Surprising Fuel Savings at 55 mph

[Lumatic]

Originally Posted by ROBERT CROSS

Yep.

Bob

I've wondered the same about camper shells. From what I have read they either don't make any difference or cause lower mpgs.

[ROBERT CROSS]

Originally Posted by Lumatic

I've wondered the same about camper shells. From what I have read they either don't make any difference or cause lower mpgs.

I can see where a properly designed cap could actually improve mpg.


Bob

[Bill M.]

I think a flat cover on a open pickup bed actually increases fuel milage, both while towing and running empty. I could see a very heavy, large cap on a light truck maybe adding enough weight to lower milage.

[Phoenix]

In the past couple of years, skirts have been installed underneath some semi-trailers to cut air turbulence under the box and between the tractor wheels and rear trailer axles. I wonder if some kind of skirt between the pickup bed and the front of the Airstream would improve fuel economy...

[slowmover]

Aero treatment of each vehicle is the simple optimum. The "Aerolid" shown above hasn't reached production, but takes that gasser 1/2T to 25-mpg. A half-tonneau cover is the next best as the open area just behind the cab induces a vortex across the bed that "equalizes" pressure on both sides of the tailgate. A full tonneau cover is about the same or bit better than a close-fitting, cab height bed topper. Any of these are better than an open bed.

The gap between TV & TT is a major hurdle. There are some indications that roof deflectors may work, but we lack the genuine evidence thereof (non-anecdotal A-B-B-A testing, etc). This is where Andy's recommendation of an airspeed indicator will show problems (reversing winds). One can feel them as they hit this gap. Air is then flowing not only longitudinally, but latitudinally. Hairy stuff considering the wind speeds encountered.

As in my earliest post, the mechanical baseline (pressures, align, drag) are the places to focus attention on past travel speed of below 60-mph. Reduction of acceleration & braking events, plus fewer steering wheel inputs are all good for safety, economy, and stress reduction.

Final drive ratio gearing would be the last thing on the list. For a given TV-TT combination that isn't altered much in weight from trip to trip (all trips: to Alaska or to the local lake) could be dialled in just so for all conditions encountered. This assumes an overpowered TV (as most are).

And, Bob, cover the bow opening to your boat and affix to Sub roof (as well as cover the rest). You'd see an FE change.

.

[Lumatic]

Originally Posted by Phoenix

In the past couple of years, skirts have been installed underneath some semi-trailers to cut air turbulence under the box and between the tractor wheels and rear trailer axles. I wonder if some kind of skirt between the pickup bed and the front of the Airstream would improve fuel economy...

I have wondered the same thing.

Besides underneath, some semis now have a deflector on the back of the trailer.

I suspect you would have to put on the same kind of mileage the semis do to see a justifiable savings. I have not heard of anyone who has tried it on an RV level

We need an aeronautical engineer to chime in here.

[slowmover]

Originally Posted by Lumatic

I have wondered the same thing.

Besides underneath, some semis now have a deflector on the back of the trailer.

I suspect you would have to put on the same kind of mileage the semis due to see a justifiable savings. I have not heard of anyone who has tried it on an RV level

We need an aeronautical engineer to chime in here.

There has been some work done over on Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com where the knowledgeable reside (Phil Knox).

Best TT would be "bullet nose" with a "boat tail" (likely truncated).



Section these in half to give a barely rounded underside and completely enclose wheels.
.

[Lumatic]

[slowmover]

But the edges need to be radiused. Not optional. Those square edges kill the other advantages. Radius should be from 12-degrees to around 22.

The roof sloping up, and then down, is also crucial. (No more flat roof)

[nickcrowhurst]

Here in the UK the manufacturer's published highway fuel consumption figures are based on a steady 56 mph in accordance with law. Not surprisingly, vehicle designers will optimise vehicle economy around that speed so as to impress buyers with advertised fuel mileage figures. Certainly this is the case with my UK 1990 Land Rover 200tdi Discovery. At around 56mph I can average over 30 mpg, and the engine is remarkably smooth at that speed.
My superficial research indicates that in the USA the highway mileage is calculated at an average of 48 mph, and never exceeding 60 mph throughout the test:
Detailed Test Information
When I'm in the USA, my Dodge Ram Cummins 3/4 ton achieves 22mpg solo when driven at a steady 55 mph, and again the engine seems very smooth at those revs.
It would be interesting (to me, at least!) to know how these legal standards affect the design of, for example, camshaft profiles and fuel injection patterns.
Wind resistance is king, but perhaps this is another influence.
Nick.

[slowmover]

I also have a CTD. Max pulling power, smoothly, is within the 56-66 mph range on an all-stock 3/4T truck. I think the OEMs expect that these heavier pickups will actually do work instead of acting solely as commuters (1/2T pickups) where gearing/tuning "may" slightly favor higher speeds.

[Lumatic]

or this

[Aage]

Gotta love those things. I would very much like to see one in the flesh, where I could actually get into it, and see the future through Buckminster Fuller's eyes.

I don't think it would make much of a tow vehicle though, what with the rear steering it used.

But wow, it WOULD make a great toad!

http://en.wikipedia.org/wiki/Dymaxion_car

[SteveH]

Originally Posted by Lumatic

Wow! Look at that Reese Dual Cam hanging on the tongue of that thing. That tells you how old THAT technology is.

[Lumatic]

Originally Posted by Aage

Gotta love those things. I would very much like to see one in the flesh, where I could actually get into it, and see the future through Buckminster Fuller's eyes.

I don't think it would make much of a tow vehicle though, what with the rear steering it used.

But wow, it WOULD make a great toad!

Dymaxion car - Wikipedia, the free encyclopedia

This moderator is da bomb. I hoped to catch somebody before he busted me

[overlander64]

Originally Posted by SteveH

Wow! Look at that Reese Dual Cam hanging on the tongue of that thing. That tells you how old THAT technology is.

The photo is of Dr. and Mrs. Norman Holman and was taken in either the late 1960s or early 1970s. Dr. Holman built the "Liner" in 1936 utilizing plans published by Wally Byam and sold through either Mechanixs Illustrated or Popular Mechanics. The trailer and its owners were regular participants at WBCCI International Rallys up through the death of Dr. Norman Holman, Jr. near the conclusion of the International Rally near Sedalia, MO in 2012. Dr. Norman Holman, Sr., and later, his son Dr. Norman Holman, Jr. made regular presentations at International Rallys regarding the building and subsequent modifications to the trailer over the years. Dr. Norman Holman, Sr. was a gentleman of innovation and applied many innovations to his trailer throughout the years, and I suspect he was among the first adopters of the Reese Dual Cam Sway Control system when it became available. I count myself as being very fortunate in having the opportunity to hear Dr. Norman Holman, Sr.'s discussion about his "Liner" more than once as well as Dr. Homan, Jr.'s presentation "My Father's Trailer" on more than one occassion. The trailer can be easily recognized today by its WBCCI membership number -- 1936.

Kevin

[Phoenix]

Regarding towed shapes, I had forgotten about when we towed boats. In the past, we owned the following:

* 16-foot, open bow, (fish & ski) tri-hull with 70 hp outboard that weighed about 1500 pounds (including single axle trailer).

* 19-foot, cuddy cabin (closed bow), deep-V with 120 hp inboard/outboard that weighed about 3000 pounds (including single axle trailer).

* 27-foot, cabin cruiser, deep-V with 360 hp inboard/outboard that weighs about 9,500 pounds (including triple axle trailer). (We still own this boat.)

The first two boats had practically no wind resistance over and above that of the tow vehicle. I guess since the hulls were designed to minimize drag in water, they also reduced wind resistance at highway speeds. I don't recall them increasing fuel consumption much, if any. And, I hardly noticed any additional drag/weight, except for the 19-foot boat on long upgrades.

The 27-foot boat probably has low wind resistance, too, since it is not seriously affected by passing semi's and crosswinds. However, the weight of the boat and motor, along with the triple axle trailer (which weighs 2,000 pounds without the boat) seriously affect fuel economy, even on the flats.

Maybe, a skirt is unnecessary; if we could put a long, pointed bow on the Airstream, and literally make it look like a "land yacht".

[ROBERTSUNRUS]

Hi, I find it very interesting that many people on this forum [some on this thread] talk about, "If you can afford an Airstream" you can buy this hitch, change to this type of brakes, buy this type of brake controller, buy these tires and wheels, buy this type tow vehicle Etc Etc Etc. Like money is water and now they want to squeeze every mile per gallon from their fuel. Hey, if you can afford an Airstream, then you can afford to buy the fuel to tow it with too; And drive at a comfortable speed that is usually with the flow of traffic. For me to get better gas mileage, it will have to wait until I buy a newer, more efficient tow vehicle. Until then I get between 10 to 11.5 miles per gallon with the conditions that the traffic and weather give me.

I refuse to drive at 47.153624 miles per hour to pinch a few more miles from a gallon of gas.

[Kosm1o]

Ha Ha. I was thinking that too. I get about 12 on average with my 2011 1/2 ton Chevy. But I drive closer to 65. So, I can go 10 miles farther per hour. In a 10 hour trip that keeps me from driving in the dark because I refuse to get up early just to get somewhere earlier.
Nonetheless, its good to know that 55 is a speed for much improved fuel economy. I once got caught low on fuel somewhere between Casper WY and Custer SD. I probably would have run out of gas but for driving slower.

[switz]

I have had over a dozen experiences pulling U-Haul equipment such as car haulers and small trailers. Lack of preventative maintenance has contributed to rental units providing challenging experiences. The brakes were operational on one side of a car hauler, thus we experienced a jack knife going down a hill when we started using the brakes to slow speed creep [I called this a laundry generating experience]. I have had several tire failures (usually the GYM brand) and once a unit with a broken spring. U-Hauls suggested 55 mph was probably a good thing as the incidents would have been more challenging at higher speeds.

Our first RV trailer is our Airstream. I find that driving at 55 mph when towing allows for more reaction time when in traffic and allows for time to react the the road alligators we have in Arizona. In my experiences driving 55, I have seen new items of interest beside the highways in terms of scenery and physical structures that were missed when concentrating on the road ahead at 75. I can drive more relaxed, except for construction zones with concrete barriers can still generate a high level of concentration to maintain center in my lane.

On the interstates, many of the semi trucks are not running at the higher posted speeds for several reasons. Of course there is increased fuel economy, but there is less wear and tear on the brakes, transmission and engine. The faster one goes, the more horsepower that is required to overcome the air resistance, ground friction etc and that generates more stress in the internal components of the engine.

There are some highways where there is also a posted minimum speed and it is usually 45 mph.

My tire conversion from 15" GYM to 15" Michelin will allow me the option for higher speeds without fear of tire failure.

YMMV