Does a traditional square pickup camper shell topper help or hurt drag & mileage?

[John Topper]

Myth busters did do an episode of tailgate up or down.

Just do a google search and you'll find the link to it.

[ECONORAM]

Originally Posted by MetroMPG

Colour me surprised. I heard back from the company whose "documented tests" I referred to in post 14. The results were posted on the vendor's site after all. (In my defense, it would have been useful if the page I originally found that mentioned the tests had a hyperlink to the relevant page!)

Have a read - their experiment is documented here. Their test methodology beats the heck out of Pop Mech's. But it still could have been improved - easily.

They did A-B testing of a cab-high cap vs. open bed on a 2004 Dodge Ram 1500 SLT Quad Cab with a 5.7L Hemi V8. They used a closed course, and cruise control at 45 mph for 50 miles of each condition.

Here's an example of their cab-high cap:



Their claims:

19.38 mpg (US) - cap on
18.06 mpg (US) - cap off

... suggesting a 7.3% increase in MPG with the cap.

(They also document testing two tonneaus on two other trucks.)

The two most obvious pitfalls to their testing were:

1) it wasn't A-B-A, and,

2) they relied on the AAA's official "3-click" method of filling of the tank to determine fuel use (I don't care whose filling methods they were following to the letter, that approach still opens things up to potentially significant errors).

EDIT: the other important omission from the test is that it doesn't say whether the cap is better or worse than a tonneau.

I realize this thread isn't brand new, but I'm disappointed they did their testing at 45 mph. Really? They should consider their customer base. How many do they really expect to drive 45 mph down the highway? I suspect they chose 45mph because much above that the drag really starts climbing...at least on my pickup it does.

Originally Posted by Christ

I agree.

I find it difficult to quantify improvements for a specific truck against other trucks without some context, because each model has varying cab height, bed length, etc.

What specifically works for one truck may be totally off for another. The only concrete point is that they all are affected by the same rules, but the workarounds are often different to a degree.

Good point. If (if) I can find a way to easily remove my topper without destroying it, I'll try to do some A-B-A tests for my RAM. I am curious to see how close it'd be to the 1994 Ford results. Or maybe some A-B-C-B-A tests with C being a bed cover config...

Originally Posted by aerohead

I dug through the rat's nest looking for square bedcover-related material.
I found two articles which may share some insight and one personal experience to share.
(1) When the all-new Chevy/GMC pickups entered the market around 1987,their Cd had been trimmed from 0.535,to 0.45.
In 1992,the Chevy Suburban K 1500 was reported with Cd 0.39,about 11% drag reduction.It's station wagon style roofline closely mimics a traditional square camper shell.
(2) When the VW Vanagon loses it's roof to become the drop-side pickup truck,it's Cd grows from 0.42,to 0.46 ( about 8.5% difference)and with identical power,the top speed falls from 83 to 78 mph.
(3) When John Gilkison owned the T-100 which I now have,on astronomy camping trips,a LEAR square type fiberglass shell was reported to increase fuel economy by up to 1.2-mpg,a 4.8% mpg improvement,and 8% drag reduction.

Interesting data on the GMC Cds. I'm a little surprised at the T-100 results.

[crashnzuk]

Hey all, I'm new here but have been reading what I can about pick-ups. Has anyone checked economy while towing a trailer, shell vs open bed? I am making a trip to Idaho from California next week and will be towing my open car trailer with my '91 Dodge W250 4x4 reg cab long bed diesel pick-up. The truck is stock height (tallish) with an older Warn brand winch/bumper combo up front that I have fitted with an air dam that hangs 12" below the bumper with the bottom edge about 13" off the ground (even with the front axle centerline).

On the way up I will have an AMC Eagle wagon on the trailer and on the way back I will have a '71 Dodge D100 2wd flatbed on it. I would think that having a shell on the back would direct the air over/around the trailered vehicle better vs an open bed, do you guys think this is a fair assessment?

I can borrow a shell from a friend that has the same truck as mine to make the trip. I ran this same combo (air dam and shell) in the spring to Idaho and back, but wasn't towing anything and had a couple tanks with my best MPG to date, so I think it has merit. Just wondering what your thoughts are about hooking an open car trailer up behind it with the vehicles mentioned.

Thoughts?

Travis..

[aerohead]

Originally Posted by crashnzuk

Hey all, I'm new here but have been reading what I can about pick-ups. Has anyone checked economy while towing a trailer, shell vs open bed? I am making a trip to Idaho from California next week and will be towing my open car trailer with my '91 Dodge W250 4x4 reg cab long bed diesel pick-up. The truck is stock height (tallish) with an older Warn brand winch/bumper combo up front that I have fitted with an air dam that hangs 12" below the bumper with the bottom edge about 13" off the ground (even with the front axle centerline).

On the way up I will have an AMC Eagle wagon on the trailer and on the way back I will have a '71 Dodge D100 2wd flatbed on it. I would think that having a shell on the back would direct the air over/around the trailered vehicle better vs an open bed, do you guys think this is a fair assessment?

I can borrow a shell from a friend that has the same truck as mine to make the trip. I ran this same combo (air dam and shell) in the spring to Idaho and back, but wasn't towing anything and had a couple tanks with my best MPG to date, so I think it has merit. Just wondering what your thoughts are about hooking an open car trailer up behind it with the vehicles mentioned.

Thoughts?

Travis..

I would absolutely borrow the shell for the trip.

[KamperBob]

Originally Posted by crashnzuk

Hey all, I'm new here but have been reading what I can about pick-ups. Has anyone checked economy while towing a trailer, shell vs open bed? I am making a trip to Idaho from California next week and will be towing my open car trailer with my '91 Dodge W250 4x4 reg cab long bed diesel pick-up. The truck is stock height (tallish) with an older Warn brand winch/bumper combo up front that I have fitted with an air dam that hangs 12" below the bumper with the bottom edge about 13" off the ground (even with the front axle centerline).

On the way up I will have an AMC Eagle wagon on the trailer and on the way back I will have a '71 Dodge D100 2wd flatbed on it. I would think that having a shell on the back would direct the air over/around the trailered vehicle better vs an open bed, do you guys think this is a fair assessment?

I can borrow a shell from a friend that has the same truck as mine to make the trip. I ran this same combo (air dam and shell) in the spring to Idaho and back, but wasn't towing anything and had a couple tanks with my best MPG to date, so I think it has merit. Just wondering what your thoughts are about hooking an open car trailer up behind it with the vehicles mentioned.

Thoughts?

Travis..

Food for thought: I'd at least consider putting the wagon on the trailer backwards for leg 1 of the trip. It shouldn't take long to test load both ways. Take pix and compare with Phil's template. Whichever better stuffs the wake I tow that way. For the return leg since you said flat bed my guess is the truck should face forward. Regardless, fold mirrors as flat as possible, etc.

Safe travel!

[crashnzuk]

Good idea on the wagon backwards, I hadn't considered that. Typically I can't load anything backward due to weight distribution of the vehicle causing a lack of tongue weight. Being a wagon, the rear might be heavy enough to be able to balance it out. I'll have to give that a shot. The mirrors are fixed, non-folding, so they will be what they are. Good input The truck on the other hand will only fit and balance facing forward due to trailer size, weight dist, etc, so that will just have to be. I know flat beds have terrible aero.
Travis..

[ECONORAM]

Originally Posted by crashnzuk

Good idea on the wagon backwards, I hadn't considered that. Typically I can't load anything backward due to weight distribution of the vehicle causing a lack of tongue weight. Being a wagon, the rear might be heavy enough to be able to balance it out. I'll have to give that a shot. The mirrors are fixed, non-folding, so they will be what they are. Good input The truck on the other hand will only fit and balance facing forward due to trailer size, weight dist, etc, so that will just have to be. I know flat beds have terrible aero.
Travis..

Non-folding mirrors on the towed vehicle? Nothing a roll of duct tape can't smooth out...
Safe travels to you.

[crashnzuk]

If I load it backwards, the mirrors will be pretty far back and facing the wrong way so they would be pretty serious air scoops I think. Since the mirrors on the wagon are fixed, what would you all think about splitting a nerf football and taping it around the mirrors? It would just look like a pair of footballs affixed to the doors, sound goofy?Travis..

[crashnzuk]

Well, I made my trip so I thought I'd let you all know how it went. On the way to Idaho, I loaded the Eagle wagon on the trailer backwards. I had to move it nearly all the way forward to make it balance, so this made the gap between the back of the truck and wagon as small as possible. Traveling a steady 70mph, even holding speed up the long grades, my mpgs were 14.2, 14.4, 14.6, and 15.6 (last fill had about 25 miles without trailer). On the way back, I loaded my 71 Dodge d100 forward and hit the road. I also held 70 mph, but this truck was heavier and had worse aero. The mpgs were 13.0, 14.2, and 14.6. I haven't filled the truck since getting home. This was with the camper shell and my home made air dam that I previously mentioned. I can take and post a couple pics if anyone is interested in seeing.
Travis..

[Sven7]

Very interested in pics to see how well it filled the wake. Also, I like your taste in cars. So pics of those too if you could

ECONORAM- My dad's car has a trip computer and the average speed over trips is usually in the range of 40-50mph. I suppose it's not the most scientific way to test it, but you'd have to have a pretty long commute to bring that average up to 60mph or so.