Does a tonneau cover help with gas mileage?

I have to wonder if having a 5ft bed makes a difference because when I have my tailgate down and kayak in the back I get better mileage.
Or maybe it's that the kayak in the back changes the aerodynamics.

 

This thread has been a good read, love that mythbusters did an episode on it.

 

I have a Diamondback, and that is a no.

 

Not a very good test, drag becomes much higher at speeds above 55 mph. Scientific tests show bed covers do reduce drag at higher speeds.
https://www.agricover.com/downloads/pdf/2007_windtunnel.pdf

https://tundraheadquarters.com/the-tonneau-cover-fuel-economy-myth/
Does a good designed bed cover increase mpg? Yep. But not by much.

 

One thing they are great for... Keeping stuff in the bed dry and out of sight. I've put them on many trucks I have owned over the years and not once noticed an increase in MPG

 

Means nothing since so many variables affecting mpg you would never notice a tenth or a few tenths mpg gain or loss of a tonneau cover without rigorous controlled scientific testing.

I doubt anyone buys a tonneau cover expecting noticeable mpg gains, I sure didn’t.

 

They're great for keeping stuff out of sight and dry. That's about it.

 

thats literally all I had mine for haha was annoying when you need to move something in the rain and cant keep it dry

 

If that's what your spouse needs to hear to allow you to buy one, then yes, it makes a HUGE difference.
In reality, no.