Aerodynamics of Truck Cap vs. Tonneau

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wayzgoose

Active member
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Feb 24, 2013
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I'm looking at towing a lightweight travel trailer with a Ford F150. I know I need the truck bed to store some of my life possessions. I know that if I use a cap, there's a lot of storage there, but I don't like not being able to see anything out my back window. I'd at least like to glance up at my rearview mirror and see the trailer is still there. So I was considering just putting a tonneau cover on the bed. That will still give me adequate storage and leave the rear window unobstructed.

It crossed my mind that I should investigate whether the tonneau would increase wind resistance against the trailer instead of keeping the vacuum high like a cap would. When you aren't towing, the reports I've seen are that aerodynamics and therefore gas mileage are better with the tonneau than the cap, but I wonder if that changes when you are towing.

Anyone have experience with this?
Thnx,
Wayzgoose
 
IMHO You will not see any difference with an open bed, a canopy or a tonneau cover in fuel economy.
 
Mythbusters did an episode on this and found that no cover, tail gate UP was better for fuel mileage (albeit not by much and for that specific truck).  I believe they put the truck in a wind tunnel as well.
 
My F-150 has a cap w/windows in front & back...I can see my trailer just fine..
I agree w/donn ...

George
 
Agree with all of the above.  You will be able to see your trailer out the back window (unless you have your stuff stacked to the roof of the cap) or the side mirrors and because the trailer is back there, you won't be able to see anything else anyway.  If it were me, I'd want the cap just because it is lockable.  I suppose you could get one of the fiberglass tonneau covers that lifts up and locks, but the cap seems to make more sense for your use.
 
Mythbusters tested a solo truck - putting a high trailer behind the pickup changes the aerodynamics quite a bit compared to solo running.

I have nothing to back this up, but it seems to me a cap would give smoother airflow up and over the trailer than a tonneau cover or an open bed.  Most caps have front and rear windows, so you'll still be able to see the trailer in your rear view mirror.
 
I think sans putting your entire rig in a wind tunnel, probably no way to know for sure what's best.  A cap may seem like it would smooth the flow over the trailer, but it may well do the opposite.

The only way to know for sure is to track MPG with and without.
 
Icemaker said:
My F-150 has a cap w/windows in front & back...I can see my trailer just fine..
I agree w/donn ...

George
I have a cap also and have the same experience as Icemaker.....

The thing is, the cap will add weight to the vehicle. That weight may offset any advantage to the "air-stream".

I also have a bed slide-out so that I don't have to crawl in the back of the bed to get stuff out. We love the cap on our truck. It also has tool boxes in the side to carry a lot of smaller camping gear.
 

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Research has shown that the towing vehicle and  trailer have to be no more than 30" apart for the towing vehicle to improve the aerodynamics of the trailer.
 
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