tailgate up or down? (mythbusters)

ozzyjim · 05-06-2006, 09:11 PM

Hi all,
not sure if this should be here but here goes anyway. I just watched on mythbusters an episode about driving with the tailgate up causes more drag than with it down. They both drive some sort of pickups which were identical with the same amount of fuel etc..

The results were suprising to say the least, the pick up with the tailgate down ran out of fuel before the tailgate up pickup did which ran a further 30 miles before running out. Then they use some form of wind tunnel (water actually), and found that the pickup model with the tailgate down caused more drag then the pickup with it up.

The pickup with the tailgate up caused a bubble of water in the bed and this in turn caused the faster moving water to glide over the bubble and pickup, where the tailgate down bursted this bubble causing the water to push down on the tailgate and cause more drag.

So basicly, what do you ute drag racer think? i know a lot of you put it down, have you guys tested this? I just this was an interesting show and would like to see your thoughts on it

Cheers
Jim

**Polyal** · 05-06-2006, 09:24 PM

phew glad I did a search.

I just caught the end of it.very interesting indeed as most drag people seem to think that it makes a difference having it down...anyone have any TIMED runs up and down?

The only thing stopping their theory with drag racing is the speeds. I dont think they measured how fast the flow was in the tank? There might be a critical speed where it actually makes a difference in a drag race.

ie - for the first half its not going that quick, but towards the end it might make a differnce.

sfr rob · 05-06-2006, 11:16 PM

Thats exactly what i thought would hapen if the tail gatewas left in, i gess what drag racers would do it for woul be to save some weight, not really aerodynamics.

Very interesting stuff though.

CAMS290 · 05-06-2006, 11:49 PM

Quote:

Originally Posted by ozzyjim

Hi all,
not sure if this should be here but here goes anyway. I just watched on mythbusters an episode about driving with the tailgate up causes more drag than with it down. They both drive some sort of pickups which were identical with the same amount of fuel etc..

The results were suprising to say the least, the pick up with the tailgate down ran out of fuel before the tailgate up pickup did which ran a further 30 miles before running out. Then they use some form of wind tunnel (water actually), and found that the pickup model with the tailgate down caused more drag then the pickup with it up.

The pickup with the tailgate up caused a bubble of water in the bed and this in turn caused the faster moving water to glide over the bubble and pickup, where the tailgate down bursted this bubble causing the water to push down on the tailgate and cause more drag.

So basicly, what do you ute drag racer think? i know a lot of you put it down, have you guys tested this? I just this was an interesting show and would like to see your thoughts on it

Cheers
Jim

I have tried it and i rekon it makes about 5/100ths difference, it definatly stops a kind of "vortex" happening when it is down.
Taking it off is the best option, both for weight saving and aerodynamics

**Polyal** · 06-06-2006, 01:04 AM

Cam, I dont know if I am reading your post wrong but they say flow is better when its up, with the vortex.

SpoolMan · 06-06-2006, 03:34 AM

I always raced with mine down, Hamo now does the same... interesting discussion.
What type of Utes were they?

CAMS290 · 06-06-2006, 01:12 PM

Quote:

Originally Posted by Polyal

Cam, I dont know if I am reading your post wrong but they say flow is better when its up, with the vortex.

I have found slightly better results with it down !!!
But .05 seconds could also be any variable, maybe my imagination too.lol

turboute · 06-06-2006, 01:30 PM

It also will move 50?kg of weight 20-30cm's back wich could give a bit more weight leverage for traction over the back wheels (maybe could help)

Judging by the amount of depression in my tonneu cover when I travel at 100km/hr I would guess that over 100km/hr it would be good keeping it down - I can actually feel the downforce this generates on the end of my ute - probably the evivalent to over 50kgs in the back of the tray at least.

ozzyjim · 06-06-2006, 01:46 PM

Quote:

Originally Posted by SpoolMan

I always raced with mine down, Hamo now does the same... interesting discussion.
What type of Utes were they?

All i know is that were big pickups US style.

Cheers
Jim

**Polyal** · 06-06-2006, 02:41 PM

which generally have the same tray style as our utes.

perhaps with drag racing it makes bugger all difference, but general highway cruising I think it woudl improve economy having it up.

dazzle260 · 06-06-2006, 04:14 PM

in my ute (which i had to sell for an extending family) there was a huge depression in the torneau cover right at the back suggesting the tailgate(and or tub) was stopping air from exeting cleanly. im assuming it would depend on speeds and exactly the shape of the ute also.

Quadcams · 06-06-2006, 07:02 PM

Quote:

Originally Posted by turboute

It also will move 50?kg of weight 20-30cm's back wich could give a bit more weight leverage for traction over the back wheels (maybe could help)

Tailgate weighs 25kg and power to weight is what you want, sticky tyres will fix the traction problems.

With tailgate up the air flows over the roof down onto the tray hitting the tailgate spiraling back creating a eddy of air which is creating drag, dropping the tailgate the air goes over the roof down through the tray and out the back no drag.

Myself always run with tailgate down even better off.

LUXO_8 · 06-06-2006, 07:05 PM

they were new F150's....

was very interesting i'll say....

ratter · 06-06-2006, 07:18 PM

If you run with the tailgate down it should be less resistance, but added bonus is..............

the paint chips you get in the tailgate will result in less weight, any one know how much a paint chip would weigh????

Lukeyson · 06-06-2006, 08:17 PM

but more drag if its down

rapidxr6 · 06-06-2006, 08:50 PM

The test on myth busters concluded that with the tail gate up the 'vortex' of slow moving air was created in the rear allowing the faster moving air to glide over it aerodynamically. With the tail gate down there was no or little vortex however the faster moving air puhed right down on the rear of vehicle, as a result excess force was generated to the rear axles making the car not as "efficient" due to this.
The purpose of the test was to find out which was more efficent, up or down in an open road environment.
However ...Drag racing ...well the extra down force on the rear axle with the tail gate down=quicker times to me.
So each purpose to its own gain.

:

_2:

Bossxr8 · 06-06-2006, 10:02 PM

Quote:

Originally Posted by rapidxr6

The test on myth busters concluded that with the tail gate up the 'vortex' of slow moving air was created in the rear allowing the faster moving air to glide over it aerodynamically. With the tail gate down there was no or little vortex however the faster moving air puhed right down on the rear of vehicle, as a result excess force was generated to the rear axles making the car not as "efficient" due to this.
The purpose of the test was to find out which was more efficent, up or down in an open road environment.
However ...Drag racing ...well the extra down force on the rear axle with the tail gate down=quicker times to me.
So each purpose to its own gain.

:

_2:

Makes sense that it creates downward pressure on the laid down tailgate, as it is similar to what doorslammers use with those big flat sheetmetal wings on the back for downforce on the rear tyres for extra traction. More downforce usually means more drag.

TruBlu351 · 06-06-2006, 10:17 PM

Their trucks were also dual cabs with only a short rear tray. It would have been better to see how a traditional long tray would go as the aerodynamics would be slightly different.

Would be intersting too see separate results with torneau or hard cover.

I think they ended up driving 600 miles (almost 1000km) to run the fuel tanks dry and then there was only about 30-40 miles difference. So on a quick 1/4 mile squirt, I reckon there wouldn't be much in it.

ozzyjim · 07-06-2006, 12:01 AM

So maybe it comes down to this, keep the tailgate up for less drag VS keeping it down for better traction.

Im guessing you ute owners would opt for the traction??

Cheers
Jim
ps. would like to see some back to back timed runs.

rodderz · 07-06-2006, 12:07 AM

I used to race mine with the tarp on, never tried the tailgate trick as everyone was getting stones flicked up on the return road from sticky tyres

**Charliewool** · 07-06-2006, 01:37 PM

What if you had a "variable" tailgate (ala Porsche Whaletail) that changed angle according to speed? (just watch your fingies when it closes automatically)

PhantomXR8 · 08-06-2006, 08:31 PM

Quote:

Originally Posted by Lowride260

Tailgate weighs 25kg and power to weight is what you want, sticky tyres will fix the traction problems.

With tailgate up the air flows over the roof down onto the tray hitting the tailgate spiraling back creating a eddy of air which is creating drag, dropping the tailgate the air goes over the roof down through the tray and out the back no drag.

Myself always run with tailgate down even better off.

Agree with Wade here, remove it!

Aaron_EF8 · 10-06-2006, 01:09 PM

Why not keep the hardcover fitted?

xr8ute · 10-06-2006, 01:27 PM

Quote:

Originally Posted by Aaron_EF8

Why not keep the hardcover fitted?

becuase they are real heavy

ReVd_uP · 10-06-2006, 01:35 PM

has anyone ever compared the difference running with and without the hard cover??

Quadcams · 10-06-2006, 02:40 PM

Quote:

Originally Posted by ReVd_uP

has anyone ever compared the difference running with and without the hard cover??

Go by the weight of a hard cover (40-60kg) you would expect atleast 1-1.5 tenths improvement without it, power to weight is everthing.

ReVd_uP · 10-06-2006, 06:50 PM

i think if i ever get to running my ute down the strip id leave it on, just so i get an idication of what id run in full street trim, probably leave the motorbike ramp kit and tie down kit bolted inside the tub too,... mainly coz id be too lazy to pull them out,...

MIEF9640 · 10-06-2006, 08:41 PM

congratulations lowride is exactly for that reason is reccomended that the tailgate be dropped nothing to do with traction if stone chips are a problem slow down on the return has been like that for 20 years and will never change if that is a problem lift the gate before returning oxford scholar not required for that idea power to weight is great idea for super stock but these are all street cars prostreet is illegal here unfortunately also on going through scrutineering it should be told to you that the tailgate is normally down during the run it's the same principal as windows are to be up also these issues are all to do with RULES OF RACING if that is understood....also if that bike rack is not secured to the floor you would be pulling it out before you got anywhere near the track let alone run down it ....

: :eclipsee_

ReVd_uP · 11-06-2006, 11:18 PM

dunno if you've ever seen the factory motorbike ramp kit, but the mount point for the bikes front wheels stays bolted to the front of the tub, the actual ramp stays in my garage....

outback_ute · 12-06-2006, 11:35 AM

I saw most of the segment, typical mythbusters really. As Trublu351 mentioned above they were big F150 crew cab utes which would minimise any tailgate effect (high cab and short bed compared to our utes). I remember seeing a concept truck years ago that was a hybrid or similar, it had a hard cover on the rear half of the bed for aero reasons which would contradict the mythbusters findings.