 psi.

[Todouble]

Originally Posted by Pipeman

I run at 65 mph. It's in cruise and not in tow haul. I do use tow/haul for braking along with the engine braking. We travel across the top of the U.S. going out to western Canada and back the same way. In the foothills of the mountains and just about on any hilly roads we are in cruise and the duramax handles it great. Barely notice when it downshifts to 5th. I have a 2011, 1ton dually, crew cab, long box, 4x4. I use tow haul mode when merging back onto the highway to get up to speed. I've had 2 trucks with the duramax engine. The 1st one was a 2001 3/4 ton and I travelled at the same speed with that one but there is a ton of difference with the newer one. More HP for one. My 5er is 35 ft and when packed for camping and/or traveling out west the total weight for both vehicles is around 23,900 lbs. My tires all around are at 80 psi.

I've always heard you should use tow/haul mode when towing heavy. It provides engine braking and changes the trans shift points. Don't know for sure but was told you can tear up a tranny if you don't when towing heavy. Anyone else know what's correct?? Aside from that I run about 68 mph towing a 12k fiver!

[Pipeman]

Well I had the 3/4 ton for 10 years and this truck since 2011 and no problems at all. If in tow haul mode the transmission stays in gear longer to get up to speed. I do use it for braking along with the engine braking mode . That's my experience.

[Rrickim63]

Originally Posted by Todouble

I've always heard you should use tow/haul mode when towing heavy. It provides engine braking and changes the trans shift points. Don't know for sure but was told you can tear up a tranny if you don't when towing heavy. Anyone else know what's correct?? Aside from that I run about 68 mph towing a 12k fiver!

I've been told the same. It does use more fuel,but I was told the last thing you want is the transmission lugging at low rpm in overdrive. It increases temperature of fluid. Why else would manufacture s put a tow/haul mode on a truck if it wasn't meant to be used.

2006 roo 23b
99 Silverado xtra cab with 4.8 and tow package

[Old Bones]

Originally Posted by Todouble

I've always heard you should use tow/haul mode when towing heavy. It provides engine braking and changes the trans shift points. Don't know for sure but was told you can tear up a tranny if you don't when towing heavy. Anyone else know what's correct?? Aside from that I run about 68 mph towing a 12k fiver!

I was told the same thing with every truck we've had.

We've been towing between 90 - 100 KMph (55 - 62 mph). Run into sway issues, so still working on getting everything dialed in better.

We have friends that used live in the Canadian Rockies. When we'd go out to visit them, they had told me while traveling through the mountains even without a load, the truck should be in tow/haul as to not burn up the tranny.

[Todouble]

Originally Posted by Rrickim63

Why else would manufacture s put a tow/haul mode on a truck if it wasn't meant to be used.

Agree.... It's there for a reason, I use it. I'm not worried about saving a few pennies of gas when towing. It's only money and you can't take it with you as my father always said!

[Agewon]

I actually had someone tell me that the tow/haul mode will tear up your tranny faster. I'll try and get a reason and post back.
Does the engine brake only work in tow mode?

[AquaMan]

Originally Posted by Agewon

I actually had someone tell me that the tow/haul mode will tear up your tranny faster. I'll try and get a reason and post back.
Does the engine brake only work in tow mode?

It works in both modes, but has a bigger effect in the tow mode.

[RKR]

Originally Posted by Agewon

I actually had someone tell me that the tow/haul mode will tear up your tranny faster. I'll try and get a reason and post back.
Does the engine brake only work in tow mode?

You should have a T/H button on the console. My '11 is below the radio on the right. Just push the button in and when you touch the brakes it will activate the engine (jake) brake.
I don't see how the T/H mode will hurt your Allison. Besides the Allison being a beast I don't believe any manufacturer would put an option on a vehicle that would damage it.

[grayfox]

Originally Posted by Agewon

Hoping you guys may give me some insight into figuring out my most efficient cruising speed.
I have a '14 GMC 2500hd with the Duramax and 3.73 gears. It's a crew cab and will mostly be occupied with about 450 lbs of humans and another 200+\- cargo. My trailer is a 3150bhd weighing at about 10k max.
Is there anyone out there with a similar set-up? Going to be mainly highway on the east coast, and PA can get pretty hilly, so I'll try and make up for that on the straights.

Depends on what you want. These diesels seem to have a sweet spot. For me and my 05 2500 HD D/A it likes about 1800 RPM HWY, about 60-62 MPH as I like to drive for fuel economy. You just have to figure out what you want and explore at what RPM does it for you. I live in SW PA in the Alleghenies and travel the Shenandoah Valley often.

[RKR]

Allison/Duramax T/H article

http://ignoringthebarkingdogs.blogsp...whaul.html?m=1

[Brother Les]

You will find out your sweet spot. The truck and trailer will tell you. My old 29ft was at 72mph at 2100rpms. My current 35ft is 65mph at 1900rpms.

My truck easily pulls both at 80mph. But life is to short to have the stress level that high.

safety first and always.