That's what the original argument was, but the study by the ME student says otherwise. He says it's better with the tailgate down, rather than the tailgate up.

You guys may not like me anymore after reading this post (maybe you don't like me anyway)...but I've always thought people who drive their trucks with the tailgate down (for no other obvious reason) are complete idiots. I laugh everytime I see it. And you ALWAYS see some dumb*ss whose tailgate has a phone pole dent in the top of it where he backed it into one while the tailgate was down...in an effort to gain 20 more miles to a tank. LMFAO!!! Folks...its just DUMB. I've owned a pickup since I was about 17 and I have driven them hundreds of thousands of miles and I'm quite certain that under AVERAGE driving conditions there is NO benefit from leaving your tailgate down. Well...maybe one....if your bedliner isn't secured and you don't really like it, it may blow out easier when the tailgate's down. <img src="/forums/images/graemlins/lol.gif" alt="" />

By the way...since we're on the subject, here's an interesting fact: Did you KNOW that a 60's vintage VW BUS has a lower drag coefficient than the stingray bodied corvettes have? FACT. Think about that one for awhile.

my cousin runs an 85 chevy pickup at the local drags..we have the time slips to prove that just with removing the tail gate it made almost 1.1 seconds faster time...but thats down here in lousyana..the air is thicker... <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/lol.gif" alt="" />

I think it really depends on the speeds you normally drive and what type of truck you have. At 75mpg, stick your hand out the window, there is significant drag force. It *can* make a large or little difference.

Frank.

Being that I've actually studied aerodynamics to some degree in college, I thought I'd chime in.

Dave - Although the decrease in drag from removing the tailgate may be part of the reason, it's probably only a VERY small part. Most likely, his faster time has to do with the decrease in weight of the entire vehicle. Tailgates simply just aren't that light.

Mechanic58 - If you don't want to benefit from the possible benefits that lowering the tailgate can afford, simply don't do it. Some people, travel ALOT! And 30 miles per tank can add up so a decent amount of money over the course of a year. So, I wouldn't go making fun of people for doing it.

All - I've read a number articles surrounding this topic. Simply put, sometimes lowering the tailgate works, sometimes not. It all depends on how the engineers designed the truck. If it was built with drag in mind, usually leaving it the way it was intended (or putting a tonneau cover) is your best result. Now, to the Porche arguement... I had learned in school that your most aerodynamic shape is a tear drop with the fat section facing forward. Nature proves this point over and over. Take a drop of water and let it freefall. Look at the shape in mid-air. Nature always creates the perfect design. Now the reason the Porche has a small coefficient of drag is that is pretty closely resembles a teardrop. Think about it.

Oh well... enough of me. I hope this was informative to you all.

David <img src="/forums/images/graemlins/kewl.gif" alt="" /> <img src="/forums/images/graemlins/cheers.gif" alt="" />

You are right, vortex is the singular, vortices the plural. My fluids teacher didn't have the best command of the English language as with many of my instructors, it is his second language.

Frank.

I'm claiming BS on this one. The Vanagon, which was designed to be more aerodynamic than its predecesor has a drag coefficient of .44. The 'vette's I found are around .29-.3. So please produce the data AND test details because this one is a little hard to swallow. Are you sure you confused with a claim from VW that a "long" time ago it found the bus has a lower coefficient of drag than the beetle?

Also, the actual equation for drag force, which is what really matters because that is the force your motor is resisting, is.... force(drag) = (drag coef).5(density of medium)(velocity squared)(area) Please note the last number, the area. Even if the VW bus had a lower coefficient of drag, it has WAY more area and will have to fight a much stronger drag force.

Frank.

Before i added my Tonneau cover i got aobut 17.5 mpg on average, no after a soft top tonneau..(TekStyle, form summit Racing) i get a lil over 20 when i try to get good gas mileage, going form NV to california i've gone form 20mpg to 22 mpg, so it does make a differnece, tailgate down i think was a lil under half the gain i got form the tonneau

Pay attention...I said "STINGRAY" bodied corvettes. Pre 1968. The Bus in question was about a '62 model panel...no side windows and no camper top. Just a plain old smoothie.