truck aeroback
 

I've got a new idea for Stinkerbutt. We've all seen Phil Knoxs' truck. I've got an idea that I'd really like to try. I don't know how many of you have seen a Dakota (2nd generation) in person but the rounded fenders and front end really lend themselves to aero mods; look at me, 26 mpg on the highway. Now I want to take it to the next level.

Picture this:

The truck currently has a soft cover. Take that off. Get one piece of Lexan the size of the rear window. Get another two in a triangular shape, the point of which will be at the tail gate.

Now mount the triangular pieces of the Lexan to the bed. Mount the piece the size of the rear window at the...rear window. Mount the bed cover to that. The front of the bed cover will be just below the top of the cab, the bed end will be where it is now, even with the top of the tailgate. What we're going to do is simply raise the front of the bed cover.

So the Lexan allows one to view over the shoulder out the bed for traffic and safety purposes, the current bed cover mounts to that. Now we have the "ice cream cone" shape for the back of the truck.

I'll shoot a short video of this concept tomorrow night.

To review: the current bed cover will be (at the front) about at the height of the cab. It will end at the tailgate where it is now. The sides and front of it will be Lexan which will allow seeing traffic while driving. What I'm proposing is just raising the front of the bed cover to the the level of the cab; instant ice cream cone shape.

Now, because the cab curves in at the top on this model, I'll have to add some canards to direct the air flow past the new top as it rises to the top of the cab. Again this will be in my video presentation.

How will you see out the back? If you are installing a large piece of Lexan already, just leave the bedcover in place and set this on top. The bedcover won't stretch from the top of the cab to the back of the bed anyway, if I understand what you want to do, the bedcover will be about a foot short.

It will be 3" short ;)

Mine was very easy to make. Too bad my fiberglass didn't cure lastnight, it'd be on the truck right now.

It's not truly a cone shape - more of a wedge.

Ideally, you would round the "shoulders" of the aeroshell to soften the transition from "top" to "sides".

That said, we have to compromise sometimes, and your plan is surely an aero improvement over just the stock tonneau cover.

That's the purpose of the Lexan; so I can see into the blind spots. Rear views are not required on a commercial vehicles in Michigan.

My calculations show that the existing cover would be about 1.95 inches short of meeting the edge of the tailgate; a deficit easily made up with aluminum stock.

I say go for it. Looks like a decent plan.

Well, yeah. But we don't know if it will actually make any improvement. I mean what if the shape of the front of the Dakota (admittedly pretty darn smooth lines for a truck) negates the need for a cover like this. Yeah, I know Knox had great results and data says that this is the best shape but this ain't a square front design. But the math of adding a spoiler to the roof of the thing said that the air should spill over the tailgate and it didn't. I knew the air dam and side skirts would make a difference - it'll help with on any vehicle. But once you get to the top, well all bets are off.

And lets not forget; The 2000 was the first year that they left off the wheel well flairs. Not from a styling standpoint but because a Dakota gets better mileage with the tires sticking into the air stream. The mileage went up 1 mpg without them, via the EPA.

As an aside, did you guys notice that the EPA has updated all the mileage estimates for years past to the '08 mileage? Mine went from 14 city/20 highway to 13 city/18 highway. Which makes my garage entries look that much better. :) :) :) :) :)

Well, even though it was a windy day, I got 22 going to Detroit and 20 coming back.
That was with my aero cap, cam advanced 4 degrees and Halo plugs.
My Dak is a 98 with those fender flares, flairs... whatever. Should I take them off???

Nice mileage kitcar! I'd like to see some pics of your aero mods. When did you add the cab spoilers? Did it make a difference in FE? I didn't see that your gaslog.
Pics please:) . I want to do something for my gmc soon. Describe a little bit of your construction steps and materials.



thanks

what engine do you dakoda guys have?!?! cuz my s-10 with a 2.2L 5speed gets 25 26mpg and i have done zero aero mods. all ive done is cheap intake and electric fan... open bed too.

i plan to get a toneau and ive heard checkmate is one of the best. for a hard top (i want hard for security reasons) but thier still like $400 and take 5 weeks to build and ship. im thinking i could build one cheaper than that. get some aluminum bar stock build a crude frame and then get a HUGE piece of either somewhat thin aluminun or steel or somehting....get some hinges and a gas strut to hold it up and a lock mechanism and im sure i could build one for less than $400

I used 11/32" plywood, 1X4" and 1X2" wood to build. Only needed two sheets of plywood. The top one was only cut to length. The sides slanted from the outside edge of the box to 8" inside to meet the top as it turned down. The shape turned out awesome! Too bad I wasn't a body man. I got pics at home I'll have to update my Garage here.
I am currently cleaning out the garage to move the hovercraft out and the truck in. Even though I just did some engine work and a new tranny, now the rear end is toast. So once it goes in, the fuel system gets modded.

Oh yea, it only took me a weekend to build, more time to glass and paint.

I actually am kicking around using flooring underlayment for the body of it, design it so it will lock and open and coating it with fiberglass fabric. That way I'll get that bumpy paint I've been after. :) :) :cool: :cool:

Oh yeah. Almost forgot (not!). Filled up tonight and drove the 10 miles home.

28.5 mpg in rural/city driving (5 stoplights, 4 stop signs) using hyper shifting and driving. That's my personal best. Ye-haw! :D :D

Ok, Here are the pics of my AeroCap so far. $52 worth of materials.
I plan on modifying it later for easier access to the box.

that looks really good. i like the smooth flow of the back.
just a thought, have you looked into air bags for the ride height? from what i have read they work well.

I like that. Some kind of access hatch and some gas struts under there and you will be set.

That is pretty much what I have envisioned. It looks great :) . My 8 ft box will require a longer sheet or I'll end up with a seam for the pieces. That's what caulk is for :D .

Now that right there is what the heck I'm talking about. Put some fiberglas sheeting on it so it looks like one of them there hard tops and you're good to go.

Now we need some mileage stats. My Dak is a regular cab; 4.7 L H.O.(semi Hemi), 5 speed, 3.55 posi rear, towing package, 6 lug wheels, full option package and still 60 some % mpg over stock. And this thing will do mid 14s down the track, which leads to my HP/theory; HP/Torque = mileage. More HP/torque, less pedal, less gas, more mileage. I've proven it again and again. My last truck did mid 13s in the 1/4 and got 70% over stock mpg.

What we need to figure out is how much the mileage went up even with the extra weight of the cover over the weight of a vinyl cover. I'd expect that the additional mileage is way over the penalty . Then figure the payoff from the cost. With my sideskirts, front air dam and canards, I made the cost up with 2 tanks of gas.

Yea, I want to make easy access into the box but I have to build the frame for the hatch first so it doesn't lose it's shape when I cut it out.

Well for the longest time I couldn't break or even see over 18 mpg on the hwy. I got 22 in that bloody wind but only 20 on the way back.

Mine Dak has a Sport package, 3.55 posi and a 5.2 auto and is loaded with options. It had 65,000 on it when I got it. Now it has 164,000, tight engine, new tranny and soon to be rebuilt rear end.

Hey Max, maybe we should meet up in Lansing for a beer, then put my cap on your truck then do an mpg check. If it gets over 30, you're buying the beer!
I'll have to differential rebuilt first. It's in the garage now.

My box is 81" long and the top sheet is 84" long.
You gimme dimensions, I can draw it up fer ye. Inside and outside da box.

Thanks. I think the ride height is a bit high. I like it when I see these rice-burning-idiots taking the suspension out of their vehicles and grounding them out. Even my Soobie has 7.3" ground clearance!:eek:

These are the other pics of the cap. The front view allows you to see the taper back.

Since the truck is in the garage and I'll be waiting for the differential to come back, I'll be tweaking other mods. Also be taking measurements to build an air dam :D

wow that looks awsome. what #'s is that getting you? you have no gasslog and i want to check what your geting!!

Well, no gaslog yet because now I'm doing the rear end. Pinion bearings out.

As far as I can tell, being a windy day, it has netted me 4mpg but that is with Halo plugs and advancing the cam 4 degrees. That windy day shouldn't even be considered a mpg run. I'll do a better one but since the truck is in the garage, it's getting more mods >:)

BMac -

Just saw this in your garage. Stunning. Good aero and looks cool too!

CarloSW2

soft tonneau cover lift
 

Your thoughts. I have an 03 ranger edge with an extended cab,so this thing sits as high as a 4x4. It has the fendered rear box that is inset from the cab. I have a soft tonneau on it. I like the idea in the start of the thread about lifting the front of the tonneau, but understand the viability issue. So I went out to the truck, adjusted the rear mirror, sat low in the seat and marked the point on the rear window where the line of sight was at the top of the tailgate. Based on this measurement, I could raise the front of the tonneau almost half way up the height of the rear window and not lose any visibility. My question would be, does anyone thing there is any benefit in this, or am I wasting my time unless I go for complete smooth flow from the top of the cab to the rear of the bed. The current rear window height is around 20 inches with this vertical surface and I could lower that to about 10.

On a related topic, I am assuming that the rear tailgate area is a big deadzone behind the truck at speed. Would adding some type of diffuser at the top of the tailgate to create some turbulence be of any benefit?

Thanks

It sounds like it's worth trying.

Yes, it is worth trying, but remember that the airflow will not stay attached beyond an 11 degree angle.

i have a 2002 2wd 4 cylinder 5 speed toyota tacoma that i am getting around 30 mpg highway that i am thinking of doing this mod to. i am thinking about doing it with the tailgate removed so it will make more of a point at the back of the truck and less turbulance. the sides of the bed would just stick up above the wood creating like a rudder type thing.


i was thinking about making it so that it could be disasembled with a few bolt or screws and layed flat in the bed so i could carry stuff in the truck when needed


anyone have any thoughts on that. any real results on the mpg yet? i dont want to waste a bunch of time if it really dont have any effect.

i am collecting the material to make an areocap for my truck. i am going to make it out of wood because that is what i am most farmiliar with and i have wood around from the trade i am in.

i have been looking around on this forum and i see that there are a couple of people who have made them in the past. i have a couple of questions for you guys. i see that the guy who made the real nice fiberglass one for a ford f150 is claiming to get 4 mpg more. one thing i was told was to keep the angle around 12 degrees that would be a 9" drop from the cab to the tailgate. my cab is about 20" above the top of the bed so at the tailgate my areo cap would be 11" tall. i noticed on the cap on the ford f150 it seems to be about 5" tall at the rear of the truck. i know the ford has a 8' bed that would give it a little more drop but also i would think that the fords cab is taller than my tacoma. so i would think that aditional cab height would make up for the 8' bed. so i am thinking that the ford cap is more than a 12 degree angle. also i saw phil knox's truck with a areo cap and on his truck the cap goes to the top of the tailgate with no vertical section at the tailgate. so my question is how tall should i make the cap at the tailgate?

also i saw a plex glass areo cap that had a wing that extended a few inches past the the tailgate. also the fiberglass cap on the f150 had a small wing on the back of the cap that extended off the back of the cap. my question is when i am making my wood cap should i extend the plywood on the top of the cap past the tailgate and if so how far past the tailgate

I thought the best angle was 11 degrees, not 12. I would calculate (or just measure on the truck) it by that and allow the rear height be whatever it needs to be.

I don't remember the wing thing, but if it's like the lip that is common at the top of hatches on wagons and hatchbacks (like my 2008 VW Rabbit) then it's probably a good idea.

just as a reference:

https://www.evworld.com/images/pknox_toyota.jpg

I think a lot of times, people just wedge it down and don't pay that much attention to the angle. I have also heard a range of angles ranging from 9 degrees to 11 degrees (and new to my knowledge, your 12 degrees).

I think that the lip at the tail is more for air separation so that the air doesn't swirl as much when it gets to the end of your vehicle.

all that being said, I am not an expert in aerodynamics and am going off of what others have said.

one user on here (basjoos) has done a lot of aero work to his vehicle. I think he used 10 degrees for his rear. I talked to him once about it and he told me he modeled it after the rear of a certain airplane (can't remember which plain either)

https://i45.tinypic.com/jkei5c.jpg

putting a protractor on the back angle of basjoos's car the angle in the photo is about a 22 degree angle and the f150 areo cap is about a 14 degree angle. just wondering what made them come up with these angles?