IsItFast

I have a 30ft toy hauler (tow behind) that I tow about every other month on about a 5-6 hour trip. While the truck has no problem towing it, the wind resistance it horrible. The trailer loaded weighs well over 10K lbs. But even going down hill a lot of throttle is required due to the wind. I am lucky to see 7mgp. The truck pulls great when there is a little wind or a tail wind. Otherwise the truck is constantly shifting in and out of OD no matter what the speed. Is there anything I can do to to help out the aerodynamics? Some type of spoiler/wing to add to the truck or trailer? I really don't want to add something permanent to the truck since it is only used for towing a handful of times per year.

Please read all the responses BEFORE you make a post. I appreciate all the help but I am not asking what is wrong with my truck. This is an issue of aerodynamics. The truck only has a few thousand miles on it and the wind drag, downshifting and poor MPG existed long before ANY of the mods were done. The trailer is also new. And when I sometimes change direction (say heading North to heading East) the trailer pulls just fine.

Here is an image from the first time I pulled it bone stock:

Hunter11

IsItFast, I have about the same mods as you do and I am pulling a 32' 5th wheel that weighs in about 10k and I have no problem with the truck shifting in and out of OD and I am getting 11 mpg at 65 mph. Could it be the 22.5" wheels and tires have changed your gear ratio? I have no clue other than that.

FiverBob

Wow, you have something wrong. I get 12mpg with a 16,000 pound fiver on the back at 60 - 70 on the interstates. Tires and 3.73 sure can't be helping.

Bob

FAY

All the symptoms are indicating an extra resistance to forward motion that are related to aerodynamics, as you have already pointed out. You do not need to look for any other reason until you first try providing less frontal air resistance, regarding you towed and towing unit. The only alleviation for the increased load placed on the truck engine must be as you said from a deflector/director in order to pass air over the top of the trailer rather than, as is happening presently, with air deflecting against a solid wall in effect.

The shape of the new Dodge trucks is fairly aerodynamic as a test in a wind tunnel would show. If you placed a swept back deflector/director at the correct angle on the roof of the cab the air would sweep over the windshield with an upward component that would lift further easily over the trailer if a somewhat high deflector was present. The deflector could be anchored to the front stake pockets in the box. The support against the horizontal wind component could come from braces to the rear box stake pockets. There would be termendous air pressure on the deflector and more support probably would be necessary. I am just giving you some ideas as I have had absolutely no experience with solving this problem regarding a pickup truck.

xyzer

Isitfast...........I have to go with the tire size !!...also if it is hunting in and out of OD you should lock it out.....!! or so the manual says! Do you still have the stock wheels and tires......that would be the easiest test or fix.....

IsItFast

I should state that I had this problem with the stock tires too before everyone says that this is the problem. There are pluses and minus to the larger tires as I will explain below.

This is running in the 75-80 MPH range on the highway which was not really good with the stock tires due to the high RPM's. MPG would be much better if I would drive a little slower with the stock tires. The difference was that with the stock tires had to wait until about 69 MPH before it would downshift. With the larger tires it will downshift at about 75; this causes a lot more frequent shifting. The larger tires have actually helped MPG somewhat since I have the right (lower) RPM at 75-80. As stated above it tows just fine as long as the wind isn't against me. But now I don't have the option to run at a slower speed in OD; it will stay in 3rd at speeds below 70. BTW. This is an 05 so I can not "lock out" OD....I am stuck with it or 2nd gear.

A fifth wheel in my opinion will have less wind resistance since it is in the air pocket of the cab. This is why I am asking about aerodynamics. As FAY has pointed out this seems to be the problem I am trying to solve.

RickG

The other posters are correct saying it's something other than wind resistance . I got 10-12 mpg pulling trailers larger than that . What is your mpg when not towing ? Just an off topic note about the tailgate up / tailgate down controversy - Mythbusters tested this . Two identical F150's were loaded with the same amount of gas and driven under the same conditions . The one with the tailgate down ran out of gas 30 miles earlier . Airflow test show with the tailgate up air spins down in the front of the bed and flows up over the tailgate . With the tailgate down airflow pushes down on the rear of the bed and tailgate causing drag .

Scotty

If your trans is hunting that much, I would venture a guess that it is slipping as well. Hence the mileage hit. Address the transmission. Even with just the EZ with that kind of rolling resistance, I bet there is some heat damage and other issues that would be resolved with some work on that trans. It may have been a dud from new anyway.

Scotty

FiverBob

When you play, you pay. You didn't originally state you were running 75 - 80 mph.

I ran some tests with my fiver - - note, fiver - - much better aerodynamically than what you are towing. On a level section of interstate with little traffic I would set the OH calculator and run at 70 for ten miles and see what it read, then again at 75, and again at 80. At 80 mph I was getting around 8.5 to the best of my memory. Once I go over 65 my mileage starts down fast. Wind resistance is not increased linearly with an increase in speed, rather exponentially. Small increases in speed create large increases in resistance. You need to decide what is most important - - speed or mileage.

Bob

Strick

I have a 24' toyhauler and I have noticed the same numbers. If I go over about 1700 rpms (about 63 or 64) the mileage really drops. If I try to do 70+ i get about 8mpg or worse, at 63 it get around 11. It is all about the aero. The way I look at it a fifth wheel gets hit be the wind alot different than a tag trailer so you really can't compare them. The wind is already getting lifted off the roof line of the cab so it can flow easier over the nose of the fiver. When pulling a tag the wind wraps around behind the cab and bed and hits the trailer dead on. I left one morning and there were tons of bugs out, it was amazing to see exactly how the air was hitting the trailer based on the bug splats.

When guys tell you what mileage they are getting and they just tell you the weight make sure you ask what kind of trailer.

tobyw

FWIW, I achieved a relatively substantial increase in mileage when towing my bumper pull toy hauler this summer by having the bed full of stuff. The trip was ~2200 miles total, and I was a good 3500lbs heavier than I had ever been loaded with the toy hauler (had the Jeep inside this time, instead of the ATV's). The bed of the truck was loaded with extra tires, fuel cans, generator, tool boxes, and a large cooler. From the very first fuel up on that trip, I noted about 1.5mpg BETTER than the last time I had towed the toy hauler, and as I said I was much heavier this time even. The only thing I can think is that the air was not swirling all the way down in the bed, but was bouncing off all junk in there. Maybe some sort of bed cover or canopy would solve your problems?

FiverBob

Good point, Toby. The wind tunnel tests prove a bed cover improves mileage quite a bit on a pickup alone. I see no reason why it would not help here.

belfert

I have a 28 foot toy hauler travel trailer. It too is a pig on fuel. I;m not down to 7 MPg, but 8.5 MPG is about as good as it gets.

I think the trailer simply has too much wind resistance.

Brian Elfert

FAY

You could put a canopy on your box with a very high roof line at the rear. The canopy roof would be aerodynamically graduated from near cab level to much higher at the rear. Maybe a swept back deflector/director from a point before where the canopy roof top start to be the heighest until some location near the rear bumper could be rigged up. The main supports for the deflector probably could come from a fabricated frame connected to the bumper or the trailer hitch.

Your high speed is sucking the fuel dry due to increased wind resistance and your oversized tires are acting like an auxillary transmission in high range. You could probably have more practically made use of an auxillary high/low range tranny instead of the larger tires.

IsItFast

Let me explain ONCE AGAIN that this is not a problem with the truck. It only has 3000 miles on it and the wind resistance problems were happening BEFORE the tires, EZ or any other mods were installed. The truck rolls along great unloaded or even when I am towing a few thousand pounds on a flat bed.

My unloaded milage has actually increased at 75-80 since my RPM's are lower now. I understand that at high speeds I am going to have to "pay the price" but I am not looking for answers for what is wrong with my truck.....as the title says I am looking to improve aerodynamics. Surely someone sells something that would help. I really can't afford to add something to the bed since I have a tool box and I usually have an ATV in there too.