How much will my MPG be reduced with plywood on a roof rack?

[MikeRuth]

From the photo I see Bob has the same Rack I do. for those who asked about it lifting the van. seriously?
85 mph feels no different with or without.

 

[highdesertranger]

Yes, but are you sitting inside the van during the heat of the day even with the windows cracked, the roof vent open and the vent fan going?

if I am sitting in my vehicle I am driving. if I am parked I am outside. when it's hot I have all 4 of my windows open all the way. highdesertranger

 

[GotSmart]

Noise>>>

If you are using straps to hold down anything, make sure to put a twist in it. Straps that are perfectly flat will always catch the wind and cause a lot of noise. I learned this from an old trucker while toeing a loaded trailer. I tried it and it really works.

As to the difference between this > and this \ , you have to deal with a larger picture of the brick shape of your van. the first shape will hold the wind and create more resistance .

 

[mockturtle]

If you are using straps to hold down anything, make sure to put a twist in it. Straps that are perfectly flat will always catch the wind and cause a lot of noise. I learned this from an old trucker while toeing a loaded trailer. I tried it and it really works.

Yes, it does.  I did that with my kayak straps, too. 

 

[ccbreder]

As the front of the van is like pushing a vertical sheet of plywood down the road, except for the weight, I don't think the flat plywood matters.

 

[Canine]

View attachment 3463our single piece of plywood (ok, maybe 2 cut pieces) with a couple panels shouldn't affect you much, as previous posters indicated.  

Now these loads may:

 

[Canine]

View attachment 3461. Your single piece of plywood (ok, maybe 2 cut pieces) with a couple panels shouldn't affect you much, as previous posters indicated.  

Now these loads may:

 

[Canine]

Ok, I'll stop. Point being, a 1-2 mpg loss, if even that high, isn't that much especially if you are a BLM camper who doesn't move that much... While I wouldn't want the percentage of loss, the actual loss isn't that noticeable.

 

[GotSmart]

After driving across Colorado and Kansas with high winds, the plywood made it hard to go in a straight line. It caught the wind and pushed me sideways. A 3 mpg loss when factored into a 15 mpg vehicle is 20%. If you go 1,000 miles on a trip. that is about 13 gallons, or about $40 to $50.

More than the cost, it is the handling factor. A semi going past the other way on a back road will throw you around. After my last trip. I removed the plywood, and lowered my panels down between the racks.

 

[Canine]

For highway, I agree. I was more thinking of the campers who stay on BLM land for months. Possible alternative for highway drivers could be slats that allow some airflow, with a landscape fabric like Bob uses when he is parked in the desert. It would flap some but the air could pass thru. Maybe?

 

[Mattkcc]

Bob, I'm sure you know this, but for the edification of future readers: This is because:

A) The black material absorbs more of the sunlight, so less ends up striking the vehicle itself.

B) The black material, therefore, gets more hot, which causes the air around it to rise, creating a convection current that draws cool air up from the ground and takes hot air up and away.

Pro Tip: Keep the top of the black shade cloth a few inches away from the vehicle at the top. This lets that column of hot air escape through the gap. If the shade cloth "seals" across the top by laying directly on the top of the vehicle, then it will trap at least some of the hot air against the vehicle with expected results. Yes, this applies even if that shade cloth is mesh. Mesh doesn't let air flow through it freely, as can be observed by just watching it being blown around in the wind.

Your pro tip is right on the money, heat will be trapped if you attach a tarp directly to the van. The same thing happens when people cover there patio's. The best way to rig the tarp is to have it higher and extend over the top of the van. You see most all RV shades attached directly to the vehicle. One way they can get around trapping hot  is to use sun shade material that has a open weave that lets the heat rise through it. Won't keep you dry but will be cooler.