i just let my tailgait down same thing really no air is hiting it an holdin back **** i been thinkin of just takein it off less weight

 

http://dieseltruckworld.tenmagazines...e&aid=2835

2nd gen test picture showing flow

http://web.archive.org/web/200304142...er/Tonneau.htm

A Cummins owner who says he ran tests at his university's wind tunnel himself:

http://www.dieseltruckresource.com/d...p;pagenumber=2

Snugtop's test under supervision...that was hindered by the track's restriction that vehicles without roll cages could not go over 45 mph:

http://www.sema.org/main/semaorghome.aspx?id=55785

If you want to run a test yourself
find a steep hill and coast down it
with and without the tonneau.

Want a cheap temporary tonneau to test out the MPG savings?
Buy a $9
'storm window plastic sheet' kit
for a large 3 section sliding glass door
and install it over your pickup's cargo box opening.

 

So hank, explain to me....

A lower drag coefficient means that the vehicle ismore aerodynamic, correct? I would like you to clarify, because from what I see in the stats you just posted, it looks like there was a 14% decrease... I would think this would provide some, even if minimal, benefit.

(here they are in case you did not see them)

Aerodynamic drag changes were:
.43 base

.51 with windows down and tailgate open
.49 windows down tailgate up
.43 windows up tailgate up
.37 windows up tailgate up tonneau on.
.32 windows up tailgate up tonneau on, and underbody sheeting in place.

 

in rough numbers:

a 5.56 mm Nato rifle bullet has a drag corefficient of about 0.17

a baseball has a drag coefficient of about 0.5

a square parachute has a drag coefficient of about 1.00

1994-2001 Ram 4wd is about 0.43 like the link estimates (without rear view mirrors)

2002-2007 Ram 4wd is about 0.528

2008 Toyota Tundra 4wd is about 0.38

2005 Nissan Titan is about 0.44

2008 Chevy Denali SUV is about 0.36

The rough rule of thumb is that a 10% reduction in aero
gives about a 4% improvement in MPG
because wind drag is not the only thing using engine power
...tire rolling resistance and acceleration of the truck's weight
consume energy too.

If the tonneau reduces wind drag by 14%
the MPG of the tonneau equipped pickup
will go up by 14 multiplied times 4/10
or 5.6%

The guys that started the Megasquirt electronic fuel injection volunteer project
put this MPG calculator online
that includes an section on changing the aero changes MPG:

http://www.bgsoflex.com/mpg.html

The square foot area of the front of a Ram is about 35

 

so is the almighty hank saying a tonnaeu cover is a good idea?

 

I think that his point is that a 5.6% increase in economy only really equates to .784 MPG, while still an increase, it is not really noteworthy. Buta 5.6% increase in fuel economy is still something...

 

(that was calculating at 14MPG)

 

Let's see... my Ram drinks a little over $300/month in gas. Sounds like a tonneau could save me a little over $15/mo, assuming at least a 5% increase in fuel efficiency. So theoretically in about two years, an Extang Trifecta ($328 with shipping was best I could find right now) would pay for itself. I'm choosing a soft tonneau since it's lighter and less expensive and frankly, I'm cheap-assed. Soon as I get my tax refund...

 

I put a soft roll up on mine and am on my first tank so I'll check it soon. Can't remember the brand but it was $500 from store but I know the distributor so I got it straight from him for 250. I figured the weight of a hard top would negate any gains but a soft may get some on the highway.

 

If someone were to build a tonneau shaped to improve aero on the Ram
to the maximum there might be a bit more MPG gain.

A tonneau that was higher at the rear window end
that near the tailgate
would be better
but it would not be so high to block the rearward view.

Someone with body shop experience (or boat shop experience)
who is good with fiberglass or plastic molding
might be able to start a home business
supplying Ram owners with an special design tonneau,
perhaps called
Opti-Aero
MaxMileage
SleekSloper
etc