Dodge Cummins 2WD/4WD mechanical efficiency questions...

[slowmover]

I decided a few decades ago that unless I lived in a place the local law enforcement used 4WD, that it was only convenience with otherwise constant penalties.

2WD with IFS will be the better roadgoing vehicle versus beam front axle. And rack & pinion steering vs sloppy sector gear types makes for an entirely different truck. It is a distinctly better tow vehicle.

On my 3rd Gen CTD, to replace the limited slip with a Detroit TrueTrac would cover traction issues with also Bridgestone Duravis commercial service traction tires on the Drive Axle.

Most guys in oilfield service (hotshot) go back to 2WD. Roads there are temporary to the drilling rigs. Horrific, some days, after rain and a million pound move has been completed. The Class 8 trucks I drove in that enabled us to engage both Drive Axles and, if things were terrible, to lock the differential to crawl away.

I've tuned the suspension with FF/RR antiroll bars and Bilstein shocks. More is planned.

Steering, handling and brakes are what really matter. I carry pressure-treat 2x10x10 to park trailer, and occasionally, truck. Concrete, asphalt, gravel, etc, are not acceptable bases for longer-term parking according to the manufacturers. A few more pieces to get a rolling start isn't a burden. Just a dirty one, ha!

Look over truck specification carefully. The extremely short-lived "need" for 4WD is offset mightily by avoidance thereof and an occasional tow. I've had occasion to have a travel trailer towed out from mud less than once per decade.

.

[ThomCat316]

Looks like I've been convinced....

Just now had a mad-scientist moment, though:
Buy running CTD 4WD.
Buy crashed Nissan Leaf.
Remove 4WD transfer case, make truck RWD.
Remove front diff, insert Leaf motor.
Integrate demand controller with RWD driveline torque sensing.
Integrate regenerative braking.

Presto! Hill assist with regen charging!

Please, someone tell me I'm insane and should NOT do this....

[gumby79]

Your insane enough to try it I was thinking hook a power head to the front output on the t-case. To charge as a series/peralel hybrid then then when battery is full throw the trans in N and go full 4wd eletric fwd or rwd. Would bring new meaning to the turm pulse and glide... in self propelled genset mode the motor /generatorwould be set to max out the fule curve. Any HP that was not needed to maintain speed would be dumped into the battery. Fallowed with a shut down , then glide till the battery needs charged in an hour 20-30min towing.
also this presurves the 2 low for tight trailer maneuvering and better control on ice.

[slowmover]

Is it a toy, or something on which you and your family will depend?

Will it "save" you $500 or $5000 in a calendar year AFTER you've recouped the cost?

A fifth wheel travel trailer looks nice on paper. But it uses up the trucks cargo capacity for volume and weight.

Over on Airforums are some threads by "Skatiero" where she and her husband beautifully modded a 29 and then a 32 foot Airstream to accommodate their family of nine.

Something like this with a well-chosen passenger van is far more "fuel efficient" than a specifically high mpg rig.

Where the trailer has been "maximized" in terms of not needing outside supply where X people over Y nights is concerned, is the path to take for fuel efficiency.

Trailer parked at given location and no use of the tow vehicle for ? days. That's the question to answer.

Limiting the use of an otherwise well chosen (and highly reliable) tow vehicle is the path to follow for reducing fuel burn. That limited use is then defined with carefully planned trips.

As I recently went over in a post on the thread "Economics of Modding" , it's not the highest mpg of the vehicle per se, it's the best use per mile.

A passenger van with short rear overhang and an indefinite lifespan aero trailer is a dynamically good as well as overall efficient package.

What I'm trying to say is that there is a limit to chasing FE in a specific instance.

[ThomCat316]

Originally Posted by slowmover

Is it a toy, or something on which you and your family will depend?

There are now two of us in the family full-time, with up to four additional for short visits. We are designing around this sort of scenario, both with the trailer and with the hauler.

Will it "save" you $500 or $5000 in a calendar year AFTER you've recouped the cost?

Net savings of going fulltime should be in excess of $10,000/yr. Cost estimate at this point is less than $20,000, based on a careful accounting of build costs and past experience with similar projects.

A fifth wheel travel trailer looks nice on paper. But it uses up the trucks cargo capacity for volume and weight.
Over on Airforums are some threads by "Skatiero" where she and her husband beautifully modded a 29 and then a 32 foot Airstream to accommodate their family of nine.
Something like this with a well-chosen passenger van is far more "fuel efficient" than a specifically high mpg rig.

We are looking at the capacity issue as more of a "transfer" to the trailer rather than a loss, and won't be really digging into the capabilities of the truck all that much. The weight budget for the trailer, loaded, increased when we decided to retire rather than vacation, which pushed us up from a Mercedes diesel FrankenDakota to the standard 5.9 CTD - but barely, as the trailer is coming in at a little over 3,000 lbs. with full tanks and stores. The Dakota would likely be up to the demand, but I'd rather have reserves in hand than live too close to the edge. If I were to put a 12V CTD in the Dakota, it would likely be perfect, but there are fully functional 2500s for sale all over the place.

Where the trailer has been "maximized" in terms of not needing outside supply where X people over Y nights is concerned, is the path to take for fuel efficiency.
Trailer parked at given location and no use of the tow vehicle for ? days. That's the question to answer.

We entirely agree with you in this, though we want the flexibility to boondock, bicycle about, carry kayaks to remote locations, haul loads, add a camper shell to the flatbed sometimes, tow a 32 ft. sailboat, and various other things that made a van a non-starter.

Limiting the use of an otherwise well chosen (and highly reliable) tow vehicle is the path to follow for reducing fuel burn. That limited use is then defined with carefully planned trips.
As I recently went over in a post on the thread "Economics of Modding" , it's not the highest mpg of the vehicle per se, it's the best use per mile.

True, given that specific target. Very much agreed. We are looking at this fairly holistically, and for various reasons are more comfortable with the pickup as the tow vehicle.

A passenger van with short rear overhang and an indefinite lifespan aero trailer is a dynamically good as well as overall efficient package.
What I'm trying to say is that there is a limit to chasing FE in a specific instance.

YES! Not our ideal solution for the two of us fulltiming, but a better one if we were planning to travel with kids or other passengers.

I haven't had a chance yet to go check out either "Economics of Modding" or the Airforums folks, and will, but I don't think, given the versatility we need out of a tow vehicle, that we're likely to change our plans. The focus will likely continue to be making the best of what we're working with.

Thank you for assigning additional reading, and for making me think more...

[ThomCat316]

Originally Posted by slowmover

I decided a few decades ago that unless I lived in a place the local law enforcement used 4WD, that it was only convenience with otherwise constant penalties.

Thank you for reinforcing what's been said about the lack of "need" for 4WD in almost all foreseeable scenarios. I think I'll go back with my first instincts and set it up as RWD, Torsen rear carrier, and pack a winch capable of lifting the truck and a few hundred feet of Dyneema miracle rope as an emergency backup.

[slowmover]

I looked at some of your older posts and saw I'd already asked the question about, "why build versus buy used?", previously in the trailer edge thread. (Might reference that before proceeding with this).

There's no real penalty in MPG with a CTD (Cummins Turbodiesel) with one trailer or type versus another given decent trailer aero qualities.

1) I've pulled the U-Haul 12x6x6 trailer twice over the same 700-mile roundtrip and seen 18-mpg with the combined rig just under 13k in weight.

And,

2) In the same climate & terrain (even some of the same road) pulled my 35' travel trailer and averaged 15-mpg. Combined weight is 17-18k. The rig is 63' OAL.

Solo, I average 24-mpg, and see 26/7 on occasion. This is simply setting cruise st about 1725-rpm or 58/9-mph. Same as when towing. (Truck weighs 7,940-lbs currently).

CTDs are fairly impervious to weight gains up to about 1k. Nothing at all like the penalty with gassers.

But it's a truck sure as hell overkill for a 3k trailer. In the oilfield I used a version of this truck to hotshot trailers in excess of 20k.

A one ton nearly always weighs over 6k, and it's expensive to move that mass. (Parts, component repairs, tires, etc).

Long acquaintance with all-aluminum aero trailers tells me there's no real advantage to low weight. A 6k 28' trailer isn't really any harder to move down the highway than a 4.5k 21'.

But the latter is FAR more "livable". Bigger capacities is king for RVs. For staying put and not having to run to town for supplies.

Sure, there's a limit to size vs. efficiency. But there's also a sweet spot:

A 12-13k pound combined vehicle is economical. Dead stock. (Given a turbodiesel drivetrain and motivated operator).

I'd like to recommend two things. To inform your thinking, not de-rail it.

I hate to see folks re-invent the wheel. To that end I first recommend perusal of Streamline & Silver Streak Trailer brands sales brochures from the 1960s. Some can be found on the Toms' Web Page website. There are Facebook pages with which I'm unfamiliar.

These manufacturers had Full time staff taking exquisite time to maximize space utilization. Capacities.

There are beautiful restorations of Airstream trailers available for viewing (the low end trailer of this type) over on Airstream Trailer & Motorhome Owners Community. But those renovations usually have compromises that negatively affect utility. It's very hard to get all of it right.

The space is so small that the penalty for missing the mark is huge.

I strongly favor buying used, and making sensible modifications in an overall sense (the least important RV system is the electrical . . but it's where folks go nuts today on solar electric. $$$ and questionable longevity). By overall I again reference

X people for Y nights without re-supply.

It's really the question to answer.

The truck you wish to have is now the penalty. A 3k aero trailer will not sufficiently reduce fuel burn substantially enough (over the above direction of renovation) to enable travelling greater distances on the same budget. M

Second,

Let me put this another way: rhetorically, when will circumstances "force" you from the RV to ordinary housing? Death is obvious, so is generalized paralysis (and other).

Weather (past mechanical breakdown and fire) is the most commonly cited reason. (Hail, tornadoes, extended sub-freezing, etc).

Temporary evacuation, extended, or permanent.

RV'ers (fulltimers, in that parlance) always need "an exit plan". Selling a CTD is usually easy. Selling an RV one will wait six months or more (and not at all in winter; it's an emotional purchase).

The farther advantage, therefore, of renovation versus new construction is ease of sale. There's always a buyer for the famous marques. Especially one where all systems are functional, leaks addressed, etc. Its an advantage that it's been out on the road.

As a corollary, the community (loosely) of fellow owners is not to be taken lightly. Not for practical reasons (repairs) or social.

I say all this (and more detail would append) as the choice of a CTD will likely cap MPG in the low twenties. That's as high as I'd go in guessing. It'd be impressive, but it's not 30+ as can be done with a different TV and trailer.

What I'm suggesting (context, not dissuasion) is that a quite comfortable and satisfactory road is already blazed thru the woods. You'd do it on less fuel, but all other concerns are basic to what's needed.

1) A one ton truck is a limiting factor
2) New construction usually takes years, and is fraught by compromise
3) Community of others not to be lightly dismissed
4) Eventual sale is part of ownership cost (which influences operational cost)

Fuel is usually less than 1/2 of daily expenditure. All other owner and operator costs will nearly equal it. THEN the cost of provisions and ground rent will exceed fuel on a per night basis.

A tool defines its use.

A CTD both gives and takes.

"We" usually recommend a buyer get the trailer first. It will determine the TV. By doing it the other way, the TT needs to be mated to the TV for full advantage.

.

[slowmover]

I looked at some of your older posts and saw I'd already asked the question about, "why build versus buy used?", previously in the trailer edge thread. (Might reference that before proceeding with this).

There's no real penalty in MPG with a CTD (Cummins Turbodiesel) with one trailer or type versus another given decent trailer aero qualities.

1) I've pulled the U-Haul 12x6x6 trailer twice over the same 700-mile roundtrip and seen 18-mpg with the combined rig just under 13k in weight.

And,

2) In the same climate & terrain (even some of the same road) pulled my 35' travel trailer and averaged 15-mpg. Combined weight is 17-18k. The rig is 63' OAL.

Solo, I average 24-mpg, and see 26/7 on occasion. This is simply setting cruise st about 1725-rpm or 58/9-mph. Same as when towing. (Truck weighs 7,940-lbs currently).

CTDs are fairly impervious to weight gains up to about 1k. Nothing at all like the penalty with gassers.

But it's a truck sure as hell overkill for a 3k trailer. In the oilfield I used a version of this truck to hotshot trailers in excess of 20k.

A one ton nearly always weighs over 6k, and it's expensive to move that mass. (Parts, component repairs, tires, etc).

Long acquaintance with all-aluminum aero trailers tells me there's no real advantage to low weight. A 6k 28' trailer isn't really any harder to move down the highway than a 4.5k 21'.

But the latter is FAR more "livable". Bigger capacities is king for RVs. For staying put and not having to run to town for supplies.

Sure, there's a limit to size vs. efficiency. But there's also a sweet spot:

A 12-13k pound combined vehicle is economical. Dead stock. (Given a turbodiesel drivetrain and motivated operator).

I'd like to recommend two things. To inform your thinking, not de-rail it.

I hate to see folks re-invent the wheel. To that end I first recommend perusal of Streamline & Silver Streak Trailer brands sales brochures from the 1960s. Some can be found on the Toms' Web Page website. There are Facebook pages with which I'm unfamiliar.

These manufacturers had Full time staff taking exquisite time to maximize space utilization. Capacities.

There are beautiful restorations of Airstream trailers available for viewing (the low end trailer of this type) over on Airstream Trailer & Motorhome Owners Community. But those renovations usually have compromises that negatively affect utility. It's very hard to get all of it right.

The space is so small that the penalty for missing the mark is huge.

I strongly favor buying used, and making sensible modifications in an overall sense (the least important RV system is the electrical . . but it's where folks go nuts today on solar electric. $$$ and questionable longevity). By overall I again reference

X people for Y nights without re-supply.

It's really the question to answer.

The truck you wish to have is now the penalty. A 3k aero trailer will not sufficiently reduce fuel burn substantially enough (over the above direction of renovation) to enable travelling greater distances on the same budget. M

Second,

Let me put this another way: rhetorically, when will circumstances "force" you from the RV to ordinary housing? Death is obvious, so is generalized paralysis (and other).

Weather (past mechanical breakdown and fire) is the most commonly cited reason. (Hail, tornadoes, extended sub-freezing, etc).

Temporary evacuation, extended, or permanent.

RV'ers (fulltimers, in that parlance) always need "an exit plan". Selling a CTD is usually easy. Selling an RV one will wait six months or more (and not at all in winter; it's an emotional purchase).

The farther advantage, therefore, of renovation versus new construction is ease of sale. There's always a buyer for the famous marques. Especially one where all systems are functional, leaks addressed, etc. Its an advantage that it's been out on the road.

As a corollary, the community (loosely) of fellow owners is not to be taken lightly. Not for practical reasons (repairs) or social.

I say all this (and more detail would append) as the choice of a CTD will likely cap MPG in the low twenties. That's as high as I'd go in guessing. It'd be impressive, but it's not 30+ as can be done with a different TV and trailer.

What I'm suggesting (context, not dissuasion) is that a quite comfortable and satisfactory road is already blazed thru the woods. You'd do it on less fuel, but all other concerns are basic to what's needed.

1) A one ton truck is a limiting factor
2) New construction usually takes years, and is fraught by compromise
3) Community of others not to be lightly dismissed
4) Eventual sale is part of ownership cost (which influences operational cost)

Fuel is usually less than 1/2 of daily expenditure. All other owner and operator costs will nearly equal it. THEN the cost of provisions and ground rent will exceed fuel on a per night basis.

A tool defines its use.

A CTD both gives and takes.

"We" usually recommend a buyer get the trailer first. It will determine the TV. By doing it the other way, the TT needs to be mated to the TV for full advantage.

Last, a crank-up "Alaskan" topper would be more useful than a flatbed and occasional camper. Flatbeds get terrible MPG. If I just had to homebuild, this is where I could most beneficially get utility and aero all in one. Solo or towing.

.