having the tailgate down make when running 1/4 mile, or racing somebody from a roll up to 120 MPH?

A friend of mine whom had a pretty quick Lightning swears there is a world of difference. He seems to think 2-3 MPH in the 1/4 mile. I say not.

Anybody out there test or race somebody both ways?

 

hell who knows
I still run with my tailgate and wing on the back

 

I've done a LOT of searching for truck aerodynamics.

What I've found are conflicting reports. My thoughts are at the track it doesnt make a bit of difference. I ran with and without the tailgate up. Net me -0-. This was with an open bed.

I've never run my truck with a tonneau on - I always roll up my soft tonneau. When driving on the highway with the tonneau on, I notice 2 areas of different air pressures on the bed. One behind the driver's window is a low pressure area (the tonneau lifts), and at the last 1/3 of the bed, it's a high pressure area (the tonneau is being forced down).



On or off, tailgate up or down - From what I've seen it really doesn't make a difference. Test it for yourself at the track.

 

I forget where I read it but it was a magazine that did a wind tunnel test and they said it made very little difference but that keeping it up and closed was slightly less drag.

 

Just take it off. It takes all of like 30 seconds to remove it. Removing 30 lbs will definitely get you down the track quicker.

 

Without a tonneau, putting the 'gate down slightly increases drag. Doesn't seem like it would, but it does.

There are wind tunnel research reports available, and NO, I can't link you to them right now. If you do a cursory search, you will turn up several message board discussions, some of which will cite research that actually favors putting the 'gate down. I've seen an original paper and it indicates leaving the 'gate up.

All of the various quoted sources agree that removing the tailgate is the worst possible configuration (as far as aero drag goes), plus you will move the center of mass marginally forward.

We did the experiment with my bud's 4.6 NASCAR edition and it definitely ran faster with the tailgate up.

With the 'gate down, the drag is marginally higher, but you do move the center of mass SLIGHTLY rearward and downward. Perhaps there is some MINISCULE traction gain.

A tonneau improves the drag situation considerably (supported by the research), and moves the center of mass rearward (traction). Not sure how much of these gains you give back in the form of added mass - probably all of it.

 

I found some threads on this and strangely enough it seems the tailgate up is the best way to go, just as was mentioned here.

It sounds like even if there was a difference, it would be in the 1/100's, and not 1/10's as my friend originally suggested.

I am not going to remove the tailgate because I think the weight off the back end would hurt more than help.

 

umm ford does wind tunnel design witht he tail gate on the truck. The desgined the truck with 4 walls on the bed, not 3. So you are only creating a vacuum.

 

http://popularmechanics.com/automoti...s/index5.phtml

http://www.awtrucks.com/tailgateup.htm

Hopefully puts the whole "tailgate up or down" issue to bed..


**EDIT! FOUND A GREAT STUDY!!**

http://sitemaker.umich.edu/um.gm.truck
I guess those spoliers on the SRT-10 RAM really do something!

 

I just tried this a few weeks ago a the track.

13.1@106 13.0@106 - Up

13.0@106 13.1@106 - Down

It didn't make any noticable difference

2-3mph? LOL...

I would be curious about MPG though crusing on the highway at 80mph for 4-5 hours.

 

Only reason I can think of to leave it down would be to move more weight farther rearward and farther downward.

 

TTA89,

I did the same thing as you back in 2000. I alternated runs with it up and with it down 4 times. If I had to say one way had an edge it would be up but it's really too close to call.