HYPERMILING & TOWING: A Misconception

[aerohead]

Originally Posted by jamesqf

I did read it. You claim that it's always better to tow something than to carry it inside, which is nonsense, expecially when it relates to performance.

Sure, there are times when towing's the better choice. I'm not, for instance, even going to try to convince my horse that she ought to ride in a pickup bed :-) And it's better to tow the occasional load - those sheets of plywood, for instance - behind a small car, than to always drive a vehicle big enough to carry them. But you're paying an additional penalty, the extra weight & drag of the trailer, in order to reduce the cost of driving all those times when you're not pulling the trailer.

The only thing I can bring to the table is my experience with the CRX.
That car has a 400-pound max. load limit.It is not rated at all for towing.
I fabricated a 1-1/8" ball hitch for it and pulled a utility trailer with only an upper body shell from the Dallas/Ft.Worth area to Los Angeles,California and back,running with a 1,300-lb load on the return leg.
MPG dropped from 52,to 50 mpg @ 55-mph.
By putting the load in the trailer I was able to run 900-lbs overweight with only a 3.84% drop in fuel economy.Of course,this was a majority of steady-state highway driving.
This an instance when the trailer offered an alternative unattainable with the tow vehicle.

[slowmover]

Most vehicles can tow a trailer. Actually, most all, is a better way to put it. While I got off on the wrong conceptual foot in this thread, there are ways to analyse what a vehicle is capable of (axle ratings, tire ratings) that are of use. Vehicle manufacturer "ratings" do not have the force of law in any respect, they are what those "individuals" are comfortable recommending (thus the conundrum of the exact same vehicle sold overseas having the ability to tow two or three times as much).

It's reasonable to expect a 30-40% drop in mpg for a conventional, fairly large trailer. Less so the more aero is the rig along with fewer stops or hilly terrain.

An overloaded single vehicle -- we've all seen it -- where the passenger compartment and roof are jammed, crammed and tall, is the poor choice where some trailers can provide a better way to move the same load. And as cheaply in fuel, sometimes better (due to aero, COG, and fewer steering inputs).

I've done it both ways. The cost of a trailer rental was not offset by mpg that was better with the trailer, but the improved vehicle handling -- in a relative sense -- offset that to my satisfaction. It's distinctly easier for a tow vehicle to pull a load that would strain it if carried aboard.

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[aerohead]

I'm really a newcomer with respect to trailers.I've enjoyed the limited exposure that I've had so far and now keep a 3rd eye open with regards to all things trailers,as so many folks I know are now dealing with them.
Most surprising of all is the limited peer-reviewed documentation on performance prediction capabilities.
With Scan-Gauge capability now,members ought to be able to construct a complete performance profile of their rig,simply by documenting observed mpg under the varied driving environments encountered during travels.
I'm having to deal with eleven simultaneous unknowns while attempting to reduce the data from my Sept/Oct trip with the Viking trailer.What a PITA!

[slowmover]

Originally Posted by aerohead

I'm really a newcomer with respect to trailers.I've enjoyed the limited exposure that I've had so far and now keep a 3rd eye open with regards to all things trailers,as so many folks I know are now dealing with them.
Most surprising of all is the limited peer-reviewed documentation on performance prediction capabilities.
With Scan-Gauge capability now,members ought to be able to construct a complete performance profile of their rig,simply by documenting observed mpg under the varied driving environments encountered during travels.
I'm having to deal with eleven simultaneous unknowns while attempting to reduce the data from my Sept/Oct trip with the Viking trailer.What a PITA!

With Scan-Gauge capability now,members ought to be able to construct a complete performance profile of their rig,simply by documenting observed mpg under the varied driving environments encountered during travels.


Predictability is everything. The problem is always: new roads, with new loads, and wacky weather/wacky traffic (outside of perceived norms).

TX_dj description of Ultra-Gauge capabilities has my attention for what I've been missing in this regard (for diesel trucks).

Outside of critical mechanical issues, the rule of thumb for a cargo trailer ought to be that the trailer is no taller or wider than the vehicle towing it. Length is where the additional cargo space can be found. Aero trumps weight in all considerations for highway use.

The first divider is occasional use versus regular use. The formers impact on annual fuel burn is minimal. The second -- as percentage of miles per year, and anticipated years of use -- is where homework needs be done. In this case, the trailer trumps the tow vehicle for order of importance. Spec trailer first, then spec & purchase tow vehicle.

As example recently came across a thread on an RV forum where the tow vehicle was a HONDA RAV-4 and the travel trailer a tiny 16' fiberglass egg CASITA. The owner reported mpg figures consistent with my 3/4-T truck solo & towing a 34' travel trailer. A better chosen TV in that instance would have seen much better fuel mileage. (His overall vehicle costs were actually higher than mine if purchased new).

I'm having to deal with eleven simultaneous unknowns while attempting to reduce the data from my Sept/Oct trip with the Viking trailer.What a PITA!

Never seen anything like it for information-collection (that thread).

Logging every trip will obviously produce a set of reliable datum. But once one changes just terrain (or climatic conditions) it all changes again. Electronic engine controls have made today's vehicles much more consistent in solo use with regard to changes in terrain, climate, and vehicle spec, but towing opens the deficiencies right back up again. A spring-like day on US-287 near Ft. Worth is one thing . . a wintry day on US-287 near Thermopolis is quite another. What is a bit of a hurt while solo is noticeable, but while towing it may mean not making ones destination on time or in budget. (This is where strict trip-planning pays off).

The more closely one can define need and use over time and miles, the better the ownership and operating costs.

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[larrybuck]

Some good information here, but some beating the dead horse as well.

I would love to see some of your personal stats, if you would share them, about what your base empty PU mpg. empty is for long freeway cruise, with added, lets say a bumper style pull 28-32ish foot travel trailer at the same cruising situation, and your tricks to keep those 2 figures closer to together than apart.

I know different trucks are different, but in theory, what would be a good rear end diff. ratio for that 50mph long living. I have a '85 Suburban w 6.2, w the 700R 4 spd. auto. It has 3,70's, or 3.73 ish. Though a K model, it has manual hubs, and only 31's for tires so it sits almost 2wl drive low.
Alone, mid 20's-30mpg. is still possible.

Would BF Goodrich Mud/All Terrain tires change my mpg. like falling off a cliff, or not; up to 33's much difference in all at 50mph or less cruise life?

Would greatly appreciate some input.

I liked the sharing of the CRX towing example as a clue to seeing real life results.
That is the pertient info example that would help, though I do cringe at the thought of MY CRX having to tow anything.

For us mpg. people, and the general future of smaller, lighter cars in the future, do any of you think that the 1 tired cargo trailer might make a comeback???
I remember as a kid watching my Dad pull one on one of our vacations.

Obviously, design is SO important here, generally the motorcycle/bicycle people probably have much more proper application experience here.

Your thoughts, please!!
Thanks!

[slowmover]

I would love to see some of your personal stats, if you would share them, about what your base empty PU mpg. empty is for long freeway cruise, with added, lets say a bumper style pull 28-32ish foot travel trailer at the same cruising situation, and your tricks to keep those 2 figures closer to together than apart.


Oh, boy, detail time. Below is an assumption of a pickup truck and a travel trailer (for the most part) where higher than average miles is expected (5k-plus annually). As always, vehicle specification is paramount. Nothing will overcome bad choices. Truck aero and trailer aero are separate issues. No wing or other devices on the truck will "help" the trailer as the gap between vehicles is too high (unless one lives in Sanger, Texas). FE is small changes adding up to percentage increases. Maximizing mechanical leverage details makes for a better handling, better braking, better tracking rig. Less wasted energy in forward motion.

Rolling resistance concerns are of a higher order than when solo, thus this set of posts about hitch rigging.

This is the "how to" (short version).

My numbers:

For solo, at 58-mph, 1,725-rpm cruise across Gulf Coast Texas, on 700-mile roundtrips (including traversing Houston twice each time) I never fell below 24-mpg, loaded, empty, winter or summer, rain, dark, traffic, etc. Highs of 27-mpg numerous times. Did this trip over two dozen times. Never a straight tail or head wind. And winds always shifted at the trip mid-point.

With a 34' TT (6860-lbs empty, 7,500-lbs loaded for full-timing; .94 of 8k GVWR; under 16k combined), saw from 13-mpg on hilly two lane backroads with lots of small towns, and then open flats. On the same highways as in the solo, above, saw 15+ mpg. All of this was at 63-mph, my previous cruising speed. Had I slowed to the present 58-mph, I'd have broken 16-mpg. These miles were in Texas.

The above figures are consistent with other owners of the same brand and near MY truck, plus very similar trailers (all aluminum, aero, low COG, relatively light weight, etc), some of whom do better than me. Non-Cummins powered GM pickups from the early 2000's do the same. My comparisons range across mainly RV'ers, but some commercial drivers in there too; all of them in the Southern or South Central US to keep variations for climate and terrain to a minimum.

The spread is at about 31% for this trailer type from solo to towing with a CTD or Duramax. Ford is less desirable (not just FE). The gasser range is closer to 40% when using TRAILER LIFE articles on rig performance be it 1971 or 2011.

With U-Haul's biggest enclosed trailer (12x6x6) and at about 13k GCW, saw 18/19-mpg empty and loaded on the above roundtrip routing. Saved more money by renting in one city instead of point-to-point dropoff. The other savings was in using a MASTERLOCK 500/5000 Adjustable Hitch



in order to, using a level, tilt the trailer nose just barely forward of perfectly level. I also loaded and sometimes re-loaded the trailer to get the lowest COG and have it ideally placed versus the trailer axle.

U-Haul does not have a good record in taking care of it's equipment, not at the level I think they should. So part of my inspection is to see that the surge brake fluid looks new (and have them change it if not); also to get that device hooked up appropriately (instructions online); and I also take along a torque wrench to apply correct value to lug nuts; and I want to see perfect tire inflation. I also use a flashlight to inspect the underside, not just topside plus treadwear. I also get "underneath" the coupler and clean it out, looking for cracks and galling. The coupler must not be loose (beyond normal). I use wheel bearing grease or whatever is handy to grease the ball and the coupler underside.

(Once hitched, that ball is a critical steering component. In big trucks, the fifth wheel -- as a predictor -- is, if dry, the number one cause of big truck loss-of-control accidents. Not rain, not other traffic or driver error, but a dry hitch. The same, I believe, works for small trailers as well. We want no resistance to returning to center for the trailer).

In their favor, I would love to have a trailer as well designed and built as this U-Haul trailer.

On a trailer I own Step One past purchase is to pull brakes and service wheel bearings, even if brand-new. (I am looking at "treated" wheel bearings by MICROBLUE RACING for the next trailer. Might be worth a full 1-mpg on big truck trailers). Same for axle alignment and wheel balance; the assumption is that it is off. Perfection is just acceptable for these.

Step Two is either new shock absorbers, or to add them on a conventional leaf-sprung trailer (torsion axle [independent suspension] is much superior and not included in the following). I want road irregularities dissipated as heat, not as a trailer that crow hops. A leaf sprung trailer has a high and narrow roll center. It is unstable, already. We want to minimize this.

The goal is lane-centeredness under all conditions. And, as it is difficult to have a perfectly-balanced trailer (in regards ideal tongue weight) either side-to-side, or front-rear, then shock absorbers --like tandem axle equalizers -- help with imbalances even if minor. I've pulled worn shocks off of one axle and found those on the other still good. Weighing a trailer usually reveals what the equalizer has to cope with (and there are upgrades for that component from DEXTER and MOR-Ryde and others). I also add CENTRAMATIC balancers for the finishing touch.

Alignment, wheel balance, shock absorbtion (wheel dampers and the equalizer), and ball grease all add up to a trailer that more easily follows the truck, and is less affected by tripping hazards. You'll have noticed that all too many travel trailers appear to sit two feet off the ground as it is. This high center-of-gravity [COG] is exacerbated by a crude suspension and the tendency to tip (even before wind loads from any direction are added).

Tires are always worthy of discussion in re trailers as the usual ST rating tires are essentially junk, not suitable for extended high speed travel. I'd rather have radial LT tires, for commercial use, of the appropriate rating (and American made wheels with a commensurate or higher rating) for longest service and best performance. One never wants trailer tires to run hot or to hydroplane.

A TPMS is recommended. Trailer tires are notorious for losing air. On the next trailer I plan to use epoxy paint to coat the aluminum wheel interior and to specify that bead sealant be used when the tire is mounted. Trailer tires only have their weight rating at the specified pressure. A day of running them hot, low, is enough to shorten life drastically.

Daily, the trailer needs: A check of all lug nuts for appropriate torque value (I keep a dedicated torque wrench for this), and tire pressure values. One should always check suspension components, and brakes. A hand-held IR device is handy for this. If bearings are too loose or too tight; if brakes are dragging, the IR gun will disclose it immediately. Same for tire temps. TV should have one set of temps, the trailer another. Discrepancies should be addressed ASAP.

I plan to convert the next trailer to disc brakes. I want the best performance with the coolest running when things get tough. And the shortest application time, repeatedly. This is a matter of -- for all vehicle controls -- using the least amount of time/energy to maintain lane-centeredness. Anti-lock is on the immediate horizon for trailers. Disc brakes, alone, mean a shorter stopping distance for a TV/TT combination than the TV alone. One can get there with drums, but adjustment has to be constant to maintain this. Trailer drums are usually out-of-round, even new, so balance, stopping performance, are all compromised. Tolerances in this industry are low, much lower than automotive. Disc brakes on all axles of the rig are just right.

Next post will be about Weight Distribution Hitches.

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[slowmover]

When towing the goal is to remain lane-centered without driver inputs (beyond what was normal for the solo vehicle). Cummins and Kenworth both use the number of steering inputs per X-miles when high as deleterious to fuel mileage.

A weight distributing hitch [WDH] is required even on 1T pickup trucks when trailer tongue weight [TW] exceeds 400-lbs. A trailer with a TW of 400-lbs may weigh as little as 2,500-lbs. The bar is low. The simplest understanding is that a WDH "returns" the Front Axle [FA] to unhitched height/weight values, and that this ensures "normal" steering and braking by so doing. The remainder of the TW is "distributed" over the Rear Axle [RA] and Travel Trailer [TT] axles. When a large force plays against both the TV and TT at slightly different times, the leverage action of the trailer tongue is spread out across all axles of both vehicles effectively dampening "problems".

Now, payload of a truck is, in a manner of speaking, irrelevant to the discussion, overall, as TW is a static measurement of a dynamic problem. That is to say, an 800-lb TW can be 12,000-lbs under the wrong circumstances. The "arm" of the trailer tongue, extending back to the center of the axle is a lever that can upset the TV, drastically. The tail wags the dog. I once watched a portable generator that I know weighs around 1,800-lbs takes a dually pickemup clean off the road. A dry road.

A download of a spreadsheet made by Nickcrowhurst on AIRforums.net showing forces acting upon the rig is here; the thread is a discussion of these factors. One can play with different trailers and tow vehicles given a handful of measurements. This, and the below, are ways of understanding how SAE looks at tow rig dynamics, the forces acting upon the tow vehicle different from solo, and how to re-establish solo handling to the best extent.

The following is chart made up by Ron Gratz a contributor on RV.net, handy for it's brevity and checks. By using a three-pad certified scale (see CAT Scale Locator, online) one can fine-tune a WDH beyond the usual measurements of before/after heights given in Towing Guide instructions by vehicle and hitch manufacturers. Specifics to vehicle ought to be followed.

For a truck, the usual result of proper hitching, today, is that once the FA has returned to the unhitched weight value that the balance of the TW will be distributed from 75-25 to 60-40 on the RA and TT axles respectively. (Copy and print a few):

Weighing #1 -- TT attached and Weight Distribution Activated

Let Front Axle Load be "FA1"

Let Rear Axle Load be "RA1"

Let TT Axles Load be "TT1"

Then, while in same position on scales, take
Weighing #2 -- TT attached and Weight Distribution Not Activated

Let Front Axle Load be "FA2"

Let Rear Axle Load be "RA2"

Let TT Axles Load be "TT2"

Then, drive off scales and drop TT. Return to scales and take
Weighing #3 -- TV only -- TT Not Attached

Let Front Axle Load be "FA3"

Let Rear Axle Load be "RA3"

From the above values, you can calculate:

TV weight = FA3 + RA3

Gross Combined Weight = (FA1 + RA1 + TT1)
- should also be equal to (FA2 + RA2 + TT2) if scale weights are correct

TT Weight = Gross Combined Weight - TV Weight

Tongue Weight = (FA2 + RA2) - (FA3 + RA3), or

Load Transferred to TT Axles
when WD System in Activated = TT1 - TT2


Once these values are established, and some subsequent ones done the same way to account for different loadings, the range of WDH adjustments are known for a given rig. Now is when tire pressures can be zeroed in as highest pressures are not always to the point in braking/handling questions. Same for alignment problems on the TV, slack in the steering gear, etc. In short, any TV shortcomings are magnified and we do not want the actions of the TT to have any farther effect. IOW, if the rigging is ideal, then the diagnosis of handling, braking and FE problems can be isolated and treated.

Now, as to type of WDH; next post.

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[slowmover]

The TV Drive Axle is the Steer Axle of the trailer. The tendency of the trailer to want to move about on its own -- to pass the TV -- is greatly reduced when the proper hitch rigging is installed correctly. Side-to-side motion of the trailer can increase to trailer sway due to all sorts of concerns: trailer design, trailer load, winds, road surface, etc. To keep this at a minimum is the purpose of trailer anti-sway. The better the anti-sway, the less wasted motion in moving forward (less drag, cleaner aero).

The function of a WDH is to spread the 12-15% of TW across the TV, thus keeping handling/braking closer to the solo norm. The addition of anti-sway devices to the WDH keeps the trailer closer to center. Some hitches are designed around a particular concept to achieve this, some have add-ons. The first is a type, a VPP hitch, Virtual Pivot Projection where design linkages simulate a fifth wheel or gooseneck hitch, each of which mounts at or barely ahead of the TV Rear Axle:

GN




Fifth Wheel



(A high mpg example is Kamper Bob's rig: short OAL, lightweight & and decently aero. Another is Skyking's proposed aero conversion of an Avion 5'er TT to take advantage of close vehicle coupling. The trade-off of a 5'er is the loss of the truck bed & enclosure while towing beyond high wind load and COG concerns).

For trailers starting at about 8k, and especially above 12k, a GN or 5'er is pretty well required due to TW requirements.

A VPP Hitch replicates this advantageous arrangement of keeping the pivot point of the rig at the Drive Axle. The farther back from the RA is the pivot point, the potentially worse the handling problems that arise.

The TV Drive Axle is the Steer Axle of the trailer. The tendency of the trailer to want to move about on its own -- to pass the TV -- is greatly reduced. Side-to-side motion of the trailer can increase to trailer sway due to all sorts of concerns: trailer design, trailer load, winds, road surface, etc. To keep this at a minimum is the purpose of trailer anti-sway. The better the anti-sway, the less wasted motion in moving forward (less drag, cleaner aero).

In order of performance, thus preference, the best hitches are those which we might refer to as sway-eliminating:

1] Pullrite This mounts under the truck, and that center bar pivots from a mount point to have the trailer track true in all instances.



2] Pro Pride The improved, new patent Jim Hensley design. Allows a greater range of WD adjustment.



3] Hensley Arrow The original Jim Hensley design patent.



The second tier, again in order of performance, may be called sway-resisting:

4] Reese Strait-Line / Dual Cam




5] E-Qual-Izer (and similar designs by others; preferred for surge brake applications)



And finally, the doorstop known as a "friction device" anti-sway; to be avoided overall as one must disconnect in wet weather, etc, when most needed). This is what maybe 80-90% of folks think of when referring to a WDH (and their "understanding" that a 5'er is more stable) and the "poor performance" of a conventional "bumper pull" travel trailer.



In short, the less movement by the trailer under any circumstance, the less power needed by the TV to maintain headway being lane-centered in all conditions.

Towing is a risky business, and the likelihood of an accident per mile of travel is greater than with a solo vehicle. Thus the best hitch & rigging is neither expensive nor onerous to set up.

Next post: Incidental Concerns.

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