KennyL

I found this for those that want better mileage.


Do Tonneau Covers Really Improve Gas Mileage?
Truck owners often have their own theories on how to improve gas mileage and reduce the air drag on their pickup trucks. One simple solution is to lower the tailgate. Another is to replace the tailgate with a cargo net. Bed caps or tonneau covers can be added as well. According to the Federal Chamber of Automotive Industries, while sales of passenger vehicles in July 2004 were down 9.2% vs. July 2003, sales of SUVs and light trucks increased 1.2% and 4.2%, respectively. With the desire to own pickup trucks combined with high gas prices, it seems as though more studies on how to decrease drag should be conducted.

In the simplest terms, drag deals with resistance to airflow. Cars and trucks alike experience drag. The drag coefficient, Cd, is usually determined experimentally—the lower the value of Cd, the better. The most important thing for the average car or truck owner to know is that the larger the value of Cd, the more work the automobile has to do to push against the air it drives through. And if the car or truck has to do more work, it is going to use more fuel.

Two students from Western New England College’s Department of Mechanical Engineering, Todd J. Ortolani and Vanwijak (Kehm) Ewosakul, wrote a paper in 1997 entitled "Improving Aerodynamic Characteristics of a Dodge Ram Pickup Truck." Their paper describes a series of experiments in which various conditions were simulated in a water tunnel, while making use of different aftermarket products, in order to determine the coefficient of drag for each condition.

The coefficient of drag of the pickup without its mirrors was 0.432—this is the baseline value in order to compare other conditions. Notice that when a square cap was added, Cd had a value of 0.480, representing an 11.11% increase in the coefficient of drag. Surprisingly, there was a decrease in the drag coefficient when the tailgate was lowered, with a value of 0.414, even though the drag coefficient experienced an increase when the tailgate was completely removed. Cd was reduced by 11.81% with a value of 0.381, when a tonneau cover was added to the truck. And finally, the best result were produced from a cap Ortolani and Ewosakul designed—the drag was reduced by 30%, with Cd equal to 0.302.



Condition Drag Coefficient, Cd % Change From Baseline MPG
Baseline 0.432 N/A 16
Square Cap 0.480 11.11% 14.9
Cargo Net 0.461 6.71% 15.33
Removed Tailgate 0.447 3.47% 15.65
Lowered Tailgate 0.414 -4.17% 16.42
Tonneau Cover 0.381 -11.81% 17.18
New Cap Design 0.302 -30.09% 19
Source: Improving Aerodynamic Characteristics of a Dodge Ram Pickup Truck

In order to determine how coefficient of drag translates into fuel efficiency (MPG), a simple equation is derived. First, assume the Dodge truck is equipped with the 5.2 liter V8, combined with an automatic transmission. If the truck is 2WD, an average 16 mpg fuel economy is assumed. Under this condition, the increases and decreases in drag can be equated to fuel consumption using a simple equation. We will call Y the baseline mpg, which is 16. X will represent the ratio of the change in mpg (A) to the change in drag (B). Z will represent the percentage change from the baseline condition to a new condition, where a decrease in drag is a positive (%) and an increase in drag is a negative (%). In each case, A is what needs to be determined, and it can be found by: A = ( X x Z ) + Y. The results in the table above show the gas mileage results using this equation.

The study indicates that the best way to reduce drag, and thereby improve fuel efficiency for pickup trucks, is to add a tonneau cover, unless an improved cap design is developed. However, studies have indicated that other factors can also contribute to improved fuel efficiency, including choices in air filters, aftermarket grilles and by keeping tires properly inflated. Also, it is important to remember that drag depends on the size and shape of the vehicle, and therefore a Chevrolet, a Dodge, and a Ford pickup with the same cap might have different drag coefficients because of different design features. While the increases or decreases in drag coefficients might not mean much to most truck owners, increases or decreases in fuel economy have both economical as well as environmental significance.

KUMMINZ1983

I avg. 13 mpg around town. This sucks. Is this normal?

tex04

I am gettin anywhere from 15-18 and i have a 2000 4x4 dually which has the ats tranny and is 4x4.

high country

One thing to consider in your cd=fuel/economyX3.1423 if you drive without a tail gate you have no strength in the rear of the bed thus over time you are buying a new box because you wanted to save .00023 per mile.

I just hate to be behind the guy whose box is flapping like a flag
GREG

smokindog

Before mods I could pull 24mpg at 60mph, but lately I can't resist smoking anything so economy has gone out the pipes.

Mopar1973man

On the driver side rear of the intake manifold. The MAP sensor is there too. It will take a 13/16 socket (i think) to remove it. Either Phox Mulder or Dr. Evil has a picture of where it located.

I currently looking into doing any kind of mod that would help fuel mileage. Being that diesel fuel hit $2.859 it getting hard to do my job. (Traveling computer tech).

I think now that I did the muffler delete I might be closing in on getting 21 or 22 MPG... It will also help dumping some of my stuff out of the bed...

montemorris

We bought our 2001 HO, long bed, 6 speed manual, 3:55 rear end, last April and during August drove it 5400 miles Missouri to Oregon round trip. The first part of the trip we were towing my son's Cavalier on a tow dolly and averaged 16.5MPG. On the way back we averaged 21.5MPG with the tow dolly empty, but loaded in the bed and the tongue sticking straight up in the air. We routinely average around 20 MPG on each tank with most of it highway miles but maybe 1/5 around town. The truck is stock, I believe.

NV BLU

I have an 03 2500 quadcab shortbox. It is the HO but basically stock out of the box. I get between 20-22 mpg if I keep it below 2000 rpm. After that, it goes to hell in a handbasket. I tow a 10,000 lb. 5th wheel and if I'm ***** to the wall, I get around 10. Towing conservatively, I can manage 11 or 12. For the two miles per gallon; get outta my way!

d110077

4.10 is killing me, cruising around town get about 13.9 most the time. AIT sensor clean I just check, just bought the truck I think the dealer change new oil, filter because they look new. Stock truck and that is the best I got. After my tire worn out I going to get the biggest tire I can find to balance the gear.

dssimecek

Yup, not overjoyed with my 13.8 mpg with fuel @2.699 /gal, at least it is not lonly down here. I am going to to about a 100 mile round trip on Monday. If I can remember I will do theold manual MPG calulaation. Don't think oh overhead computer is that accurite, it is accurong.

Red3quarter

Driving around town i usually get 15 mpg and on the hwy if i don't keep my foot out of it (85 mph) i get about 17.5 - 18 but if i do keep it around 70 mph i have seen 20 mpg. And my truck has 4.10's, 4x4 and a auto tranny. I usually run some Power Service in each tank, i find that it helps my fuel mileage.
matt

darrenG

so far, w/ 1 tank on my truck under my belt, I got 16.4 city. Hopin' to see that go up but it beats my jeep by 1-2 mpg.

P.J

I've gotten better mileage over the past two weeks, Bone stock (for a few more weeks). Looking at 19.2-19.4 on the overhead,(NON Highway) don't know how accurate, but the fill ups are getting further apart? Must be the weather and summer fuel blend?

Haulin_in_Dixie

My mileage is much better in very warm temperatures, more than it should be, and on the same fuel. I would like to find out why that is. Will be changing the two sensors to see if that is it. Its a diffeent engine below 50 degrees at night.

johnh

you cannot compare a dually mileage with a 4 x4. i know , i had a dually and i got around 16 mpg at 70 mph