Drag ?

[Impulse24]

I thought of putting this in the DIY section but thought it belonged here as it is a 5th wheel question.

There has been many topics of does a wing benefit towing, and when everything is take into account there is still those who reject the idea and those who accept it with glee. Yet tires and driving style can either destroy or increase MPG plus every picture of a wing shows it is too far forward in relation ship to the front cap of the 5th wheel to give any benefit.
There are also discussions on tail gates down or tailgates up, should it be left off or use a louvered tailgate? I guess security of what you carry in the bed also comes into the scenario.

But overall drag is rarely questioned, So here is a problem I can't seem to get answered and would appreciate a little help with.

Question,

I have a sliding bed cover, If I slide it over the front half of the truck bed (in front of hitch)when towing a 5th wheel with the tailgate up ! And rear of the truck bed behind the pin is left open, is more drag created? Is it the same amount of Drag as a full open bed? Or is there less drag?

Thanks.

[BarneyS]

Too much flaming going on. Thread closed.

[Redwoodcamper]

The "economy" of saving a few miles per gallon doesn't add up if it costs me a significant amount of time to research and achieve. A relatively small amount of work nets me far more $ for fuel than the costly loss of time and energy to possibly get slightly better mileage. Everyone sense of value and economy is different.

[tinner12002]

Impulse24 wrote:
Prior to buying a MH I asked a round about many things, including fuel consumption, the favorite response was from people like you who always replied "If you have to ask, you can't afford it " Yet those same people complain about a 15 cent nut and bolt. If you don't know what your average MPG is you have no idea if you have a problem developing, which can add up to a few thousand dollars in repairs.
Besides A good Driver works out MPG with pen and paper, as they do other costs, only and idiots drives around unaware of expenses. I'm sure you could learn a few economic solutions if you were to go grocery shopping with your other half !!!
And if you have money to throw away then I suggest you pick a worthwhile charity and make a monthly contribution.

In answer to your question, I doubt how open or closed your bed cover is, will make much if any difference in MPG as others have also stated. I think your way over thinking/worrying on the whole issue in my opinion.
As for calling people idiots because they aren't as concerned about various aspects of their travels I think is a bit much. Personally, I don't pencil figure my mileage ever, I look and rely on the onboard to guestimate my trucks info and do complain sometimes because of the high cost of things as well as probably most people do. I'm not too concerned about the MPG I get, if I was worried about it I'd be driving a Prius pulling a 200lb camper. Those people complaining about a $2 bolt might be more attuned to their expenses than you might think. Others may be thinking the same of you by you worrying about .2 of a MPG.

[IBcarguy]

Impulse24 wrote:

IBcarguy wrote:
How would you ever know? Wind tunnel test? I'm no authority on this topic but I think it would be negligible and maybe not even measurable. I guess you could try checking mpg with it open compared to closed. There are a lot of other things that would impact MPG rather than your sliding bed cover.
The wing, however might help especially if your 5th wheel cap is rather flat. Mine is very rounded and curved and I doubt if a wing would reduce wind resistance very much.
I think slowing down to 55mph would have the greatest impact on fuel consumption.

I appreciate the reply, and fully understand your point, however a study at Institute of Fluid Science Tohoku University 2-1-1, Katahira, Aoba-Ku, Sendai JAPAN, Using a wind tunnel showed that a short bed truck had little effect on drag and a large bed truck created a lot of drag while and driving with the tailgate down was even worse for both vehicles. The Geometry of the Truck Bed also made a difference, but as most truck beds in the USA are within the same geometry field I don't see a big comparative difference.
I'm my scenario, I am in essence reducing a long bed to a short bed, but the area behind the cab to where it becomes a short bed is a question I don't have an answer for, nor does this study give any idea of how the drag is increased or decreased when a trailer is attached.
The wing, as has been stated many times does work, If it didn't the Commercial Industry would not be using it, Plus assuming all other aspects are in tune and maintained the distance between the wing and the trailer is the biggest determining factor of efficiency. I agree that a cap with a curve is more stream lined than a brick wall cap, and there are caps with contorted shapes creating a stream line effect. But again the distance between the back of the truck and the cap on the trailer is an unknown..
In theory it should reduce drag I guess trial and error will provide the answer...

Thanks

I'm not so sure the test comparing a short vs long bed truck is valid when a large 5th wheel trailer is attached over the bed of the truck. I would think that this large mass would disturb a lot of the air stream and subsequent resistence issues....but I'm no scientist. If you think it might make a difference, do some testing.

[FF286]

I had a 98 sandpiper with a flat nose, I hated pulling that trailer, that I pulled with an 02 2500 Silverado. Empty I averaged 19 mpg, towing the camper 7 mpg. One trip to Florida I took the tailgate off and got between 9-10, and anything in the bed stayed put. Before I started removing the tailgate once I had put the kids basketball in the bed and had to stop and get it because the air turbulence sent it flying going down the road.

[pickjare]

It seems to me like the area of the bed directly behind the cab is kind of a dead space anyway. I have noticed the loose end of a piece of rope will gently (as opposed to vigorously) blow around that area. It's also the best place to ride if your going to ride in the back. There is nothing causing resistance in that area to the truck moving forward down the road, so I wouldn't think covering it will matter at all. But things have to be tested in order to prove. I agree with "Old Biscuit," his idea will tell you the difference, if any, in wind resistance. Also it will change with vehicle speed, so if it were to be done, I would start measuring deceleration from the highest speed you can reach down to the instant vehicle falls below say 35mph.

[Impulse24]

B.O. Plenty wrote:
It takes about 8 more miles per gallon to tow my fiver than the truck gets without it. Even a probably unattainable, 20% increase or 1.6 mpg, in fuel mileage doesn't amount to much in the grand scheme of things.

B.O.

I'm not finding fault, but Surly you mean you loose 8 miles per gallon towing a 5th Whl ?

And assuming you increased mpg by 1.6 it has to be worth travelling a little longer between fill ups ? On a tank of Gas that's +/- 32 miles extra travelling before stopping for a refill of jungle juice. Which also equates to 4 gals of gas. It may not seem much but when fuel costs were running at $5 gallon thoughts changed. I have also toyed with making my own Aluminum wing which would also cut down costs. the problem is mounting it so it would be able to lay flat when needed and upright for towing.. But that's another project.. As is stopping people from hitting a tail gate when hooking up..

Without the trailer I average 11.8 mpg, pulling a trailer I average 8 at best, so any improvement is acceptable..
I have a 1 ton GMC Dually with a 454, an excellent truck although the MPG stinks. Why not buy a Diesel I hear you ask, Simply I am not as wealthy as those who have no idea what their MPG is and complain about a 15 cent nut and bolt ! Although I will accept a freebie from him !!
Returning from TX a couple of days ago I averaged 8 MPG, and although GM say use 87 octane, I was using 89 octane which gave a little extra power.
So I seek a to streamline and drive economically 55 - 60 MPH. Being retired I have all the time in the world to get to a destination, and I enjoy the scenery much more than the Speedy Gonzales' who like to fly by me.

I appreciate your reply.. Thanks

[STBRetired]

I think the biggest difference in mileage will be determined by speed. If I drive my MH at 55 - 60, I get 9.5 mpg without the toad. When I drive 65 - 70, I get 7.3 mpg. Determined on a 140 mile trip on same road with minimal elevation change and side wind on both.
My son drives for Nussbaum Transportation and they determined that using trailer skirts and trailer tails improves fuel mileage by 0.2 mpg. If you're driving millions of miles per year across a large fleet, that is significant. Getting similar improvement on an RV might not be able to offset the cost of the installation of the aerodynamic devices in a reasonable amount of time. Nussbaum found that separating the turbulence from the back of the trailer with the trailer tail has a larger impact than keeping the air out from under the trailer. I doubt that you would want to install one of those on your fiver, but you might want to consider a flat spoiler on the trailing edge to separate the turbulence at the back, Using a vertical spoiler at the rear of the fiver would generate downforce which could result in uneven pin loading.

[oldbird1965]

I used a wing for years and I can say for sure it works. I have less bugs to clean off the cap, lol!

I also use the cruise control when towing, it uses lots of fuel but my right foot loves it.

[B_O__Plenty]

It takes about 8 more miles per gallon to tow my fiver than the truck gets without it. Even a probably unattainable, 20% increase or 1.6 mpg, in fuel mileage doesn't amount to much in the grand scheme of things.

B.O.

[Impulse24]

I'm not confused at all, I have already stated the biggest problem with most wings are they are too far away from the trailer to be effective.
Another situation with a wing is very few are set to the right angle, causing a futile fit. May be just may be RZv'ers with wings should also incorporate a faring on each side of the truck to push the wind a way from the sides of the trailer!.
Again a little pen and paper will help you work out the ideal angle and hight and width required. If done right there will not be a bug line !!! But all this is getting away from the original question.

[fj12ryder]

Impulse24 wrote:
I appreciate the reply, and fully understand your point, however a study at Institute of Fluid Science Tohoku University 2-1-1, Katahira, Aoba-Ku, Sendai JAPAN, Using a wind tunnel showed that a short bed truck had little effect on drag and a large bed truck created a lot of drag while and driving with the tailgate down was even worse for both vehicles. The Geometry of the Truck Bed also made a difference, but as most truck beds in the USA are within the same geometry field I don't see a big comparative difference.
I'm my scenario, I am in essence reducing a long bed to a short bed, but the area behind the cab to where it becomes a short bed is a question I don't have an answer for, nor does this study give any idea of how the drag is increased or decreased when a trailer is attached.
The wing, as has been stated many times does work, If it didn't the Commercial Industry would not be using it, Plus assuming all other aspects are in tune and maintained the distance between the wing and the trailer is the biggest determining factor of efficiency. I agree that a cap with a curve is more stream lined than a brick wall cap, and there are caps with contorted shapes creating a stream line effect. But again the distance between the back of the truck and the cap on the trailer is an unknown..
In theory it should reduce drag I guess trial and error will provide the answer...

Thanks

I think you're confusing the wings you see on trucks pulling 5th wheels with the wings/streamliners seen on semis. The wings on pickup trucks are too far away from the front of the trailer to help much, if any, at all. The "wings" on semi trucks are almost touching the trailer and are of the same height. They will work, wings on pickups not so much.

[cbshoestring]

Myth busters tested tailgate up, tailgate down and tonneau cover. Up got the best mpg...something to do with lift caused by the vortex of air circulating within the bed.

Not sure how having a 5er attached would change the outcome.

[Impulse24]

IBcarguy wrote:
How would you ever know? Wind tunnel test? I'm no authority on this topic but I think it would be negligible and maybe not even measurable. I guess you could try checking mpg with it open compared to closed. There are a lot of other things that would impact MPG rather than your sliding bed cover.
The wing, however might help especially if your 5th wheel cap is rather flat. Mine is very rounded and curved and I doubt if a wing would reduce wind resistance very much.
I think slowing down to 55mph would have the greatest impact on fuel consumption.

I appreciate the reply, and fully understand your point, however a study at Institute of Fluid Science Tohoku University 2-1-1, Katahira, Aoba-Ku, Sendai JAPAN, Using a wind tunnel showed that a short bed truck had little effect on drag and a large bed truck created a lot of drag while and driving with the tailgate down was even worse for both vehicles. The Geometry of the Truck Bed also made a difference, but as most truck beds in the USA are within the same geometry field I don't see a big comparative difference.
I'm my scenario, I am in essence reducing a long bed to a short bed, but the area behind the cab to where it becomes a short bed is a question I don't have an answer for, nor does this study give any idea of how the drag is increased or decreased when a trailer is attached.
The wing, as has been stated many times does work, If it didn't the Commercial Industry would not be using it, Plus assuming all other aspects are in tune and maintained the distance between the wing and the trailer is the biggest determining factor of efficiency. I agree that a cap with a curve is more stream lined than a brick wall cap, and there are caps with contorted shapes creating a stream line effect. But again the distance between the back of the truck and the cap on the trailer is an unknown..
In theory it should reduce drag I guess trial and error will provide the answer...

Thanks