Roof top wind deflector.

[Pete S]

Hi John,

We're in a 2.0L sedan. A couple trips St. Paul, MN to Grand Marais, MN and back got us:

31-32 mpg without trailer.

21-23 mpg with trailer.

So basically we go about 2/3 as far on a gallon or it uses 150% as much fuel with the trailer.

The bearings are clean, greased, and adjusted. The axle isn't all out of line, wheels are straight, tires fairly new and pumped up... I suppose our issue could be as simple as the V-shaped deck on our tongue doesn't let air coming down the front of the trailer (see the VW diagram and you'll see what I'm talking about) escape under the trailer.

I have high hopes for the rooftop air deflector.

[rowerwet]

for VG's on the trailer, I would go for the aft lip on a cargo or the point where the roof starts to curve down, that will keep the air following the skin farther down than normal, also along the side wall aft edges to help the air break up the edges of the trailer.
I wouldn't use VG's on the TV as you don't want to cause more air to run into the front of your trailer. Popular Science did and article on using VG's to improve the airflow on a car with a vertical back window, they worked but the style of VG's never made it on cars, they did make it onto airplanes though. Most car designers don't like the look of little fins, Dragon scales etc. on their nice smooth designs. (the shape of the prius roof, bulged on the sides flat and lower in the middle, does much the same thing)
My own idea is a strong cloth that would hook onto the front of the trunk lid or hatch back and attach to the front of the TD to keep a continuous profile to the TV/TD combination. stretchy hooks would allow the TV to turn along with some slack in the fabric. Not sure if it would work but I would love to try it sometime.

[angib]

Vortex generators were used over the rear window of the Mitsubishi Lancer Evos - the 4WD rally monster that I don't think gets to the US. HEre is Mitsubishi's technical paper on the use of VGs:

http://www.mitsubishi-motors.com/corpor ... 16E_03.pdf

But please note that after optimising them in a wind tunnel (you do have one of those at home, don't you?....), they got a Cd reduction of 0.006 - not much.

[NathanL]

I've big loads with and without a wind deflector. I never noticed a big difference in mileage.

Where it is nice is it cuts down on buffeting. I'm not sure how much a teardrop or a small stand up would benefit from that however.

On a larger flat front trailer it really cuts down on the big buffet when you approach a semi on a 2 lane road at highway speeds.

A lot of stuff comes into play you just can't model. I pull a 38' boat on triple axles pretty often. I get about 1mpg better on average if I take the cover off the front bow than I do when it's on. That's numbers from about 10 years of use on the same tow vehicle.

[Larry C]

If towing a TD with a small pickup, I wonder if a bed cover (tonneau) will help or hinder?

Larry C

[NathanL]

If towing a TD with a small pickup, I wonder if a bed cover (tonneau) will help or hinder?

Larry C

Dunno but you could try it. A lot of people suggest letting the tailgate down....I guess it depends on the truck. When I put a 5th wheel hitch in my truck and used a mesh style open tailgate my mileage went down till I put a regular tailgate back on.

[ParTaxer]

Somewhere I heard that a pickup with a standard tailgate was better than having it open. Something about an air pocket forming in the bed and streaming the air over the bed with less resistance.

[Larry C]

Somewhere I heard that a pickup with a standard tailgate was better than having it open. Something about an air pocket forming in the bed and streaming the air over the bed with less resistance.

I have studied all the pros and cons of tailgate up/down, and using a tonneau or not with a pick-up. It appears there are more opinions than actual science, so I will just try it for myself with just the pick-up.

However, I am wonder what effect the open bed or closed bed has when towing a teardrop? It clearly will change the aerodynamics of the TV/trailer train. Does anyone have any actual experience towing a true teardrop shaped trailer with a pick-up whether an open or closed bed (tonneau cover) makes a MPG difference?

Larry C

[NathanL]

I'll tell you one huge downside to driving a truck with the tailgate still on but in the down position. If you get into heavy rain on a dirty road, or new asphalt on a road, a gravel road etc...all that dirt, asphalt, rocks etc...from the back of the pickup will almost always hit or get on the tailgate in the back.

I did it once on a previous truck I owned and after a few days I needed a new tailgate if I cared about the appearance of my truck.

Think about it, you are putting a painted surface pointed down at the road behind the tires etc...

Just something to think about.

[NathanL]

Somewhere I heard that a pickup with a standard tailgate was better than having it open. Something about an air pocket forming in the bed and streaming the air over the bed with less resistance.

I have studied all the pros and cons of tailgate up/down, and using a tonneau or not with a pick-up. It appears there are more opinions than actual science, so I will just try it for myself with just the pick-up.

However, I am wonder what effect the open bed or closed bed has when towing a teardrop? It clearly will change the aerodynamics of the TV/trailer train. Does anyone have any actual experience towing a true teardrop shaped trailer with a pick-up whether an open or closed bed (tonneau cover) makes a MPG difference?

Larry C

Even if they did I bet there are so many variables such as truck height, teardrop size that you would just have to try it with or without. If you don't already have the cover I would try and figure "best case" to see if it's worth it money wise depending on how often you tow your trailer.

[Pyrofish]

As for the tail gate up/down or the tanneu cover, I think Mythbusters did an episode on that. Just saying

Enjoying the thread. I have a tall CT that I'm wondering if a wing of some kind could help. Maybe mounted in the front stake pockets of my TV bed. It would need to be sharp, as I think the difference in height might be 3' for me

[rowerwet]

myth busters found that a tonneau cover was the same as a tailgate up, of course they tested at 55 mph, not realistic for the US, try it at 65 or 75 and the difference will show more.
My ranger shows a difference between the tonneau and the tailgate up, but I drive mostly at 75 on the highway (and get passed the whole way) of course I also have a bug deflector on the hood, I went through a windshield a year until I did, since then only a large washer made me replace one. They all cracked starting from the bottom up a few inches and then ran toward the middle. the bug deflector may be changing the airflow to the bed.
My dads ranger has the extended cab and he found no difference tonneau or tailgate.

[Larry C]

I have spent several hours searching truck forums and researching the Mythbusters findings as well as other more scientific ones. The amazing thing is all have different views, even Mythbusters did their test twice with different results each time.

However, no one I have found has done any PU bed testing while towing an aerodynamic trailer.

I just installed a Tonneau cover on my new PU. The PU only has 1k miles on it, and I haven't even checked MPG yet, but I just (today) returned from a 150 Mile drive with the cover on. I did the same drive 2 weeks ago, and on the same flat, long smooth road I traveled previously, I did notice a different tachometer reading between the two trips at 60 MPH.

I have been using the tach to watch shift points with my 5sp manual transmission as well as watching rpm's at different speeds so this slight difference (less than 100 rpm's) between with and without the tonneau, caught my eye.

I know there are so many variables, and my observation was not very scientific, but I am leaning toward the tonneau offering at least some help (lower RPM should equal lower MPG) for the PU only, but that may prove the opposite while towing a tear.

The tonneau is a roll-up type, and I can try the rpm thing over a given stretch of road on the same day with it on or off.
This could prove to be even more scientific than trying to accurately check MPG with or without the tonneau, and i'll try again when I actually finish my tear

Larry C