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Twerp 06-30-2008 03:03 AM

Conservation and the Frozen Tundra
So this is the saga of my build project for my truck. It will prolly be pretty drawn out because I don't have a lot of free time and once my Civic gets out of the shop, I will start working on that instead.

So far, I've added a Scan Gauge and I've been working on my driving technique and so far, the results have been astounding. I used to average 18-20 mpg. Since I modded my driving along my work commute, I've increased that to 24, 25 and close to 26 mpg. The Scan Gauge is helping the current tank quite a bit. If my estimates are right, I should hit close to 28mpg. Not bad, but I want more. So here are the plans:

First, an aero cap! Then possibly some underside solutions and a partial grill block and maybe some kind of wheel skirts. Suggestions are welcome.

I've already got a lot of the materials for my aero cap, and I've started construction on the frame. If I can successfully attach a picture, I'll show you what I have so far...

The tabs sticking out of the back will eventually be trimmed off. With the base assembled, I want to start working on the top, but I'm torn between two possible designs. The predictable option is just to go in a straight line from the cab to the tailgate. What I want to do is go back at a flatter angle and then angle toward the tailgate from there. This has two major advantages. One, it allows more cargo room. Two, it angles the rear window a little so that better visibility can be attained without using too much transparent material. Here's what I'm talking about:

My apologies for the cheesy MS Paint edit and the poor perspective drawing...

The other design would look more like this:

And this just amuses me:

So my question is, which cap design should I go with? I like the multi angle design, but aerodynamics is really what it's all about. So what do you think? Any suggestions?

JJW 06-30-2008 09:44 AM

If it were mine, I'd be trying to emulate the following shape (excuse the rapidly made craptacular 'shop):

I hacked on the back half of a prius, rescaled to the same length as your roof peak to tail end. I grabbed the point where the rooflines both become level. I also put on a bloody great air dam, because its the ecomodder version of putting on a flame job in photoshop :thumbup:

It might be acceptable to simply slope from the rear of the roof to the tailgate top, though. It appears that's how Phil Knox did it, and I don't pretend to know nearly as much about aero:

But I wonder if there is a problem with maintaining attachment over the transition from roof to slant back. IF there is, some VGs might help just forward of the transition, or perhaps the more gentle slope of the curved prius-style kamback would be better.

Anyone with more aero knowledge care to do a mock up? Here is an excellent Tundra side shot:

ebacherville 06-30-2008 10:11 AM

the prius graft is about what you want.. a gradual curve, less angle at the cab and more near the tailgate.. up to 15 degrees. From cab to tail gate may be too steep raise the rear at the tail gate a bit to lessen the angle of the slope, also slope in the sides a bit so there more horizontal in back than near the cab.. this is what is more ideal.. however even a straight slope would help, but if your going to go through the efforts.. might as well do it best you can.

JJW 06-30-2008 10:55 AM

"Artist's" Concept #2:

garys_1k 06-30-2008 12:52 PM


Originally Posted by JJW (Post 39722)

Might want to terminate the arse end as more of a Kamm-back.

Twerp 07-07-2008 01:58 AM

Progress was made!
It wasn't much, but JJW and I worked the frame a little more. We're going for the curved look which he suggested earlier. We purchased some cheap supplies and after half a Saturday's work, we are most of the way done with the frame. I'm crediting him with most of the design and cutting as well as the photography. Hey, 2 out of 3 talents isn't bad.

So here are the bulkheads...

Here's another angle which includes me, between adding support screws

Here is a shot with two of the stringers installed. It's actually not as dark as it looks.

And another angle

Hopefully next weekend, I will be able to install the other four stringers. After that, I think upholstering it is going to be the next step... Then there will prolly be something involving fiberglass resin and then maybe some mold making and fiberglassing and surfacing and painting and so on... It's going to be a long project, but hopefully it will look decent when it's finally finished.

ebacherville 07-07-2008 02:26 AM

looking great!! my next project is for my 2005 colorado.. to make a area topper almost like what your doing. Ill probably also consider the same for my 8foot box on my 93 dually 1ton chevy diesel (after the veggie converson) Keep up the great work.

JJW 07-07-2008 01:12 PM

It's worth pointing out that those bulkheads are going to be trimmed to allow for rear visibility, but we left them solid for now until everything is more structural. The two stringers shown will have acrylic window material between them, hence the wide spacing. We were both fairly impressed with the quality of the shape we were able to produce using this method, I think it was better than either of us had anticipated. It looks like a small row boat off the truck.

Twerp 07-13-2008 11:15 PM

Well, we made more progress on the cover. I have photos, but they aren't uploaded yet and I'm at work, so give me some time on that one, k?

We finished building the frame and upholstered it with cloth. It has really taken shape now. It looks like the back end of a really aerodynamic race car. Hopefully, after I get paid this week, I'll be able to pick up some fiberglass resin and give it a good coating on Friday. At that point, I will have a functional unit, I think.

Now, we didn't put any windows in it. We prolly could have, but I got lazy. The plan is to mount it and test it. If I can get some confirmation of its functionality, I will consider making a mold of it and creating a copy out of straight fiberglass. I will be able to cut windows into that pretty easily. For now though, I'll be very happy to just put it onto my truck and go riding around with it.

Twerp 07-29-2008 05:47 AM

There was more progress on the cap since my last post... Unfortunately, not as much progress on getting pictures posted. They are currently being held for ransom on somebody else's camera.

We applied some fiberglass resin to the cloth upholstery in hopes of stiffening it. The upholstery is two sided. It is a lined burlap with one side being, you guessed it, burlap and the other being a canvas like material. Well, we had the canvas side up and the resin didn't really stiffen the canvas that much. We did discover that where it soaked into the burlap around the edges was really strong. So we flipped the thing over and applied the rest of the resin to the burlap. We didn't have enough resin left to cover all the burlap but the areas that we did get are all nice and rigid.

So the next step has been to wait for my fume filled lungs to recover and my damaged brain cells to grow back. So far the lungs are good, but I've been waiting on the brain cells for an awfully long time. After that, I'm going to coat the rest of the underside and hit a few spots on the surface for waterproofing purposes. Then it's sand and paint time. I'm considering acquiring a rear view camera system (saw it at Walmart for less than $100) instead of trying to apply windows to this thing.

Twerp 07-30-2008 02:55 AM

Hostages freed!!
Well, finally got my pictures. I didn't have to pay ransom or anything. It actually happened with a sneaky rescue mission involving a double agent, a well trained sniper, a talented but cocky helicopter pilot and some homemade cookies. No, this didn't actually happen, but I thought I would just put the suggestion in the thread for when it eventually gets made into "Conservation and the Frozen Tundra: THE MOVIE!":cool:

Anyway, here are the pictures which are cool, but not nearly as interesting as my nifty plot device...

So, here are some shots of the completed framework.

Mind you, I'm not the photographer for any of these...

The stringers on the sides were difficult. Where the other ones just had to bend a bit, the ones on the sides had to be twisted. We managed to do this while only accumulating a few splinters.

And then we upholstered the thing.

I don't have pictures of it since we coated it in resin, but just try to picture it looking goopier and kinda amber colored. I may take those pictures eventually, or I may just wait til it's sanded and painted. Not sure.

JJW 08-04-2008 09:36 PM

That's a thing of rural New Hampshire redneck beauty, right there. It "looks fast", doesn't it?

By the way, bonus points for the biodiesel drums in the shot.. and 1/4 extra points for getting my Yaris in there too.

Big Dave 08-05-2008 11:00 PM

Your bed cover look a lot like mine. You'll find they work well. Now to make mine more practical.

Twerp 08-05-2008 11:34 PM

I think mine will be pretty practical once I cut out a section of that center bulkhead. Then there will be a nice amount of usable space under the thing. I should be able to accommodate most types of cargo that I carry with the exception of my four wheeler. Plus, now my bed should be water resistant! :thumbup:

I've actually attached it to my truck and I got to drive with it on my way to work tonight. I got to make some seat-of-my-pants observations and initially, they look promising. I'll do all the nice sciency stuff when I have it 100% completed. For now, I've seen roughly about a 1mpg increase. There are a few caveats which make that more interesting though. First, it's not completed. There is a decent sized gap between the cap and the cab which is prolly destroying some of my air flow. On my way to work, I was, well, a little excited and as a result maybe a little heavier on the throttle than usual. I was also trying to maintain higher speeds to take more advantage of the aero improvements. If I had to guess at what my mileage would have been with the heavier throttle and no cap, the cap may have caused closer to a 2-3mpg increase.

It seemed like it coasted a little better at the 40-55 mph range, which is the fastest that my commute gets. During one of the EOC downhills, it approached speeds 2-3 miles faster than usual. Nothing is very precise about these observations and there is a ton of variables that could make them invalid, so I won't know anything for sure until I can do some hard, precise, number-based testing. For now though, it looks promising. And my personal educated guess is that once the gap is filled, I could see a 2-4 mpg increase on my commuting mileage. For any other trips which involve a lot of highway travel, my mpg increase might be more significant. That's what I'm hoping, anyway...

Big Dave 08-06-2008 06:00 PM

Yeah, you gotta deal with that gap. I found my cab slants away at a seven degree angle. Yours is probably about the same angle, plus or minus. As a result I had to take a seven degree cut off the bottom of the front bulkhead, so the gap at the top doesn’t get too big. You might consider removing your center brake light fixture to enable you to scooch the bed cover tighter to the cab. I also fishscaled the bed cover versus the cab by about an eighth of an inch to allow for seasonal variation in the wood structure. Even plywood swells a little.

One thing I noticed right away was the reduction in wind noise in the cab of my truck. Energy was not being converted into noise. I occasionally have to take my fairing off and am amazed at the roar from the bed area.

Twerp 08-06-2008 11:53 PM

My plan is actually to pour some of that liquid foam into the gap and then sculpt it flush from there. I plan on stretching some plastic over the back of my cab and then masking the gap between the bed and the cab. I will then put the cap on and mask the gap on the sides between it and the cab, creating a little bucket to pour the liquid foam into. If everything goes according to plan, it will adhere to the cap and I'll just have to smooth out the top a little and it will be pretty flush with the cab. I will then remove the cap and strip the plastic away. I will grind it down a little bit and put a skim coat of body filler on it and the rest of the cap. After a bit of sanding, it should be ready for paint.

I've discovered that Rustoleum's dark gray metallic is a perfect match for the color of my truck. A few coats of that along with a few coats of clear coat should make the thing look like a Toyota accessory.

Tourigjm 08-07-2008 07:56 AM

looks nice,cant wait to see the finished product!

Twerp 08-07-2008 11:26 PM

Neither can I. I've been roaming around with this thing on the back of my truck and it totally makes my truck look like a covered wagon. Once it's all painted, it will totally look like it belongs there.

JJW 08-12-2008 01:45 PM

Cab slant
I just wanted to point out that when we were making it I designed it with about a 5 to 10 degree forward slant at the front, and the rearmost bulkhead perpendicular to the plane of the bed. A bit of shortsightedness on my part resulted in the rear bulkhead leaning back, so now both ends "splay" out a few degrees each, and the front gap grows toward the top. The "stringers" are actually stressed members in the design and the whole thing "corrected" itself.

The other secret is that we tried a slightly different method of "glassing".. The secret being there is no glass involved. The substrate for the resin is some hefty hemp burlap backed sail cloth we found cheap at a local fabric supply shop. I bound two 54" pieces to make up the width and upholstered the cap like a piece of furniture.. Then Twerp and I applied the resin to both sides (He did about twice as much of that than I did). I haven't had a chance to see it since the second such application, but the first made it fairly stiff and certainly strong enough for the task. I was concerned about weight but the two of us can still move it fairly easily.

Twerp 08-13-2008 12:22 AM

After running around with it on in the rain, I noticed water marks beginning to form around the bottom edges of the cover. It looks like I'll have to do a little extra waterproofing to the cloth at the attachment points. Hopefully the weather will let up this weekend and I will be able to do that and get the front part of it foamed and sculpted.

edllorca 09-28-2008 12:31 AM


I just read your thread as I have built a sloped rear cover too. not to hijack this thread but can you briefly explain how you got from 18-20 al the way to 26 just by changing driving technique?


Twerp 09-30-2008 02:41 AM

The cap's progress has actually been stalled. I'm waiting to finish it, but I'm in the process of moving as well, so ecomod projects have been put on the back burner for now.

As for what I did to improve my mileage up to 26mpg, well it's a combination of things. Prolly the biggest contributer was the route I was taking to work. The max speed limit was 55 and the min was 30. I averaged about 35 according to my scangauge. There were only about 8 or 9 stop lights and I would hit most of them when they were green. I work the night shift so there was very little traffic on the way to work. It was also cooler so I could run without AC, windows closed and vent fan cranked during the summer. Since I have a stick, I could make up a lot of the energy spent going up hill by coasting EOC downhill and there were some long graceful downhills which would allow me to coast within a reasonable percentage of the speed limit.

For your purposes, here is my advise:

1. Get a Scangauge. If used properly, it will help you save enough gas to pay for itself and then some. Mine paid for itself within a month or so. Program it so that you can view your Average trip mpg as well as your instant mpg. This will help you notice when you burning more gas than necessary.

2. Prolly the most obvious, but so often overlooked. Don't go over 55mph. Let people pass you as needed and try to be patient with tail gaters.

3. Get friendly with mapquest. Engineer your route to work. You want to see if there's a rural route that you can take. Try to avoid highways or excessively fast roads as well as excessive traffic or stop lights/signs. At the same time though, try to figure out the most direct route. Remember that getting 26mpg out of a truck is great but not when you end up adding another 10 miles to your trip. The Scangauge will allow you to view how many gallons you've burned on a trip. Use that when comparing routes.

4. Get intimate with your vehicle. No, don't sleep with it, but turn off the radio and listen to the engine. Get a feel for what the engine sounds like at various speeds and various gears. Play around with the RPMs and gearing. See how low you can keep your RPMs without losing speed.

5. Get intimate with your route. Again, don't sleep with it, but once you've selected your route, practice it. Get to know every hill, speed limit and curve. Try to get a feel for the areas where you can lay off the gas and let the vehicle go. Figure out those areas where you should gradually increase your speed to prepare for ascending a hill. Keeping track of the your trip mileage on the Scangauge at certain points on the trip will help you compare your current mileage with previous trips to see if you are making improvements on that section of the road. For example, I know that when I hit the Goffstown center, I should be at 25 mpg for the trip. I can expect to be at around 26mpg by the RV dealer. I'll lose some mileage going up the hill, but if I crest it around 24 mpg, I can get it back up to 25 by EOCing down to the center of Weare. I have to hit my brakes once halfway down the hill so I don't go over the speed limit by too much, but I also don't want to slow down too much because I want to be able to coast all the way past the convenience store. You know, that type of thing...

6. Go through the driving tips mentioned on the home page of ecomodder. The basics are conserve momentum and minimize idling. Pump up your tires a little bit to get rid of some rolling resistance. Carefully practice the DNB concept. Obviously, use your brakes when you need to slow or stop, but try to plan your accelerations in a way that you don't have to use your brakes as much. Less accelerating equals less gas burned. Try to time lights so that they turn green before you come to a complete stop. Depending on traffic, you could try some pulse and glide. If you have a stick shift you could do some engine off coasting (EOC), especially for some of the longer downhills. Just be aware of your steering lock and the key position which engages it. This goes along with being intimate with your vehicle.

7. Make sure your vehicle is well maintained. You know, go through your manual and make sure that all the scheduled maintenances have been done. Make sure your oil is getting changed on time. Oh, and look into Seafoam. You can apply it to your gas and oil and it cleans everything up pretty nice. When I get bold, I'm going to suck some into the breather and really get the gunk out of my engine. Check out videos of Seafoam in action on youtube. Just make sure you're not Seafoaming your breather when your neighbors are having a get together because you will totally crap on their picnic.

8. As winter approaches, I may get an engine heater so that I can reduce the amount of time that my engine runs rich while it gets to operating temperature. During the summer, there really is no need to let an engine warm up before driving off. Winter is different. Having the engine pre-warmed will eliminate the need to sit there idling and wasting gas. I just need to see if I can run an extension cord to my truck while I'm at work. At home, it won't be an issue.

I hope that helps. Try some of that and see how it goes. Aside from the Scangauge, it's all pretty cheap. Oh, and if you do pick up a Scangauge, be sure to phone them up and mention that you are a member of We get a discount.

truckncycle 09-30-2008 12:00 PM

The cap looks great. I was thinking of using a similar technique. It reminds me of old airplane construction. I was a little worried that the cloth would sag as I was adding resin to it and I decided to fiberglass over rigid foam instead. I am probably half way done. Mine looks almost exactly like one of your original two options. It has windows in the sides and the back. I am looking forward to seeing yours completed.

edllorca 09-30-2008 10:36 PM

Thanks for the tips. I am new to hypermiling so the numbers posted are a little shocking. Having bought a scangauge I can start measuring my progress. my truck (2000 dakota 4 door 2wd w/3.9lv6) is an automatic but I have done some neutral coasting but not full eoc. I built a mockup bed fairing with the leading edge 10" higher than the bed edge. This is as high as I can go and still see out the back. I will add a fairing to the cab trailing edge and I figure I will get 90% of the gain and still have good rear visibility. I have not decided how to proceed beyond that on the aero front. The motor is going to need some work so I am outlining those steps in my head too.

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