Lifted truck for better aero...?

[CFECO]

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.

[slowmover]

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.

[TheEnemy]

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.

[aerohead]

Originally Posted by CFECO

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...

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 )
-------------------------------------------------------------------------
*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].
--------------------------------------------------------------------------
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.
--------------------------------------------------------------------------
I would recommend that you leave the height as is and go after your other mods.Safety first!

[CFECO]

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.

[CFECO]

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".

[winkosmosis]

Originally Posted by CFECO

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.

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.

[CFECO]

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.

[TheEnemy]

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.

[CFECO]

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.