As some of you know, I tried to go down to southern Indiana last week to get the last of my furniture out of my house and close the deal to sell the house. As it turns out I didn't get down there, freezing rain (and getting seriously sideways with a trailer) convinced me that it wasn't worth the risk to get the furniture. But that isn't why I started this thread.

As I left the Appleton area, I noticed that the trailer seemed to be fighting the truck. I thought maybe I was bucking a headwind. At our first stop (wife averages 80 miles between potty breaks ). I noticed there wasn't a strong breeze. The trailer seemed unhappy, the faster I went the harder it seemed to fight the truck. Even a small vehicle beside it would cause it to bobble and sway. I knew this wasn't right, last year I towed the trailer 20,000 miles without any problems, but not that day.

Also, another clue was a large drop in fuel mileage. I usually get about 10 MPG towing my trailer empty, but now I was suddenly getting 7.3-7.8 MPG with an empty trailer.

At every stop I would search for a cause. My brakes were not dragging, trailer bearings were OK, trailer tires were OK, truck tires OK, truck was fine without the trailer, so just WTF was going on?

On the trip back, I started going over when I had last towed out on the open roads (not just backloads towing, but 60-65 MPH for hours on end), that was last fall.....and what had I done to my truck since last fall. In late fall, I put a hard bed cover on my truck.

I started thinking about what that does to air flow. Normally, with the cover, air would come over the cab, spill down onto the cover then slide off of the truck....but with a trailer it would seem the airflow would hit the trailer now. Without the cover, airflow would dip down further into the bed, then exit the bed at the tailgate, leaving a vacuum area behind the truck.

To test out my hypothesis, I took off the bed cover. I had to tow my trailer up to Wausa WI this morning with a 4000 pound load, then return empty. My trailer pulled easier with 4000 pounds in it and no bed cover than it did empty but with the bed cover! I was totally shocked at the difference. My mileage was back up around 10 MPG unloaded. It is like night and day. It didn't sway when a vehicle came beside it, it just seemed happy again.

So, is this a Super Duty short bed only thing? Has anyone else ever experienced this? I'm wondering if an air dam on top of the cover would deflect enough air.

 

I don't see the fallacy in your theory, but it still doesn't make sense to me. I don't understand how the empty bed would reduce the amount of wind hitting the trailer. I'll subscribe to this thread to see what others have to say.

What kind of MPG increase, if any, did you notice running with no trailer with the cover?

 

Without the trailer, I see a very slight increase in mileage with the cover, maybe .5 MPG.

 

It is interesting to see just what happens in the bed of a truck as one is going down the highway. By that I mean, have you seen what happens when someone has a piece of garbage in the bed of their truck (usually an empty cup or something. It does not get pressed flat against the tailgate as one might think. Instead, it swirls around, usually right up at the front of the bed, right behind the rear window! So when you think about this, the air comes over the cab, hits the tailgate, then swirls back towards the front of the truck, and continues that swirling. If you notice, a cup in the bed of the truck doesn't usually "escape" for quite some time, if it does at all. It gets pushed to the front of the bed, lifted, pushed back down, and so on.

With that in mind, I can totally see how your bed cap would affect the airflow negatively, as far as towing your enclosed trailer goes. As the air passes over the cab, instead of coming down and hitting the tailgate, it just goes right over it and slams into the front of the trailer.

Another one for Mythbusters??

 

Never thought about it but your theory makes since. I have also heard others say
their mileage went down with the cover, when not towing. Supposedly, the wind forms an aerodynamic cushion that lets the resistance pass over the bed, even better than a bed cover.

Good observation on your part,

 

It was already on Myth Busters...Kinda.....With an empty open bed, with tailgate on and closed, they got better mileage...then they went to the designers...With a regular bed, as the truck picks up speed, it creates a bubble of sorts in the bed, causing the remaining air to flow OVER the end of the truck, dropping a few feet behind it, (this also explains the swirly motion of paper cup in the bed). When they took the tailgate off, the wind would drop immediately behind the bed, actually "grabbing" the vehicle and causing lower MPG. Then the bed cover...Same thing...Would drop almost immediately...grabbing the truck...but more going past the end of the bed than without a tailgate...this could also explain your trailer getting squirrely...more air being push at it, could be getting under it or over it causing your symptoms.....Something to think about.

 

My F-150 got better mileage with the cover both pulling and not but as opposed to Redford's setup my trailer isn't a flatnose. They do make a removable wing that can be strapped on the roof but I have no experience with one other than on an 18 wheeler.

 

don't know if you ever noticed but lots of the stuff myth busters does only pans out for them,I finally gave up watching them,deeming the full of crap

 

Forget Mythbusters, unless they did exactly what Redford did, or what I do, or anyone here with an SD does, EXACTLY the same thing, it doesn't matter.

I wonder what you would get with a cab-height topper, or even one of those with the higher back-end that would sorta meet your trailer?

I've noticed over the 5 years I've had this truck, going over the same round-trip on Labor Day weekend and other times of the year, a total of about 10 220-mile, and another 10 500+ mile trips, that with the cap/topper, I consistently get .5-1MPG's better.

I have no doubt, Redford, that what you saw is legit, and I'd love to hear more about it as time goes on.

The closed-tailgate, high-pressure-area idea in the open bed, has definitely got something to it after all, doesn't it?

Every wheelbase, every cab length, every box length, is going to be different.

But oh boy, do I notice a difference with the cap/topper versus the open bed with closed tailgate.

 

I imagine using a topper with my trailer would be very beneficial, but then again I thought the bed cover would help, Art.

I mean, the difference with and without the cover is dramatic! I was hoping someone who tows on a regular basis and has a rollup cover could try it both ways and tell us teh results.

 

my topper is just above cab high
when I to my flatish nosed trailer I get so much turbulance that it will actually open the rear widow on the topper if I don't lock it
with the v-nose I don't get that
I actually thought of putting a deflector on the back of my topper

 

To my uneducated mind this makes the most sense. Of course we're assuming that the drag is all coming from the front of that brick he calls a trailer, and not from the wind affecting the top.

Have you considered taping a bunch of small ribbons or streamers to the front of your trailer and doing some test runs to see how the drag is affected? I'm thinking maybe tape several rows across the front of the trailer to see if you notice a difference in the point of impact. That is unless you know somebody that will let you borrow their wind tunnel.

 

It's amazing what a 1/2 inch tall strip across the rear of a race car will do for handling. Of course the superduty isn't going 180 MPH but there is a huge volume of air being displaced by this vehicle, and it's trying to get back into the void that the truck leaves behind. Wouldn't it be cool to put your rig in a wind tunnel just to be able to visualize what's going on. We would all probably be very surprised at the high and low pressure areas. Like, what happens between the truck and the trailer?

 

I'm sure taping a bunch of ribbons to my truck and driving down the road will somehow get me a ticket here in Wisconsin........LMAO. I may try that, need to do a little more towing Friday evening.

Interesting about the topper creating turbulance. I guess an air dam would benefit you.

 

wonder if you would get a similar effect without tailgate as with cover