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Old 10-16-2009, 12:59 PM   #1 (permalink)
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HYPERMILING & TOWING: A Misconception

I found this under hypermiling tips. I believe it to be incorrect in several ways.

Safety is well-enough represented, but what of utility? What can my vehicle do, and how do I minimize costs without minimizing safety? Utility is a vital part of "economy".

106) Avoid towing
Trailer towing delivers the triple whammy of increased weight, higher aerodynamic drag, and a third (or fourth) set of tires for more rolling resistance.

Carry loads in the vehicle if possible.

If not, minimize towing speeds and adjust your technique to account for the extra momentum the trailer and its load will add.


To reverse the order, point two Carry loads in the vehicle if possible goes against all advice and experience I have seen in re long-term economy (longer drivetrain life due to decreased engine load).

1,000-lbs loaded onto a trailer is much easier for a vehicle to deal with than the same load placed in the tow vehicle. A pair of draft animals can transport a heckuva lot more with a wagon than some magickly balanced load distributed on their backs. Same with soldiers dividing up a load onto bicycles or a cart versus humping same.

Point one is a bit ridiculous. Of course one will use more fuel, but, following manufacturer guidelines, it is well within the practical use parameters of the vehicle. Rather like saying, never carry any passengers. I buy a vehicle to do work, this is obvious. Could be your fragile little eco cars aren't worth much (air conditioned go karts), but most of us need practicality in our single do-it-all vehicle. And that assumes a bit of robustness.

No, the real question is properly matching the cargo trailer (CT) and tow vehicle (TV) and being certain the hitch rigging is dead-certain.

A well-balanced rig -- TV & CT -- according to actual weight on the axles derived from a scale (CAT Scale Search)

where the load on the steering axle has not decreased; or, has increased according to formula is the basic rule. Trailer tongue weight (TW) needs to be 10-15% of the trailer weight (again, generally; depends on trailer type); and TW needs to show up on both TV axles AND CT axles when all is said and done.

There is more to it than this -- the devil is in the details -- but this is the basic way of perceiving this problem.

Let's assume an enclosed cargo trailer, tandem-axle. Dry weight of 2,500-lbs with a 2,500-lb load capacity for a CT gross weight rating (GVWR) of 5,100-lbs.

The TV is a larger car/minivan or pickup.

An ideal TW would be (13%) 650-lbs. Now, let's assume that our TV can deal with this load with proper hitch rigging and we have perfected same with trial & error attempts. In other words, the two vehicles weights & capacities are not an impediment to moving the load SAFELY.

What is the mpg problem?

According to a White Paper published by both Cummins and Kenworth -- for the big truck industry -- the single impediment to mpg is

Below 50 mph: rolling resistance

Above 50 mph: aerodynamic resistance

So, my enclosed CT should have, at a minimum, appropriate load-rated tires designed for least rolling resistance on the road; a "highway tread".

And here is what is missed by many:

The axles should be aligned, professionally.
The brakes should not drag or bind.
The suspension should have shock absorbers.
One wants a state-of-the-art brake controller in the TV.
One wants a hitch that prevents -- not just damps -- trailer sway. (All trailers sway, it is only a question of how much).

The trailer, empty, should roll straight. Loaded, same (load must be balanced side-to-side, not just front-rear.

Assuming that the TV has been checked in the same way (drivetrain reliability questions concerning heat management, brakes, etc) then

the only thing left is aerodynamics.

The White Paper[s] go on to explore aero aids. The biggest "problem" is airflow between the TV and CT. A gap wider than 30-inches is the airflow killer for the hitch rigging,

and,

I would state, the one least likely to be remedied in other than a purpose-built vehicle. (My truck and [bumper pull] travel trailer saw a gap of just over five feet, as an example).

What remains is CT height, and width.

A width the same or less than the TV is ideal. (And easier to deal with in traffic for sightlines and general maneuvers).

Height is the real mpg killer once we have adjusted for all other conditions as found.

So, if my 5,000-lb trailer is the same width or less as the TV, and is no taller

my fuel economy is not so adversely affected. Length, weight, etc, are not so nearly important. Give me a longer, but lower, trailer.

Second is an overall aerodynamic shape. RV'ers have a hard time understanding this one, but I know this crowd won't.

No square corners, and enclosed undercarriage are great.

But pale next to height.

I'd rather have the trailer above: optimized rolling resistance and best aero compromises present when I'm contemplating a load for a trailer.

We all have need, on occasion, where a trailer is the best choice. We can all imagine a scenario -- weather, earthquake, fire, war, etc -- where time and our choices are limited AND our vehicle is the only way to do it.

Economy is best with optimizing details in that situation. Mainly, a road speed around 45-50 mph. And spare fuel aboard.

In the steady-state world, 58-60 mph on the Interstate (roughly, 10 under).

For "peacetime" then some study, and some investment into the best tow vehicle and matching trailer -- cargo, construction, travel, etc -- pays dividends.

The third point, [above] is to adjust driving. Of course. One will need more power at many points: acceleration, braking, etc. It isn't hard with practice

when one understands that he is the slowest, worst-handling vehicle on the road.

The trailer I used as an example is the largest enclosed trailer offered by U_Haul at under 6' tall and 12' long. I loaded it and my truck, and, with an estimated gross weight of between 12 and 13,000-lbs I saw a solid 19 mpg to move over 3,000-lbs of goods on a 300 mile trip. I could have loaded both vehicles to a higher level had I another sort of goods and likely returned the same or similar miles.

My 300-mile fuel cost was (at $2.6/gl) $41. Or, 13.5 cpm (cents-per-mile).

The industry of moving things (trucking) looks at that: all expenses divided into miles to understand cost.

Previous to this I was averaging 15 mpg with a 7,500# 34' travel trailer at a higher road speed. I could likely have broken 16 mpg had I dropped some rpms/speed. This is consistent with some others I know of with similar trucks and trailers; or, simply: a diesel pickup and a lighter weight aero trailer; where the scale tickets showed a gross of nearly 16,000-lbs with a 9' high trailer.

Mpg, solo (7,360#; at the higher speed) is 22+ (versus 15 towing the TT; 16,000#).

Mpg, solo (at the lower speed) is 24+ (versus 19 towing the CT; 13,000#).

Diesel is the magic when it comes to towing. High compression just flattens out the hills. A manual transmission means all miles are within the "sweet spot" for the engine: accelerating, cruising, etc.

A gasoline powered 3/4T truck of the same make & vintage would average, (per others experience) around 7-9 mpg towing, and 15-17 mpg solo. Even if higher, you can see the "diesel benefit" (exclusive of initial cost [offset by greater capacity and longer life; i.e., buy a used truck]).

And so forth.

If you understand your cost-per-mile (all costs, including depreciation, finance [foregone investment], taxes, insurance, fuel, repairs, maintenance, tires, etc) then the "cost" of towing is one where vehicle life is maximized, safety is never compromised and driver condition is comfortably alert over a long day.


Last edited by slowmover; 10-16-2009 at 01:07 PM..
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Old 10-16-2009, 03:49 PM   #2 (permalink)
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Quote:
Originally Posted by slowmover View Post
1,000-lbs loaded onto a trailer is much easier for a vehicle to deal with than the same load placed in the tow vehicle.
Why? If you have 1000 lbs in the vehicle, you have to move an extra 1000 pounds. If you have it in a trailer, you have to move 1000 pounds plus the weight of the trailer. Plus you have extra air resistance, tire & bearing friction, etc.

Quote:
A pair of draft animals can transport a heckuva lot more with a wagon than some magickly balanced load distributed on their backs.
That may be 'cause you have problems finding draft animals that come with wheels :-)
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Old 10-16-2009, 04:31 PM   #3 (permalink)
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...provided you can safely load the stuff internally in the first place. A thousand pounds is generally a pickup load, depending on bulk, and I would not recommend loading it *inside* the average economy car at all, though the same car can probably safely pull way more than that in a trailer.
While it's a great thing, trying to drive as efficiently as possible, I'll still keep safety higher on the list.

By the way, trailers don't handle badly at all when properly loaded. The person who believes otherwise could probably use some instruction in that regard.
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Old 10-16-2009, 06:17 PM   #4 (permalink)
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Quote:
Originally Posted by jamesqf View Post
Why? If you have 1000 lbs in the vehicle, you have to move an extra 1000 pounds. If you have it in a trailer, you have to move 1000 pounds plus the weight of the trailer. Plus you have extra air resistance, tire & bearing friction, etc
This is a matter of forgetting acceleration, deceleration and any handling dynamics.

A static load is easy. Driving a vehicle where the load is nearly the capacity rated is not. A trailer removes that burden.

The loaded tow vehicle is straining more than you realize (and station wagons through the 1990's could carry up to 1,200-lbs; minivans are impressive, too); the trailer places that load onto a platform designed only to carry a load, not passengers, etc. Rolling resistance is lower than many realize. A child can push around a balanced trailer when a slimp wheel is mounted.

And, with a top speed of around 58-60 mph, wind resistance is minimal where trailer height and width are kept down.

Think of a Tahoe with Dad, Mom and the kids. The cargo area is maxed out. There's a pod on the roof. And a hitch receiver mount cargo carrier with a box. Every aspect of utility and economy would be better with a trailer (and, obviously, a smaller vehicle could have been used in the first place).

A well-sorted rig can also stop faster -- in a shorter distance -- than the solo vehicle can alone.

Trailers have their place, but don't assume you've ever

A) seen correct hitch rigging; and,
B) seen a well-matched TV and trailer.

You'd change this "obvious" opinion in a hurry.

The numbers work well in favor of a trailer in many circumstances.

Loading, hitching, etc, is a different thread topic.
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Old 10-16-2009, 07:24 PM   #5 (permalink)
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I like trailers very much, but only because I rarely need to use them. It allows my vehicle to stay relatively tiny (and efficient) most of the time without the added expense/maintenance of a large vehicle that would be underutilized.

For the few times that I need to move a washer/dryer, or a couple motorcycles, or landscaping, it is awesome, and easy to load.

The handling/safety question is irrelevant IMHO, all vehicles are different and it is the drivers job to operate it safely in any configuration. We can't all drive Porsches.
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Old 10-16-2009, 08:28 PM   #6 (permalink)
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I once bought a dryer, and it just fit into the hatch for transport. I was better off with it inside than in a trailer. I also had to move an empty 18 cube feet rooftop cargo box once. I was able to fit it in the back seat of my sedan instead of putting it up on a roof rack. I think that's the nature of the discussed fuel economy tip.
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Old 10-16-2009, 08:44 PM   #7 (permalink)
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I moved a washer, dryer, and 2 stoves inside my van. I guess they'd have been better off on a trailer behind my van?

Inside my Caravan, I can move 7 people (which already maxes the weight limit, but not the cargo space, not nearly), and still have room for a couple bikes or camping equipment inside the van, if one were inclined to "roughing it".
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Old 10-16-2009, 09:59 PM   #8 (permalink)
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Quote:
I moved a washer, dryer, and 2 stoves inside my van. I guess they'd have been better off on a trailer behind my van?
If the van was able to do it well, and without any handling difficulties, not at all.
As far as my post was concerned, my concern was mostly the ability of the vehicle to safely carry the weight, and why a trailer is a safer bet if not. Any assumptions otherwise belong to the originator of that assumption.
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Old 10-16-2009, 10:05 PM   #9 (permalink)
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I think that's the nature of the discussed fuel economy tip.

If read one way, yes, that could be seen. It might also lead one to think that having a shipper handle the goods is the better decision. In fact it may always be, but it is considerably more expensive, even prohibitive.

As to moving an appliance across town, yes, it fit the hatchback; by the above, would one want to move across state thusly? Because one can, does that mean one should?


The handling/safety question is irrelevant IMHO,

Safety is never irrelevant. One has -- always -- but a single chance to avoid disaster. Planning otherwise, as in, "I'm exempt from physical laws", or, "I've never had a problem taking shortcuts in hitch rigging, are ways of inviting $$$ problems as well as legal liability.

In trailer towing the tail wags the dog. A lightweight trailer, improperly loaded and/or hitched, can flip even a heavy tow vehicle. Polar-moment-of-inertia.

Whether a trailer is used regularly or irregularly one still can make the journey more safely as well as at a reduced cost by attending to details. Ecomod as a concept is one that works here.

I like trailers very much, but only because I rarely need to use them. It allows my vehicle to stay relatively tiny (and efficient) most of the time without the added expense/maintenance of a large vehicle that would be underutilized.

Bingo! But what of when the trip is cross-country, of a weeks duration, and thousands of pounding miles on goods, tow vehicle and driver? Attending to basics -- and to fine-tuning -- pays upfront, and pays long-term.
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Old 10-16-2009, 10:28 PM   #10 (permalink)
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This is like a DAH moment.

If the load is within the vehicle's rated capacity, then load 'er up and go with it. The hypermiling tip is correct in saying the trailer is extra weight and etc. BECAUSE IT IS.

Overloading a vehicle is no different then overloading a TRAILER so don't do that either.

Who was talking about overloading anyway? Oh yes, that's right, nobody.

Sometimes the trailer is the best solution and sometimes it ain't. Wanna go through every possible load/vehicle/trip combo? My A.D.D. won't allow me to follow along.


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