jwt1603

I've got a F-250 with a hard cover on the bed. When I pulled an open trailer the wind resistance wasn't much of an issue with it flowing back over the bed and through the tire rack and past the car on the trailer.

Now I have an enclosed trailer (new 20 foot Haulmark, 2,800 pound car, spare tires, tools, etc. nothing extravagant) and my fuel mileage sucks. I realize that the enclosed trailer is heavier but would it help the air flow if I put a topper on the truck? That would seem to keep the air flowing more smoothly over the truck and then continue on over / around the trailer since the truck has already broken a hole in the air, kind of like drafting.

With the flat bed cover it would seem to me (no engineer) that the air smacks into the front of the truck, goes up over the cab, then creates a low pressure area behind the cab in front of the trailer. Then it has to hit the front of the trailer and go over and around that.

Any thoughts on this or would the topper just be a vain effort to save money on $3.00 a gallon diesel fuel? I may do the topper anyway because of the additional storage room but it would be nice to have a financial reason to do it.

By the way, my mileage without the trailer at 70 is 18 MPG. With the trailer at 70 it drops to 10. 2008 F-250 turbo diesel. I know it has the new EPA mandated fuel burn system but that just seems like a really big drop.

We do a lot of traveling to events so making up the grand or so for the topper in savings wouldn't take all that much time.

Thoughts on this?

Gary2KC5

Do you have a V nose or flat front?

If its a flat front its like pulling an 8'x8" plywood parachute behind your vehicle...not to mention the extra weight.

I have a 1500, with my 22' V noxe it puts the weights right at capacity.

My fuel milage is about 16 on the highway without the trailer 9.5 with.

davidfarmer

I have a V nose and a 3/4 ton yukon.......same issue. At 55mph it's fine, at 65-70 fuel economy drops to below 8mpg. I agree that with enclosed trailers, aero is much more of an issue than weight (power and economy wise that is)

Everett Ogilvie

While towing my 24 foot enclosed "sort of rounded but basically flat nose" trailer with my 2500 Duramax I was getting a little under 11 mpg at 75mph. I slowed to 68-69mph and got approximatley 2mpg more.

c4cruiser

A bed cover may help some but your enclosed trailer is like towing a brick. Some sort of aerodynamic nose on the trailer will help but as you mentioned, the additional towed weight is partly responsible for the loss in fuel economy.

Speed plays a part too. Try towing at 55 and see it that helps. A friend tows a 24' enclosed trailer with his GMC 3/4 ton and the DuraMax and Allison tranny. He gets about 11.5 to 12 MPG at 60. His trailer has a rounded aero nose and that was worth a good 1.5 mpg.

mousecatcher

absolutely. also get "air tabs" (google it) for the trailer.

Last C5

I have an F350 Powerstroke and the difference in gas mileage between 65 and 75 mph is amazing. I tow an open trailer with a Z on it now, but in my previous life I towed various horse trailers a couple billion miles. A cab high canopy does make a difference mpg, but it's pretty minimal.

Jason

Welcome to the world of enclosed trailers. Want another shock? Try towing it empty. Your fuel mileage will be about the same.

AU N EGL

11.5 mpg here with my 1500HD & 24" flat nose Pace.
Have to keep my speed to 55-60. Any more and the millage really drops

19.5 with out the trailer

jwt1603

I'll probably go ahead and replace the hard tonneau with a topper. I need the extra space anyway. It can't hurt the fuel mileage.

jwt1603

I was expecting a drop in mileage of course but jeez it seems extreme.

jwt1603

It's sort of a rounded front. Not flat but not a V-nose either.

Based on your numbers and others on this thread I probably shouldn't feel too bad. Seems like I'm in the ballpark for the amount of loss in mileage.

davidfarmer

I'd love to see more data on the air tabs...... Their data isn't very detailed, and not sure they would look so hot on my Yukon

jwt1603

Yeah, I played around with speed coming back from Darlington two weeks ago. The difference between 70 and 75 was huge.

I really don't want to go below 70. We travel a lot and typically fairly long distances. The 5 mph to drop to 65 adds up in time when going to South Bend, Indiana from Florida.

On shorter runs (maybe under 5 hours) I'll probably try 65 and see how it does.

brkntrxn

I think a topper would help. I am not an aero engineer, but it just seems like it would make sense that the air stream would not have a chance to come back "in/down" before getting to the front of the trailer.

I also have an 08 F250 diesel. It just hit 20k miles and the mileage has steadily gotten better since the 12k or so mark. Same as you, I get right at 18 avg when empty running 70mph. Anything more than 70 and the mileage starts dropping a lot. I can get slightly better running 65mph.

I own and currently tow my C5Z on an 18' open trailer. I generally get 14-15mpg as long as I keep it under 70mph. Anything more and the mileage drops like a rock.

On occassion, I have towed with friends enclosed trailers (20-24') and I firmly believe an open trailer is worth 1.5-2mpg over an enclosed. I usually average 11.5-12mpg when pulling enclosed.


-Kevin

69427

I make a lot of trips from Florida to the midwest, often using my trailer to haul non-automotive loads (I come back empty). My mileage is basically the same loaded or empty. Aero drag seems to be the key item when towing an enclosed trailer.
My present trailer is a Vee nose, while my old one was a flat nose. My previous fuel mileage 10-12 mpg. With the Vee nose trailer I get 12-14 consistently. The improved fuel mileage hasn't paid for the new trailer yet (), but it was a welcome surprise.

Kubs

Ok this may sound cheesy, but I think it would work better than air tabs.

What if in addition to a topper you make some sort of tarp that goes from the corners of the topper to the top corners of the trailer. It would need some sort of accordian style middle for turning but it would reduce drag by a quite a bit.

Im no fluids engineer, it was just a thought I had.

mousecatcher

http://www.solusinc.com/pdf/2003-01-3377.pdf

Gordy M

When you talk of Aero, I have a sloped nose 24' and when I towed with the 5.3L Yukon my mpg at 65 was in the 10.3-10.6 range. A friend who tows a 24' flat front with a 5.3L Yukon was consistently getting 95.-9.8 mpg.

Today I tow with I Escalade ESV (6000lb wind block), with tuning to both the trans and engine I get 10.5 to 10.8 mpg.

I don't know what the effect on towing but the "Myth Busters" did mileage test towing a truck with the tail up, the tail off and with a topper. They found no significant difference with tail or topper but slightly less mpg without a tailgate. Something about a boundry layer with the tail gate up that mimicked the effect of a topper. FWIW

mousecatcher

are you sure that was towing a trailer? pretty sure that was just the truck itself. if so, that's completely different.