Lifted truck for better aero...?
 

Has anyone thought about, or aero-tested a pick-up truck which has been raised, with tire fairings? My thought, since we cannot lower the vehicle ALL the way to the ground where there would be 0 flow under the truck, if it was raised with a belly pan and rounded front bumper we could allow the air to flow under more freely. The Aptera does this. From the side, picture an aircraft wing. Just a thought...

You expose more tire thus increasing frontal area.

Overall frontal area yes, but if the flow under could be managed better, and fairings for the tires, perhaps the Cd could be lower. Plus the truck could be more useful. I am talking mainly about 4x4 trucks. I was getting ready to start to lower mine with air suspension, so it could be raised for off road use when needed.

Do it and let us know the A-B-A results.
I think it would help on a truck to have a belly pan.
I don't think lifting it will help mpg's.
I think lowering it will.

What kind of truck are you talking about?

I have seen many with an indipendant front susspension that in order to raise it you have to lower the brackets on the front which lowers big blocky components down into the airflow.

edit to add: Look at the components like the t-case, make sure they are all tucked up into the belly as good as possible. A good smooth skid plate will do 2 jobs at once, and it being smooth will help when you do catch it on a rock by sliding easier.

I have a 2003 Tundra 4x4, first 4 tanks I have averaged 19.41 mpg, AZ & NM back roads about 60 % and freeway @70 mph 40%, tires @ 32 psi, they are going to max rated today. There is only about 1 inch to the bump stop, which is about 1/3 of the way from the A-arm pivot to the ball joint, so I can only lower it by about 1 1/2 inches at the most. It has a pretty good "deflector pan" from behind the front bumper down to the suspension crossmember.

I don't know the Tundras very well, most of the people I know while they off-road they prefer the smaller vehicles for the most part.

But anyways, for our part of the country, look at your airflow into the radiator, and the airflow out of the engine compartment. If you improve flow out of the engine compartment and add a patial grill block you might actually improve cooling while improving aero. On my Jeep I vented the hood (it tended to get hot anyways), on my pickup I am looking at venting out the wheel wells.

The Tundra is my personal "daily driver", when I am not with my room mate in her Avalon...26 in town & 29 on the highway @ 75 mph, so I'm not going to "Wheel" the truck very hard core. I have property that is 4 miles of tough dirt road that I'm building on, and being in the concrete business requires me to need a real truck, my Rabbit diesel didn't cut it. Driving my road 5 days a week equals me driving the Baja 1000, twice a year...tough on vehicles! My thought on raising for better aero, is that allowing the air to go under as well as over the truck, it would not be compressing such a "bow wave" so to speak. Not being able to lower the 4x4 much (easily anyway), I'll do what I can with the grill & bumper gaps, and probably electric fans in the near future. I checked the tires today, and 35 psi is their max, so load range E's are in the future. When I can afford the air suspension, I'll be able to test the lower and higher ride height. Originally I was just wondering if anyone had ever wind tunnel tested a truck at different heights. Pics as soon as I can get them small enough.

It's an interesting thought, but as always i think it depends. although lowering is usually seen as a way to improve aerodynamics, i've seen a few indications that sometimes a raised floor will improve aero. for cars like the exclusive bristol fighter it's mentioned it has a high ground clearance for better airflow, and the promissing but sadly vaporised loremo concept also had a relative high ground clearance, creating some sort of tunnel between the thin faired wheels, even the suspention was set up so the center floor could be flat from the front the the back.

all else being equal i think raising the entire floopan can improve airflow underneath and cut down drag, especially when the underbody is flat. however this is on a new design, where raising the floorpan, but leaving everything else in place means less frontal area, if you raise the entire car, wich is pretty much the only option on an existing car, you'll generate more frontal area.

if you know your stock drag coeficient(Cd), and you measure your actual frontal area(A...the surface of a front projection of the car) you could get your actual CdA. now you could make a new frontal projection of how the car would look raised and get a fictional CdA that assumes your Cd stays the same. from this you could calculate how much the Cd would have to drop to a: break even, and b: make an improvement.

from what i've seen on the mercedes website that lists the drag coeficient for every version of a model they make it seems that more high powered versions with wider tires have Cd's that are sometimes 0.03-0.04 higher, that the slipperiest models (most likely the cause of more grill opening and wider tires0).

so this sugest that wider tires not only increase frontal area but also drag coeficient.

tire fairings and smoothing out the underside are always a good thing especially if the vehicle must be raised form practical reasons, however, i don't think raising an existing vehicle can give much improvement.

The problem is when you lift the truck, the rear axle stays at the same height above the ground and is more exposed to the airflow.