Truck Cap Aerodynamics: Wedge vs Standard

ThundahBeagle

Well-known member
View attachment 753359
FWIW, there are 2 horizontal AL bars on the front of the camper ladder rack, all of the bugs are on the top bar.The bug splatter was about the same pre and post roof rack. I suspect I could have gone with a higher camper and not optioned the lower front.
The bugs are on the tob bar, I am guessing, because you have a roof basket preventing any getting on the slope of the cap?
 

ThundahBeagle

Well-known member
Also, is this shell aluminum or fiberglass? I wager, if you want it because it is stronger than normal fiberglass, and if you intend on putting a rack or basket full of stuff up there, that stuff will cause a bigger hit on fuel economy than the slope or not?
 

SDDiver5

Expedition Leader
Regardless of the drag, wouldn't the weight of said cap, weight of bed cargo and driving style and driving terrain make more of a difference? If you're stop and go in a suburban area it will suffer more than being on a flat desert road at a constant speed?

I'm no engineer...just uneducated thinking outloud.
 

olshaggy

Member
The bugs are on the tob bar, I am guessing, because you have a roof basket preventing any getting on the slope of the cap?
He said, "the bug splatter was about the same pre and post roof rack" (as opposed to the ladder rack), so the basket doesn't explain it.

Also, is this shell aluminum or fiberglass? I wager, if you want it because it is stronger than normal fiberglass, and if you intend on putting a rack or basket full of stuff up there, that stuff will cause a bigger hit on fuel economy than the slope or not?
I'm planning to get an aluminum shell, though not because of its strength. Yes, anything we put on our racks definitely increases drag, but as I said in the original post, I'd like to hold constant (i.e., control) all the other variables in order to focus on how cap shape affects drag.
 

olshaggy

Member
Regardless of the drag, wouldn't the weight of said cap, weight of bed cargo and driving style and driving terrain make more of a difference? If you're stop and go in a suburban area it will suffer more than being on a flat desert road at a constant speed?
Quoting myself from the original post: "I'm well aware that there are a lot of other variables (speed, weight, racks, etc.) at play when considering gas mileage, but let's assume all of those are held constant for this comparison."

That said, agreed that the difference in weight between any two caps is relevant, but we're probably only talking about a few percentage points difference in this case so it's nearly negligible.
 

chet6.7

Explorer
Oh that's interesting @chet6.7! If I'm understanding you correctly, you're concluding based on the bug splatter pattern that regardless of the roof rack, the shape of the cab is driving most of the air up toward the highest point of your ladder rack, in which case it may not have made much of a difference in aerodynamics whether you had a 26"-32" wedge (what I'm guessing I'm looking at) or one that started at 32" high. Is that right?
Yes, and yes 26-32 inches.
The rack had been on for some time when that picture was taken,if you blow the picture up you can see the distribution of bugs that fly no more.
 

llamalander

Active member
Do you plan to store things on the cab? can you use that space to make a surface to bridge the top of the windshield and the back of a full height box?
In my experience, I start taking a noticeable hit to my MPG over 60, because my truck is shaped like a brick, but my high-speed milage improved once I got a shell compared to an empty bed.
I tend to think aerodynamics are more pronounced at highway speeds and pretty irrelevant below them.
 

olshaggy

Member
Yeah, definitely primarily an issue at highway speeds. I have thought about putting a rack of some sort on the cab that would also function like a wind deflector, but not only can I not find anything wedge shaped, I haven't been able to find a roof rack / basket that would work on a regular cab at all. Curious if anyone knows of one that would fit, or failing that, of shops that might fabricate something.
 

billiebob

Well-known member
Back when GMC made the Syclone and that opened the high performance thing to trucks.... someone... Car & Driver or whoever did a thing on aerodynamic truck box... covers/things.

Full, sleeper, tonneau. half, no tailgate vs.....

The best was a tonneau over just the rear third, leave the front open....

Likely not applicable here but food fer thought.

Incidentally, the Syclone and Typhoon with the Buick Grand National V6 and AWD both had better 0-60 times than the Corvette of the same year.

cfs-1991-gmc-syclone.jpg
 

olshaggy

Member
Turns out there's an active discussion of this same topic over at Tacoma World, where a member has done some computer modeling of various cap shapes. As @Buddha. suggested with the aerocap link, shape of the front of the topper seems to have much less impact on drag than the shape of the back. They're designing these things backwards.
 

rruff

Explorer
shape of the front of the topper seems to have much less impact on drag than the shape of the back.
Been known since flying things were first made, but styling tends to trump fuel consumption... and there are practical aspects too, like volume and ease of use. Thanks for the link... I'm tempted to join just to get in on it.

Round the corners on the leading edges; a radius of a few inches will help a lot. Also note the front spoiler effect; it throws the air up at such a sharp angle that it completely detaches from the roof, which is the opposite of what you want. That's a tricky area. Tapering in the rear is good because it reduces the area and wake where the air just gets dumped, but you also lose some space or have an extra "thing" hanging off the back.
 

olshaggy

Member
Yeah, kept it general intending to make the thread relevant to a wider group of folks, but this would be for a 2016 Toyota Tundra regular cab long bed 4x4. I expect to be living out of it most of the year, occasionally in urban areas but mostly on BLM and forest service land out west. I'm almost 6'3", hence the desire for the high cap.
 

Mickey Bitsko

Adventurer
You mentioned your concern with gas mileage, imo, you would be sacrificing a huge amount of comfort for the sake of a few extra bucks for fuel.
Unless, your lifestyle requires a good deal of driving. You'd probably better off with a half cabover so to speak, wouldn't be as light but much more storage full timing.
 

olshaggy

Member
Don't need that much space, and want to keep this build as light and low as I can reasonably manage to maximize the places the truck will be able to go. I'll spend most of my time outside the truck, just want to be able to sit up straight sometimes.
 

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