Mythbusters did the tailgate thing and proved it lost about 1 mpg.
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| Truck bed covers and mileage https://slantsix.org/forum/viewtopic.php?t=29270 |
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| Author: | tlrol [ Sun Jun 01, 2008 8:04 pm ] |
| Post subject: | Truck bed covers and mileage |
I just finished driving across SD, WY, MT, and WA in my Slanted A-833 O/D 3.56 rear ended Super Six Weberized D 150--I know it is asking a bunch but I wonder if a Tonneau cover is good for a mile or two per gallon. I average about 15 mpg on this trip, with an average speed of 69 mph (per my GPS). Basically I sprinted from gas station to gas station, the speed limit is mostly 70 to 75 mph out west. Anyway, 15 mpg sems pretty good for these high speeds, but I recall watching Myth Busters a while ago were they found a Tonneau cover was good for a surprisingly notable increase in mileage, as well as a bump up in top speed. Any experience out there? |
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| Author: | coconuteater64 [ Sun Jun 01, 2008 8:41 pm ] |
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I have a camper top, and aluminum one. Your mileage seems exactly like mine at those speeds; if I go 60 mph I get a couple more. But it's aggravating driving that slow! I am wondering the same thing, since I want to get rid of my camper top to shed the old geezer look |
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| Author: | 68barracuda [ Sun Jun 01, 2008 10:16 pm ] |
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Yes it will work How much on your truck I do not know Over Here In RSA I have a 1/2 ton Truck(y?) With the tailgate in the horizintal ie open position I gain about 2,5 liters per 100 km - with a cover the same thing |
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| Author: | Reed [ Sun Jun 01, 2008 10:36 pm ] |
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I have been looking into vehicle aerodynamics a bunch lately since I am planning on building a fiberglass bodied electric car in the future. Truck bed covers do help the aerodynamics of a truck, a canopy is even better. But my research indicates that even better than a canopy or a bed cover would be a cross between the two. The best shape would be a bed cover that started at the height of the back of the cab and slanted down to the height of the lip. Make it solid out of fiberglass and it would help increase aerodunamics and reduce rear drag. Wheel covers and fender skirts also help a bunch. THen fabricate a belly pan for as smooth an underside as possible. Air dams help too. |
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| Author: | LUCKY13 [ Mon Jun 02, 2008 2:21 am ] |
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Yes it should help, and the more rigid it is the better it could work. The idea of coming from the top of the back side of the cab and going to the tail gate is a good one, but it would look a bit odd. The quick fix is the tail gate down trick, and it can give improvements. Everything adds up to help the big picture, and it seems to me that your messing some MPG even without these tricks. DO you have a A/F gauge to help tune that Weber in on your truck. One problem I see alot is when going that fast most carbs are trying to get into the power circuit and what happens is you can get better fuel mileage at a lower speed because its running at a leaner part of the carbs fuel curve. With a Weber it can get a little more tricky becuase of there unique tuning characteristics, but it can be fixed. I expect you may have about three more MPG (atleast) just from tuning the carbs fuel curve and maybe even the timing curve. BTW, the air bleeds in the Weber really effect when the main circuit start flowing. Jess |
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| Author: | Dart270 [ Mon Jun 02, 2008 5:44 am ] |
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From sources I trust, I've heard you actually lose mileage by leaving the tailgate down. This would take substantial controlled testing to see what the gains are for different arrangements. My bet would be that a camper top would be best, followed by a cover, followed by tailgate up. Reed's idea may work, but that slanted surface may create turbulent eddies worse than a flat rear panel. Look at the back end of a new Corvette... Lou |
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| Author: | Reed [ Mon Jun 02, 2008 8:08 am ] |
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If you are going to go through the trouble of fabricating your own bed cover and choose to try my "slanted" (heh) design, you may want to try adding somehomemade "air tabs" to the bottom of the canopy by the gate. See: this link |
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| Author: | slantzilla [ Mon Jun 02, 2008 8:57 am ] |
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Mythbusters did the tailgate thing and proved it lost about 1 mpg.
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| Author: | MoparBrit [ Mon Jun 02, 2008 9:58 am ] |
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I saw that. Found it very interesting. If I remember right they found that the tailgate up created an air pocket that ended up flowing the air over the back of the closed tailgate and actually improved mileage. At least on the truck they tested. With it down they lost mpg. They also did a test with a car on the with air condition on and with it off and windows down. Test was if the potential drag caused by the windows being down would actually cost mpg. Wish I could remember what they found. Anyone remember there? Think they still found that with the AC off they got better mpg, but don't remember on that one. Bit more on topic..... Back in the 80's I was heavily into trucks. We always put a cover on. Not sure if it helped on mpg, but sure was nice to have a place to store stuff out of site either way. We just built ours out of marine grade ply, covered it and put hinges in so the rear would lift etc. Pretty cheap and easy to do and was a lot less expensive than the hard plastic covers of the time. At an uneducated guess I'd say you might pick up a slight improvement in mpg, but I don't think it would be a huge amount going off mbusters. Guess anything helps though!!!!! Cheers |
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| Author: | Fratzog [ Mon Jun 02, 2008 10:13 am ] |
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I'd agree with Dart270 about the slant back possibly causing increased drag. This is one example of where aerodynamics seems to go against reason & logic, when a 'fast-back' can be in fact just the opposite. Its generally better to have a sharp cut off at the back of a roof rather than a long sweeping one. If you want to know the best way to make a truck cut the wind, take a look at what NASCAR does to their race trucks |
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| Author: | Reed [ Mon Jun 02, 2008 10:41 am ] |
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 That picture accompanied this article which you might be interested in reading. It discusses how a guy got 32 MPG out of a 94 Toyota 1/2 ton pickup using only aerodynamic modifications. I'll bet you could get into the 20s with a good tuneup and the right aero mods. Here is another place to look for fuel saving ideas. |
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| Author: | Dart270 [ Mon Jun 02, 2008 11:28 am ] |
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Interesting. I've been meaning to try some aero mods on my 68 Dart. It gets about 25 mpg now, but I feel aero is really holding it back now. Sandy's station wagon roof wing, a front airdam, and a belly pan seem like the places to start. Lou |
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| Author: | Reed [ Mon Jun 02, 2008 11:31 am ] |
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I am very interested in trying out a belly pan, rear fender skirts, and homemade airtabs on my vans. Supposedly a van is more aerodynamic that a pickup, but I don't know about that. |
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| Author: | bmimken [ Mon Jun 02, 2008 12:14 pm ] |
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I have a tonneau cover on my truck and I gained 1.5-2.0 mpg at highway speeds. It is a 99 Ram 2500 diesel, ext. cab, shortbed, 2WD, Automatic, with a Suregrip 3.55 rearend. Everything is stock on the truck. With diesel prices soaring, I figure the $200 investment in the cover eventually pays me back. Brian |
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