truck cap aero

[craveman85]

Fall/winter kind of force me to use a truck cap. I currently have a lightweight aluminum cap that has ladder racks on top built into the framework. I lose 3-4 mpg with it on. If I were to switch to a high rise fiberglass cap would it help mpg over the aluminum? I'd like one that slopes up to about a foot higher than the cab at the rear. these are usually smooth slopes where as my ladder rack sticks 2" above the cab and is a vertical flat surface. Well actually 2,a front and a rear.

[freebeard]

Are you familiar with the term 'aerocap/aeroshell'? If not, put it in the Search box in the upper left.

Your present cap suffers because of the square cross-section of the cross bars and interference drag between the cross bars and the top. The high rise cap goes in the wrong direction, increasing the size of the hole the vehicle punches in the air.

It's hard to say which would be worse, but they won't be better.


Comprehensive list of aerodynamic pickup caps/aeroshells on EcoModder (& elsewhere)


See a trend here?

[craveman85]

Yeah I'm familiar with the aerocaps but this time of year involves lots of gear being stowed back there like my ice fishing stuff and also I sleep back there on hunting trips which wouldn'tbe so great with an aero cap. Just trying to decide the lesser of 2 evils. I feel I'd have more use of a high rise cap over a standard fiberglass cap.

[aardvarcus]

Most aluminum caps have sharp square corners front and back, and don't really "fit" the shape of the vehicle very well. A cab height fiberglass cap which matches the truck's bodywork can actually improve MPG highway. If you have to have a ladder rack, I would either try to get a low profile aerodynamically shaped ladder rack, or get an easily removable one.

An extra height fiberglass cap probably won't be that different than a cab height aluminum one. One has worse CD, the other has more frontal area. Adding a ladder rack to that won't help either.

So basically, aeroshell is best. If you could at all utilize a cab height shell, I would try to make that work. If you don't need the extra capacity every day, but only on occasion, you might even consider getting a small trailer.

[freebeard]

Now we have a use case*. The next question would be 'Make or buy'. The Wholey Grail is a pop-up aerocap. It's been tried but I don't know of any great success. Pickup beds come in long/short and wide/narrow. Which is yours?

If the need is for cargo volume, rather than the rear opening height, go for a cab-height cap that is long enough to fill the lowered tail-gate—like a slide-in camper.

*This cries out for an ice-fishing hut that is trailerable. I designed one in college that was a corrugated metal oval that stood on it's tail in use with the hitch in the air. Do you require a picture?

[aerohead]

Originally Posted by craveman85

Yeah I'm familiar with the aerocaps but this time of year involves lots of gear being stowed back there like my ice fishing stuff and also I sleep back there on hunting trips which wouldn'tbe so great with an aero cap. Just trying to decide the lesser of 2 evils. I feel I'd have more use of a high rise cap over a standard fiberglass cap.

bondo's 'Aerolid' provides a lift hatch with built-in tent.When parked,it has the headroom of a conventional cap,then 'aero ' for the open road.Really worth checking out!

[Sven7]

As others said, both options will likely be equally bad. One of the big problems is the ladder rack. I wonder if you could build brackets to mount the ladder underneath the truck and hide it behind a big air dam. If you could slot it into the front bumper and secure it up in back it might sit snugly and not be any more inconvenient than throwing it on the roof. You'd have to do some testing to make sure it doesn't interfere with the axle, driveshaft, etc.

[BamZipPow]

I guess you could build an aero enclosure fer the ladder on top of the aero cap. I don't that's been done yet.

[redneck]

freebeard

*This cries out for an ice-fishing hut that is trailerable. I designed one in college that was a corrugated metal oval that stood on it's tail in use with the hitch in the air. Do you require a picture?

Yes...

>

[bondo]

Originally Posted by aerohead

bondo's 'Aerolid' provides a lift hatch with built-in tent.When parked,it has the headroom of a conventional cap,then 'aero ' for the open road.Really worth checking out!

You can raise it up when you are parked to camp in or whatever. You can also leave it raised up and drive at sustained freeway speeds all day long. Gas mileage suffers but if you have a lot of cargo to haul you can.