How much does a low roof rack effect MPG???

[One Awesome Inch]

I'm considering putting a roof rack on my Transit Connect on which to adhere my solar panel. The distance between the roof and the bottom of the panel would be about 2 to 3 inches. It will not be a large heavy duty rack.

Any idea how much the loss of aerodynamics would decrease my mpg?

 

[TrainChaser]

I don't know what I'm actually talking about, but the thought occurs to me that if it is literally a RACK, and the front isn't completely blocked, the wind should slide right through it. I doubt that the edge of a solar panel is more than 2", so that shouldn't create much drag. IMO.

 

[GotSmart]

I'm considering putting a roof rack on my Transit Connect on which to adhere my solar panel. The distance between the roof and the bottom of the panel would be about 2 to 3 inches. It will not be a large heavy duty rack.

Any idea how much the loss of aerodynamics would decrease my mpg?

Depending on how you mount the rack, from 1/2 mpg to 2 mpg.  

I only lost 1/2 mpg with my set up.  Extremely low profile.

https://vanlivingforum.com/Thread-Renogy-rooftop-installation-using-racks

In looking at the thread, the picture with the plywood on the racks was first attempt, and cost me 2 mpg.

The pictures below show how it looks now.

 

[Spaceman Spiff]

Any idea how much the loss of aerodynamics would decrease my mpg?

There are some dependancies to your question:

1. depends on how far back from the front the leading edge of the roof rack/solar panel is.
2. depends on the airflow profile over the roof of the van.
3. depends on direction/intensity of prevailing wind.
4. depends on if the roof rack/solar panels stick out over the sides of the van.

I have a pop-up camper on a pickup with solar panels 12" behind leading edge of camper, sticking up 2" in front and 3" in the rear.  Leading edge of camper is ~ 10" behind top of windshield; front of camper is flat.  That said, I get bugs all over the front of the camper and no bugs on the leading edge of the solar panels, leading me to believe that the front of the camper pushes the air over the panels.  I saw no decrease in MPG before and after solar panel install.

 -- Spiff

 

[LeeRevell]

How much it AFFECTS the MPG also depends on speed, miles driven, driving habits, etc.
All these will have their EFFECT on performance.

 

[SVan]

I have the same van, a 2013 Transit Connect with a Yakima roof rack on it. The bare rack (no solar on it as I use the rack for everything from transporting kayaks to attaching my DIY awning) does knock a mile or two per gallon off your fuel consumption (I get about 22mpg city/26 mpg highway) , but, as previously noted, it's not nearly as important a factor as speed. In 2015, drove from PA to Virginia Beach with two kayaks on the rack and average mpg was 24. However, much of the drive was on roads where the speed limit was 55-65mph. 

I got only 22mpg taking I70 across Kansas this summer on my way to Colorado because I was doing 75mph the whole way and often against prevailing winds. I tended to average about 23-24mpg in intermountain West driving as we camped all over CO, WY, MT, and ID this July/August. The weak link is the crappy four speed auto tranny. It sucks, but you already know that. Otherwise, it's an amazingly roomy box for a vehicle with such a small footprint and great turning radius. If you ever head into the mountains, you'll also find the short wheelbase and 7.5 inches of ground clearance will get you into most remote places.

 

[One Awesome Inch]

Thanks guys. So it's seems the best course of action is to keep the rack as low as possible and keep it as far back towards the rear as possible. I will endeavor to do so.

 

[BC Guy]

Have you considered flexible panels directly on the roof? They are more pricey.

 

[wagoneer]

While that is a very small point, i will accept you will lose MPG, don't think you will notice it's diminutive amount, MPO is keep her in tune tires at optimal and easy on the gas, under 65. Enjoy

 

[One Awesome Inch]

Have you considered flexible panels directly on the roof?  They are more pricey.

I have a 100w panel  on my current van. From what I've read they are not as efficient. Since the Connect is low-ish I also think that the rack would enable me to have  a bit more stealth than having a panel directly attached in plain sight.  I also like the idea of adding an additional 150w panel later on.

 

[One Awesome Inch]

100w *flexible* panel.

I wish this forum had better editing ability.

 

[akrvbob]

While I don't have any real data to prove it, my overall impression is that there is not much MPG loss from a ladder rack.

 

[Gary68]

a small rack with a couple solar panels= not much

a small rack with a canoe,2 ice chest and a couple bikes=alot

 

[flying kurbmaster]

you will loose some fuel efficiency with a roof rack at higher speeds due to foul air, at lower speeds you will loose some fuel efficiency due to the weight of the rack and the solar panel. how much? good question. I believe it is possible to increase you fuel efficiency by adding solar to a roof especially if the roof is flat to start with, if you smoothly tapered up from the front and tapered down to the back at between 12 and 15 degrees and extended out onto a camback along with rounding the sides. If, if you did this perfectly the gains you would make from airodinamics at higher speeds would outweigh the losses from the extra weight at lower speeds. Because you spend most of your time in the city I am not sure I would worry about it.

 

[BigT]

When I bought my 2010 Transit Connect it got 27 mpg on the highway and about 24 mpg in the city.  I honestly didn't notice a change after installing my Yakima rack until I added the kayak.  For some reason I never got around to figuring out just how much I lost with the boat on the roof, but I will.

I'm planning a trip to Mendocino in a couple of weeks and will track the mpg numbers on the highway when I do.  

My rack has a wing/air dam at the front to keep the air from passing under the panel or boat.  Not sure if it has any major effect.