Does wind deflector help mpg ?

[CraigW]

So, i have a 2019 Ram Cummins. I also have a larger 23Zero Walkabout 72 RTT. With that I originally had on a traditional bed rack which put the tent above the cab when traveling. I suffered 2-3 mpg loss. So, I then changed out to a lower rack which was about 12" high and put the tent right at cab height. On the lower rack my mpg came back. Down side is when using the tent i hit my head on the platform 1000 times. Therefore Im leaning to put back on the standard height rack. I am wondering if installing a wind screen to push the wind over the RTT would help the mpg. With diesel at $100 a tank makes me consider things. Then again if im going to spend $1000 for a roof rack and deflector i have to think.

Thoughts, experiences?

 

[Peter_n_Margaret]

If you spend a couple of million dollars to do a proper airflow analysis (like F1s and the like) then you could probably save some fuel, for sure.
Slapping on something that "looks like it will do to job" is likely to be a waste of time and money and may make it worse.
Cheers,
Peter
OKA196 motorhome

 

[86scotty]

If I am understanding you right there is basically no wind deflector that will help. You are flying in the face of millions of dollars in development by the OEM to make the truck as fuel efficient as possible by putting a big brick on the roof of the cab.

 

[Wilbah]

Make one out of plywood or similar and see if it helps. Cheap enough to determine before spending $ on something that doesn't work.

 

[Alloy]

How much does driving slower save

 

[NatersXJ6]

Having a bed rack that raises and lowers is probably more effective than a wind deflector, although more expensive. Some foam on the edge of the tent might be cheaper and easier.

 

[Porkchopexpress]

The airflow across the roof of the truck creates a turbulent layer starting at the top of the windshield. For a wind deflector to have a noticeable effect, it would probably have to be close to where the separation of laminar and turbulent air starts. Look at semi truck cabs and how they design aerodynamic body panels.

Edit: It still might not make that much difference and it would be ugly in my opinion.

 

[jadmt]

I found it crazy that my gfc camper did not affect my mpg all that much. Did several round trips ~440 miles ie missoula to bozeman and back on the same course with and without and was always close. The guy that bought my camper said he removed his lower bumper air dam before his trip up from Texas and said he took a noticeable hit on mpg.

 

[Mighty Dodge Ram]

Agreed with the comments on speed being the biggest factor. I get better mpg pulling a low utility trailer 55-60 mph vs no trailer 65-70 mph.

 

[JaSAn]

Lowering your speed misses the point:
-- Will I get better gas milage at a lower speed with a wind deflector?

Semi tractor manufacturers claim 5 - 10% increase in fuel milage with their aerodynamic packages, with 3 - 6% claims from the roof fairing and side extensions. FedEx and other major carriers must have data to support that because they buy the packages.

Vehicle roof wind deflector manufacturers claim up to 3% improvement while pulling a travel trailer.

Consensus seems to be on Wander-the-West is that a roof deflector reduces wind noise and bug guts but has no noticeable effect on fuel milage for slide-in pop-up campers.

 

[billiebob]

Air deflectors need a close fit to whatever you are trying to streamline.
A big gap from the top of the deflector to the loaded rack might create more drag.
Same at the leading edge the gap from the top of the windshield to the leading edge of the deflector is critical.

Speed is definitely the big factor and the reason the USA had the double nickel speed limit during the 1970s gas crisis.
Equal to drag at the front is drag at the back. An egg is the best shape. A box van the worst.

ps, commercial carriers are adding aero aids based on wind tunnel testing and most commercial trucks are governed you cannot compare anything built in a driveway added to an overlander with toys hanging off it to anything engineered for a commercial hauler. Most everything we do is based on gut feeling, not science.

Years ago I saw some testing done on pickups, they used a Syclone. They added a canopy, tonneau cover, sleeper extension thing, tailgate up, down, removed, plus a few odd partial box covers. Best gas milage was with a cover over the rear 1/3 of the box, front 2/3s wide open. No one does that tho.

 

[WVI]

Slim Patatoehead recently made a vid using a snowboard btw his vehicle and travle trailer. If I recall correctly, it saved him milage....

 

[MOAK]

I have a rack up top of my Landcruiser. A solar panel is mounted in the front. Utility boxes etc, cover the back of the full length rack. For a couple of years I went with the solar panel mounted flat, then tilted it up at camp. Being from the transport industry I tilted the solar panel high enough to deflect the wind up & over the boxes. It doesn’t seem like much but on our trips instead of averaging 11.5 mpg, we now average 12. Take a look at “ hot shot “ pick up trucks. They don’t put that air dam up there for looks.

 

[Porkchopexpress]

Semi tractor manufacturers claim 5 - 10% increase in fuel milage with their aerodynamic packages, with 3 - 6% claims from the roof fairing and side extensions.

So maybe 3% if you get a roof fairing that matches your vehicle profile and rack height well, that's $30 for every $1,000 spent on fuel. Semi trucks drive a lot of miles and burn a lot of fuel. They probably recoup their investment in aero packages pretty fast. Not sure how the math would work for the OP.

 

[Porkchopexpress]

I have a rack up top of my Landcruiser. A solar panel is mounted in the front. Utility boxes etc, cover the back of the full length rack. For a couple of years I went with the solar panel mounted flat, then tilted it up at camp. Being from the transport industry I tilted the solar panel high enough to deflect the wind up & over the boxes. It doesn’t seem like much but on our trips instead of averaging 11.5 mpg, we now average 12. Take a look at “ hot shot “ pick up trucks. They don’t put that air dam up there for looks. View attachment 690722

Roughly 4%. Matches the manufacturer claims of 3-6%