Does wind deflector help mpg ?

[Alloy]

Consumer Reports looked at it

How Rooftop Carriers Affect Fuel Economy for Cars and SUVs

Consumer Reports tested the fuel economy on cars and SUVs to see how rooftop carriers affect fuel economy.

www.consumerreports.org

 

[javajoe79]

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

A couple grand in wind tunnel time should be all anyone needs for something this simple. That or real world experimentation.

 

[javajoe79]

It's also not always as simple as copying someone else with a different truck, rack, etc... Sometimes you could put a deflector on something but it does absolutely nothing because of the shape of the vehicle forward of the deflector.

 

[Mickey Bitsko]

Search 2019 dodge truck in a wind tunnel, good perspective ?

 

[billiebob]

Consumer Reports looked at it

How Rooftop Carriers Affect Fuel Economy for Cars and SUVs

Consumer Reports tested the fuel economy on cars and SUVs to see how rooftop carriers affect fuel economy.

www.consumerreports.org

THIS ^^^^^ many thanks for posting something with real research. My son bought an Impezza Wagon with a Thule..... one trip and it was in the garage. BUT if we really cared about gas mileage we would never "upgrade" the tires or lift the suspension. I went from 33x10.50R15s to ultra skinny and light 7.50R16s, technically 31s, and gained 5mpg on my brick of a TJR. And yes, fully 5mpg cuz I now commute to Calgary on a single tank, I could never do that with 33s.

Honestly, we could care less about fuel economy, we might care about range but everything we do kills fuel economy.

 

[billiebob]

I have mixed feeling about the test by Consumer Reports. I can create a test to show what I want to show and get the results I want. If you take and open a window on the vehicles Consumer Reports tested and stuck your arm out the window and did a test,you would probably get the same results. Testing with a full size truck or large SUV the percentages will drop considerably.

Think of a vehicle that gets 12 MPG and compare that to a vehicle that can get 50 MPG. Put the same drag on the vehicles the %) MPG vehicle will feel the drag at a higher percent then the 12MPG vehicle.

Of all the testing done, I kinda trust Consumer Reports..... A key to evaluating the level of trust is reading the ads in tha same issue, If the testing says the hottest most reliable overlander is a Lada Niva and the mag is FULL of Lada Niva ads..... I'd bet the testing was biased...... Consumer Reports seems to distance themselves from that bias.

Paranoia kinda builds mistrust and conspiracy theories, sometimes ya have to use common sense and this particular testing report by Consumers Distributing is pretty accurate especially since my sons Imprezza purchase. I think he would say it is a conservative result.

 

[Mighty Dodge Ram]

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.

I didn’t miss the point, I just wasn’t clear in my reply that in my experience (driving pickup trucks and suvs with roof racks) wind deflectors do not increase fuel efficiency appreciably but rather that speed (reduction) is a greater factor. But I do agree with the comments re: noise, bugs, etc. And yes, the heavy trucking industry has adopted many aero packages which save fuel/$$$ over millions of miles. My cousin tells me it’s in the thousands of $$$ in annual fuel savings. ?

 

[Porkchopexpress]

Think of a vehicle that gets 12 MPG and compare that to a vehicle that can get 50 MPG. Put the same drag on the vehicles the 50 MPG vehicle will feel the drag at a higher percent then the 12MPG vehicle.

Definitely. Even between sedans and small SUVs in the CR test, the % drop with just the rack was much higher in a sedan. That's also why electric vehicles go to such lengths to be more aerodynamic and have less rolling resistance with narrow tires.

 

[GBGCR4x4]

THIS ^^^^^ many thanks for posting something with real research. My son bought an Impezza Wagon with a Thule..... one trip and it was in the garage. BUT if we really cared about gas mileage we would never "upgrade" the tires or lift the suspension. I went from 33x10.50R15s to ultra skinny and light 7.50R16s, technically 31s, and gained 5mpg on my brick of a TJR. And yes, fully 5mpg cuz I now commute to Calgary on a single tank, I could never do that with 33s.

Honestly, we could care less about fuel economy, we might care about range but everything we do kills fuel economy.

Great analysis on the 33s. Most of what I've added has "killed" my fuel economy. I have a Front Runner Slimline that used to have a wind deflector, and a Guana Equipment tent on top. The wind deflector reduced the noise quite a bit, but the moment I changed tires and suspension, the gas mileage simply changed. I've also added a lightbar after that, so the wind deflector is gone, and honestly the only way to save on gas now is driving slower.

 

[lugueto]

In my experience, yes. Fairings work. I can't say exactly how much mpg's you get back, but anything is better than having the RTT dragging in the wind.

Fab up something, attach it to the roof rack flush with the tent. It won't be perfect aerodynamically, but it WILL be better than not having it. And the difference while driving is certainly noticeable.

Great analysis on the 33s. Most of what I've added has "killed" my fuel economy. I have a Front Runner Slimline that used to have a wind deflector, and a Guana Equipment tent on top. The wind deflector reduced the noise quite a bit, but the moment I changed tires and suspension, the gas mileage simply changed. I've also added a lightbar after that, so the wind deflector is gone, and honestly the only way to save on gas now is driving slower.

You know its when you start realizing that they go hand in hand that range is incredibly increased.

We didn't care much for efficiency or range a few years back. Due to fuel shortages our solution for range was simply carrying more fuel. When the fuel prices went up, we quickly knew that our inefficient vehicles had to go on a diet, or they simply had to go. Drastically changing driving habits (and said diet) improved our efficiency enough to improve our range up to 30%.

Where we saw the most difference, without a doubt, were tires and roof racks/ tents. I agree on everything we do negatively affects fuel economy, but you can reduce tire size a little without affecting clearance or traction too much while drastically improving drivability and efficiency. And roof top tents can be replaced with regular ground tents, or you can add fairings and compromise. But anything is better than doing nothing.

 

[billiebob]

In my experience, yes. Fairings work. I can't say exactly how much mpg's you get back, but anything is better than having the RTT dragging in the wind.

Fab up something, attach it to the roof rack flush with the tent. It won't be perfect aerodynamically, but it WILL be better than not having it. And the difference while driving is certainly noticeable.



You know its when you start realizing that they go hand in hand that range is incredibly increased.

We didn't care much for efficiency or range a few years back. Due to fuel shortages our solution for range was simply carrying more fuel. When the fuel prices went up, we quickly knew that our inefficient vehicles had to go on a diet, or they simply had to go. Drastically changing driving habits (and said diet) improved our efficiency enough to improve our range up to 30%.

Where we saw the most difference, without a doubt, were tires and roof racks/ tents. I agree on everything we do negatively affects fuel economy, but you can reduce tire size a little without affecting clearance or traction too much while drastically improving drivability and efficiency. And roof top tents can be replaced with regular ground tents, or you can add fairings and compromise. But anything is better than doing nothing.

yep, tires were a game changer for me....
with 33/10.50R15s I got a best of 17mpg if i never exceeded 55mph.
changed to lighter, super skinny 7.50R16s, technically 31/7.50R16s.... the most popular tire in Africa....
and I gained 5mpg, by a 19 gallon tank that extends my range 95 miles.... that is huge.
from 323 miles to 418 miles..... and proven by the 300 mile commute I do often.
I never made Nakusp to Calgary without refueling, I do it all the time now.

Speed, yes a factor, I rarely pass and never go over 60mph.
Tires and speed are the biggest factors affecting range.
Aerodynamics are a factor only at higher speeds.

If you have an RTT and 35s and you like 75mph Interstates you are gonna suck a lot of fuel..... even with wind tunnel developed fairings.

 

[Wilbah]

Aerodynamics are a factor only at higher speeds.

Yep to this- the reason the Veyron's and similar supercars are breaking 1,000 HP is they need the approximately extra 200+ horses to get from 175 mph to cross 200 mph. The wind resistance at 190 mph is astonishingly "stronger" than at 140 or 100, etc. Same from 60 to 75 for high profile vehicles like trucks and SUV's.

 

[brycercampbell]

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

Probably more economical to rent a wind tunnel than buy a sheet of 4x8.

 

[Zuber]

The best method to improve aerodynamics is to start at the back. Close the profile of the car smoothly.
I would be good to get a picture of the OP's vehicle.

 

[billiebob]

The best method to improve aerodynamics is to start at the back. Close the profile of the car smoothly.
I would be good to get a picture of the OP's vehicle.

yep, often what we ignore is more important than what we focus on