Pickup tailgate up or down

[skyl4rk]

It would be nice to have an inflatable pickup bed filler that could be strapped into the bed and inflated when the bed is not needed. Maybe it could even hang over the end of the tailgate and create a boattail.

Air mattress material is pretty durable, if it could be made to handle UV radiation and last a few years, it might pay off.

[aerohead]

Originally Posted by pasadena_commut

I've seen tests of up, down, mesh, covers, and partial covers. However I have not seen anybody try louvers. Naively it would seem like better flow might be achieved by placing a series of horizontal louvers (perhaps just thin boards) where the tailgate used to be. If it's too turbulent side to side vertical lovers could also be added. With proper design it might straighten the flow out of the bed of the truck. Might.

Louvers would be like "gate off".

[whokilledthejams]

When I had my S10 (short bed, regular cab, 2wd), I found I did the best with the tonneau cover on. No tonneau with the tailgate up cost me a few mpg. I never drove enough with the tailgate down or off to ever really quantify the effect of that.

Odds are, unless you have a really odd truck (and the original poster does not), you can probably find a cheap used tonneau, or even make one.

On the other hand, if you do lot of city driving, no tailgate would probably be best, as those things are right heavy.

An aero cap would be best (...if retaining the truckiness of the truck is important), of course, as they approximate a Kammback.

[twentysixtwo]

There was a SAE paper from some years ago which very clearly said that for larger trucks, gate up was better than gate down, though tonneau cover was better than either.

For smaller trucks (ranger sized) Gate up and gate down were fairly close though gate up still slightly better, I thing the length of the bed had some interaction. Tonneau cover still best.

I'd really shy away from the nets. I don't have any hard data, but 2 semesters of fluid mechanics and a year working in automotive aerodynamics give me the gut feeling that it's going to be much worse than gate up or gate down. Louvers are likely to have a similar effect to a net, though with perhaps less turbulance (and therefore better FE tan a netting gate)


I'd love for someone to post some coastdown numbers.

p.s. Mythbusters is total crap in their methodology.

[metromizer]

Originally Posted by twentysixtwo

...For smaller trucks (ranger sized) Gate up and gate down were fairly close though gate up still slightly better....

That was my result... I sooooo wanted to beleive gate down would be MUCH better, but not so. I was pretty careful during the 'tests' and the fact I averaged things over thousands of miles helped, but the numbers don't lie, any real difference was buried in the noise.

Originally Posted by twentysixtwo

p.s. Mythbusters is total crap in their methodology.

Ha! I thought the same when it aired... I agreed with the conclusion, but not the psudo-science. Not one of their better shows.

[MechEngVT]

I'll chime in here with anecdotal evidence since what little data I have is not from ideal methodology nor immediately at hand.

In my experience the best option is a "streamlined" bed cap, next to that is a flat tonneau, and next to that is tailgate up. This is with a Quad Cab/Short Bed combination.

I have no data but experience from towing open utility trailers has given me the hypothesis that the tailgate condition is more important on longer beds than on short bed pickups. It is possible that with a regular cab/long bed truck tailgate down may be slightly better than tailgate up, but I still cannot see how either could be better than a tonneau or tapered cap.

When my truck was only a few months old I took a highway trip from MD to GA down I-95 most of the way with a combination of our "new couple" holiday gift haul and moving some last items out of our parents' homes. My truck bed was loaded cab-high at the rear window and tailgate-high at the gate, covered in a blue tarp and bed net. The load was bed-wide at the rear window but got narrower (still gate-high) toward the gate. Since the net made the tarp hug the load, this approximated the "ideal" aero bed cap. Without trying, heavily loaded, with the cruise set at 75mph in a truck that was not completely broken in I pulled high-19s mpg when my previous best highway trip was 17s. I haven't been able to replicate this bed condition.

About two years after this I bought a soft tonneau cover and saw an average increase of 1-1.5 mpg IIRC, comparing long-term averages before and after but not A-B-A.

Towing a 16' utility trailer with 3' high wooden sides and solid 3' high tailgate I could barely pull past 65mph and was seeing instant readouts of 10-12mpg on flat ground (unloaded), so I shouldn't have been towing that in 5th. I stopped and yanked the gate and strapped it to the front floor of the trailer and could easily pull 70 in 5th with flat-ground instant readouts of 14-15 mpg. I think the trailer was long enough for the bubble of circulating air to end and the flow to approximate laminar on the trailer floor. This may happen in an 8' truck bed but likely will not in a 6' truck bed.

[twentysixtwo]

Originally Posted by MechEngVT

I'll chime in here with anecdotal evidence since what little data I have is not from ideal methodology nor immediately at hand.

In my experience the best option is a "streamlined" bed cap, next to that is a flat tonneau, and next to that is tailgate up. This is with a Quad Cab/Short Bed combination.

IIRC this agrees 100% with the SAE paper I read. It was from about 1990. There is another one here from 2004 which is very similar:

http://ecow.engr.wisc.edu/cgi-bin/ge...hi1/pickup.pdf

BTW they only tested the mesh gate on one config but it performed very poorly. The Mythbusters are busted again.

[extragoode]

Originally Posted by MechEngVT

I'll chime in here with anecdotal evidence since what little data I have is not from ideal methodology nor immediately at hand.

In my experience the best option is a "streamlined" bed cap, next to that is a flat tonneau, and next to that is tailgate up. This is with a Quad Cab/Short Bed combination.

I have no data but experience from towing open utility trailers has given me the hypothesis that the tailgate condition is more important on longer beds than on short bed pickups. It is possible that with a regular cab/long bed truck tailgate down may be slightly better than tailgate up, but I still cannot see how either could be better than a tonneau or tapered cap.

When my truck was only a few months old I took a highway trip from MD to GA down I-95 most of the way with a combination of our "new couple" holiday gift haul and moving some last items out of our parents' homes. My truck bed was loaded cab-high at the rear window and tailgate-high at the gate, covered in a blue tarp and bed net. The load was bed-wide at the rear window but got narrower (still gate-high) toward the gate. Since the net made the tarp hug the load, this approximated the "ideal" aero bed cap. Without trying, heavily loaded, with the cruise set at 75mph in a truck that was not completely broken in I pulled high-19s mpg when my previous best highway trip was 17s. I haven't been able to replicate this bed condition.

About two years after this I bought a soft tonneau cover and saw an average increase of 1-1.5 mpg IIRC, comparing long-term averages before and after but not A-B-A.

Towing a 16' utility trailer with 3' high wooden sides and solid 3' high tailgate I could barely pull past 65mph and was seeing instant readouts of 10-12mpg on flat ground (unloaded), so I shouldn't have been towing that in 5th. I stopped and yanked the gate and strapped it to the front floor of the trailer and could easily pull 70 in 5th with flat-ground instant readouts of 14-15 mpg. I think the trailer was long enough for the bubble of circulating air to end and the flow to approximate laminar on the trailer floor. This may happen in an 8' truck bed but likely will not in a 6' truck bed.

I had a similar situation. About a dozen people were roadtripping from Iowa to Florida. Everybody else had cars, so we had 3 cars with 4-5 people each and everybody's stuff in my S10; at least 500lbs worth, but probably closer to 700. I got averaged 26mpg on that trip, better than some of the cars. My previous best was only 27 and that a similar situation. About 200-300lbs packed the bed to about half max capacity. My daily average in that truck was usually around 24 until a couple years later when a ring in the fourth cylinder started loosing compression. Then I would get 20-21.

[MetroMPG]

From Phil's gallery:

[extragoode]

What exactly is meant by basic redesign? Buy a car?