Just finished an 1,800 mile round trip pulling a 16' enclosed trailer. Stayed at the speed limit over five states - speeds went from 60 mph to 70 mph. On the way up averaged 11.5 MPG - low of 11 and high of 12.2. I was hoping it would be higher.

Before leaving on the trip back I bought a piece of 4x8 1/2" OSB. Stuck it in the bed at an angle so that about 2' stuck out the back over the tailgate. Averaged 13.5 MPG with a low of 12.8 and a high of 14.6.

It cost me $8 for the OSB and I saved $54 in fuel on the return trip.

That is funny! I just did the same thing and noticed a substancial mpg gain. I opened my bed cover almost same as plywood. So that will be happening every trip now.

That may or may not have resulted in the gain in MPG. So many things effect MPG.

Aside from the obvious factors like speed, grade and weight, I have noticed that even slight wind speeds make a noticeable difference in my fuel mileage.

My travel trailer is square, wide ,and flat like a giant box which makes it very susceptible to wind conditions.

It seems pretty definitive. We picked up a headwind half-way through the first leg of the trip. That's when our MPG's dropped from 12 to 11. Didn't feel the headwind powerwise, but really noticed it with the milage drop.

No wind at all on the return trip so it sure looks like we gained at least 1.5 MPG's since even our average was higher then our best run on the way up.

Same drivers and same load, even similar temperature. Plus, most of the run was on cruise. Good enough results so that I'll probably make a slightly better deflector for future runs. From what I've researched, as long as you can make a clean air run within about three feet of the trailer it wil help. On the flip side, those big wings that you see mounted on the back of a truck cab are too far away from the trailer to be much good.

An all-out effort to reduce trailer drag might look something like this:
http://www.dieselplace.com/forum/attachment.php?attachmentid=66861&d=1211736893

More info on aerodynamic improvements here:
http://www.dieselplace.com/forum/showpost.php?p=2670519&postcount=60
http://www.dieselplace.com/forum/showpost.php?p=2670540&postcount=61
http://www.dieselplace.com/forum/showpost.php?p=2671195&postcount=62

Here's one fellow's less sophisticated home-built solution:
http://www.johnbridge.com/travel_trailer_aerodynamics.htm

I just installed airtabs yesterday to supposedly reduce drag on the back of my trailer (airtab.com)

The front of my TPD trailer is sloped back at the top, I noticed a big difference than the flat front Pace we had before.

Miniracer - How much did the air tabs cost? I've seen all kinds of info on their website but no $$$ figures.

$2.50 each

No quantity discount evidently, since a kit of 80 is $200, but the kit does include a spacing template.

http://www.buyairtab.com/

You might want to read the comments here:
http://www.woodalls.com/CFORUM/index.cfm/fuseaction/thread/tid/21345570/gotomsg/21377937.cfm

FWIW, I am not recommending Airtabs, as I have no first-hand experience with them.
I do know that tailcones work.

:nopics:
was plywood in bed/extended out between truck and trailer. think they call them vortec generators on aircraft, seen them on planes and helo's and always wondered, guess that answers that. have carried plywood sheets in back of s-15 years ago noticed lot of downforce and kept engine loaded, gained 2-3 mph for tack reading.

http://www.nishmotorsports.com/
These guys sell em. Go to the bottom of page "Vortex generators" I've used them and they do work. We have a 20' car trailer. My truck has a shell on it sometimes, it's a flat one. I'll leave the rear window on the shell open. I think it helps kick the air up and over the front of the trailer.

Miniracer - How much did the air tabs cost? I've seen all kinds of info on their website but no $$$ figures.

I just got the kit with 80 in it, for $200 plus a few bucks for shipping, I figured even if it helps a little bit, it is worth it. I used 64 of them on the trailer, I figured having a few left over for replacement would be a good idea, but you could save a bit if you did not need that many.

Here is a few more pics.

I wonder if you were to move the air tabs towards the front of the trailer if that would help. Or maybe run another row about half way. Vortex generators were originally desined to maintain laminar flow over a stalling wing. Air plane wings have them close to the leadine edge of the wing. To figure out were to put them you'd have to find out were the air is seperating off the trailer. You could do this by taping down ribons a foot apart or so front to back and 6" apart cross ways. Were the ribons start to move around and not uniform is were I'd think a row of generators would need to go. I'd imagine you coud mount a vidieo camera on the roof of the trailer and record as your going down the road at highway speeds.

If you were to add another row of airtabs, according to the manufacturer the place to put them is at the rear of the tow vehicle, so that the vortex they generate helps bridge the gap ahead of the trailer. They have some pictures of pickups & SUVs with airtabs on the back of them.

However, while that evidently works well when the tow vehicle closely matches the size of the trailer (as is the case with a 18-wheel tractor-trailer), the research I did indicates that to do that with a pickup in front of a normal cargo trailer, you need side and top extensions angled outward and upward. Otherwise there's too much offset.

All interesting comments on the aerodynamics of the truck and trailer combination. Anyone have a comparison on MPG with a tonneau cover vs. a full size topper?
I just bought an '08 and am debating on a tonneau cover (like I had on my last truck) or a full size topper. I pull a 25' travel trailer, just curious if the topper would be better as there would be less of an exposed front of the trailer to the wind.

i have a cap i run sometimes with my truck. i think i do get better mileage when i'm pulling enclosed trailers with the cap on vs. the cap off. i haven't done any actual mileage tests, but the next time i pull the combo i will definately check it out.