Fuel Economy? Topper or Tonneau

[Gray Matter Jeep]

Which would get better fuel economy?
With my topper or with my tonneau cover?

Which be more aerodynamic?

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[Kevin_D]

Studies have shown that a tonneau cover doesn't have a lot of effect on drag, as the airflow over the cab bypasses the bed.
With a cap (topper), I'd think you'd actually generate more drag, due to the vortex created behind the large flat rear surface.
But I'm not an airflow specialist, either.

Kevin

 

[atxatxatx]

If I was to do it again I would have just spent the money on a good topper, so much more useful.

 

[Mr._Bill]

I started with a tonneau cover. I bought a RSI Smartcap with a roof rack when they first became available. Either one is very useful, depending on your needs. Effect on MPG appears to be minimal for either one.

 

[Lost1wing]

I started with a tonneau cover. I bought a RSI Smartcap with a roof rack when they first became available. Either one is very useful, depending on your needs. Effect on MPG appears to be minimal for either one.

I started out with a tonneau cover and switched to a RSI cap. I can't say I have noticed any difference with fuel economy. The cap serves me better than the tonneau cover.

 

[Lost1wing]

Myth Busters had an episode on this topic, well sort of. It was on tonneau covers vs tailgate up vs tailgate down. Things to consider are speed driven and weight. So adding a bed cap you can expect the fuel economy to decrease. Tonneau covers don't add much weight but do not increase mpg"s unless you drive at a specific speed. This may hold true for the vehicle they tested on, but I'm not real sure it will work they way on every pickup.

Tailgate up or down made no difference btw.

 

[Pioneer7]

Topper is likely heavier. I use a cover because I have no use for a topper (yet).

 

[Rahkmalla]

Tailgate up or down made no difference btw.

You must have watched a different episode than I did because Mythbuster concluded tailgate down was the worst for MPGs, which makes perfect sense to me.

Trucks create an air bubble in the bed with air flowing in the reverse direction one would expect not having experienced it firsthand. You can see this yourself if you drive around with a bed full of dried leaves with your rear window open. As you approach a speed where you might expect all the leaves to be scattered by the aerodynamics, they actually start swirling towards your back window. If you've got your back window open, you'll get leaves from the bed flying through the window opening into your truck.

This air bubble effect the tailgate creates acts as a layer for passing air to float over. Allow me to (poorly) illustrate:

With no or an open tailgate, this bubble has difficulty forming and is significantly smaller., causing noticeably more drop-off after the cab for the passing air. Turbulence is bad for airflow and bad airflow means worse MPGs.

 

[Gray Matter Jeep]

A. Driving without a bed cover is not part of the question. I plan to use either my tonneau or topper.

B. Honestly I the deciding factor was my Alu-Cab topper was already on so I left it on.

C. The trip is 3,000 miles out & back.

Thanks for all the feedback.

 

[Lost1wing]

You must have watched a different episode than I did because Mythbuster concluded tailgate down was the worst for MPGs, which makes perfect sense to me.

Trucks create an air bubble in the bed with air flowing in the reverse direction one would expect not having experienced it firsthand. You can see this yourself if you drive around with a bed full of dried leaves with your rear window open. As you approach a speed where you might expect all the leaves to be scattered by the aerodynamics, they actually start swirling towards your back window. If you've got your back window open, you'll get leaves from the bed flying through the window opening into your truck.

This air bubble effect the tailgate creates acts as a layer for passing air to float over. Allow me to (poorly) illustrate:

With no or an open tailgate, this bubble has difficulty forming and is significantly smaller., causing noticeably more drop-off after the cab for the passing air. Turbulence is bad for airflow and bad airflow means worse MPGs.

Same episode I believe. The tailgate up or down was another article and was very much speed and vehicle dependant. Obviously at slower speeds there would be no difference.

Just like winglets on an aircraft. Too fast or too slow and they don't benefit fuel economy. They work best at a specified speed and altitude.

 

[LANGeek]

I started with the roll up tonneau cover then got the RSI Smart Cap.
All theories a side, in practical use or real world use case, I can show no delta in fuel economy.

 

[Geaux Overland]

This is after driving 60 miles average speed ~ 55 mph.
This is in a 3.6L Sport S 3.73 on stock tires with a tonneau cover.

 

[Toyfrog]

This is after driving 60 miles average speed ~ 55 mph.
This is in a 3.6L Sport S 3.73 on stock tires with a tonneau cover.

Didn’t know a Gladiator MPG went up to 30? Mine only gets about half that. ?

 

[ShadowsPapa]

Studies have shown that a tonneau cover doesn't have a lot of effect on drag, as the airflow over the cab bypasses the bed.
With a cap (topper), I'd think you'd actually generate more drag, due to the vortex created behind the large flat rear surface.
But I'm not an airflow specialist, either.

Kevin

It doesn't bypass the bed.
There's a drop in the CD with a cover, how much varies with the bed length, and the type of cover.
Generally the soft cover did better according to GM.

I've posted more recent studies that show a soft tonneau actually cuts drag and has some impact on MPG. Even the Myth Busters were debunked by GM and others.

This is from MotorTrend -

This is a guy who did an independent study - must have been for a college paper or something - (other charts using other trucks shows a worse result for tailgate down (VARIES with truck) and one actually shows a very slight positive result tailgate down. Generally speaking, though, it's worse with tailgate down due to the air behind building pressure and pushing on the truck.

This comes from GM's testing -

 

[ShadowsPapa]

Myth Busters had an episode on this topic, well sort of. It was on tonneau covers vs tailgate up vs tailgate down. Things to consider are speed driven and weight. So adding a bed cap you can expect the fuel economy to decrease. Tonneau covers don't add much weight but do not increase mpg"s unless you drive at a specific speed. This may hold true for the vehicle they tested on, but I'm not real sure it will work they way on every pickup.

Tailgate up or down made no difference btw.

Mythbusters has been proven wrong.
The cap is similar to a tonneau cover.
The tonneau does reduce drag and the impact on drag and thus mpg varies with the cover, the truck, bed length and of course speed but generally over 60 mph you see measurable gains (nothing like 5% or anything that great)

Tailgate down is worse, proven in scientific testing by multiple sources including GM and a guy who did a test on several trucks.

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