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.

Very true, but since I will have to get better tires, that will take a higher pressure, I can go taller also. This will fill in the wheel well better and give me an effective higher gear ratio. Not much can be done with the axle unless I went with IRS, say from a Hummer H-1. Thats too much reconstruction for this truck.

LR-E tires simply for higher pressures is not the way to go. Stick with the load range specified by the manufacturer. A better quality tire would be my choice, of the optimum tread design. On the oilfield runs I've made -- down long caliche lease roads [paved with rocks the size of softballs sometimes] -- I don't see either the necessity of 4WD or lug tread tires. There is a compromise in there that is a better choice, IMO. Stock height and stock tire/wheel size. Slow down is the other answer.

You will want to be carefull as to what type/quality of tire you run on rough roads. I have actually had tires break in fassions similar to a rock cracking a window.

raising
 

If you can gain access to one of Hucho's books,he's got some data on ground-effect,and the relationship between ground proximity and drag coefficient.
With a pickup,your going to be in a dark zone,data wise,as very little is done in wind tunnels with respect to off road vehicles.
*Raising the truck will degrade its fineness-ratio ( length/height) and typically this will increase drag.( strike - 1 )
*as mentioned,your adding frontal area ( strike- 2)
*in low drag vehicles,even with full belly pans,active suspension is used to lower the vehicle at speed to lower frontal area and Cd. ( strike-3 )
* in low drag vehicles,in addition to lowering,an active airdam is lowered to block off as much air from beneath the vehicle as possible. ( strike-4 )
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*Western Washington University's Viking series of cars used a 'raised' floor with inverted airfoil section.These cars did not demonstrate remarkably low drag. ( strike - 5 )
* Raising the truck raises the center-of-gravity and can seriously affect stability ( roll-over ) (strike-6 )[ If your not killed outright,you may be spending the rest of your life in a wheelchair].
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We have a raised Toyota pickup out here where I live.It can no longer negotiate an uphill grade without losing speed and forcing a downshift,something that was not an issue at the lower height.
* to mitigate this we're planning a full-depth wrap-around airdam,as low as the lowest suspension member.
* grille-block
* the original truck cap will be re-installed
* fairings for the tire faces are planned
* maybe trailing fairings for the tires as well
* probably no belly pan 'til we see what the other mods do.
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I would recommend that you leave the height as is and go after your other mods.Safety first!;)

Thanks for the info. I have a seasonal creek to cross at times, steep hill with some snow in the winter, and a short very steep hill on my driveway that requires 4 wheel drive or a little run. I prefer slow and no tire spin. Plus I do some prospecting out in the desert, so lots of rocks. The only tires I buy are BFG All Terrains. On my 97 Cherokee I went from 16 & 22 psi F/R (perfect tread wear and footprint) to 40 & 45. Harsher ride but not bad, wear towards center some, and almost 2 mpg increase.

I was reading somewhere on here there was a mention of, "in some cases" raising can be of benefit. It was in a looong series, and I believe it had the streamlining of a van in French. If frontal area is the measurement of the area of vehicle parts moving through the air as seen from the front, then the height above the ground should not matter except for what ever "extra" parts see the air excluding the ground effect. It "IS" a truck which gets used off road, so I can't "slam it", and by raising, I'm talking 1-2 inches, not the stupid "How high can I go" BS. I have found some load range "D" tires which are about 1 1/2 inches larger dia., that will help the gearing some too. They are rated to 65 psi, so 45-50 would be good I think. No wheelchairs here, I've got 40+ years of 4-wheeling, and have only rolled once (off road race long ago)! But thanks for the concern! Your Toy was probably a 4 cyl with 33 inch or larger tires, they don't like those without major gearing changes. I have no power problem, 4.7L. I-force, V-8, so It'll pull 33 inch tires easily. Plus with the higher load rated tires, they get taller without getting a lot wider. I'm not looking for "The look".

Never heard of a truck getting better gas mileage from taller tires. I think the combination of bad aerodynamics and higher weight vs cars leaves you with very little headroom for taller "gearing".


My Cherokee has a 2" lift, a front skid plate that directs air down, and 31" tires (stock are 28"), and I only get 16mpg.

I am not trying to build a higher mileage vehicle than a car, just trying to improve what I have to drive now. Trucks being bad to start with, leave a lot of room for improvement, and there are a LOT of them out there. if the truck is geared low 3.73 or 4.10, then any way to get the rpm's lower would be an improvement, depending on engine type and it's torque curve. Years ago, I had a 72 Blazer 4x4 with a low compression 350 and 3.07 gears. I put a 10.25 cr 396 big block in it and with 32 inch tires got almost 18 mpg. The engine was only turning about 2000 at 60 mph. My Cherokee had no lift, 9.50 x 30 tires, 4.0 motor, and automatic.

Im guessing the XO's, good all round tire, friend of mine have been using those for years. One would run his at 60 psi on his Cherokee and he could get 24mpg on a good day. thats with a 2 inch lift and 31 inch tires, and an automatic.

Many people over state the possibility of rolling over, thinking if you sneeze you will wind up upside down in a ditch.

You might look at getting a truss for the rear axle, it might help with the airflow arround it. The right ones can strenghten the axle as well.

Those are the tires, I've had great luck with them. My Cherokee had about 60,000 miles on a set, they never even needed rotation.

1-2 inches
 

A couple inches will expose a slice of tire on each side and maybe a bit more of the naughty bits underneath,so it doesn't sound like a monumental departure from where you're at.
Your daily requirements will dictate your needs,and it sounds like the clearance would be welcome.
I hope that's not fast-moving water that you've got to go through.
If you can post a few views of the truck it would give us something to 'think' about.
And yes,the p'up out here is a Toy,with the 22 or 24-R.Don't recall.I think it's 31-inch tires on that one.It will have similar needs.

Here are some photos...maybe?/Users/robertgay/Desktop/IMG_0948.JPG
/Users/robertgay/Desktop/IMG_0949.JPG
/Users/robertgay/Desktop/IMG_0951.JPG

OK, That didn't work,maybe this...
That might have done it...Sorry to all, I'm MAC learning!

The oil drip is Jeep oil.

I'll second what others have said, unless you have a way of controlling turbulent flow under the truck body you are better off cutting off the flow with a massive chin spoiler of some type.

I did this very thing with my 4x4 S-10 and saved 3 mph on the highway. Simple as screwing a 6 inch garden plastic trim piece to the bottom of the existing valance.

I'll post photos of the project soon......EDIT, I now have +5 posts!

Link:
http://forums.pelicanparts.com/off-t...effective.html
http://i184.photobucket.com/albums/x...%20Up/SP11.jpg
http://i184.photobucket.com/albums/x...k%20Up/SP7.jpg
http://i184.photobucket.com/albums/x...20Up/CHIN7.jpg

On every vehicle enthusiast forum out there this thread would have died quickly, not simply to lack of information. Instead, here, it has improved considerably. The parameters of what is desired are now more clear, and some numbers to work against are coming to light (even if dimly).

That is very cool! It even looks factory. That is sure to be on my soon to do list.

Thanks Much!

Jeeps do have a tendency to mark their teritory.